Ruba Hanna Majeed PDF

SEISMIC BEHAVIOR OF A SOIL-PILE SYSTEM
A Thesis
Submitted to the College of Engineering of
Al-Nahrain University in a Partial Fulfillment
of the Requirements for the Degree of Master of Science
in
Civil Engineering
by
Ruba Hanna Majeed Sa'ur

(B.Sc., 1997)
Sha'aban 1437
May 2016
ABSTRACT
Iraq is located near the northern tip of the Arabian plate, which is advancing
northwards relative to the Eurasian plate, and is predictably, a tectonically active
country. Seismic activity in Iraq increased significantly during the last decade. So
structural and geotechnical engineers have been giving increasing attention to the
design of structures for earthquake resistance.
Piles are one of the most commonly used foundations in seismic areas where the
soil is inadequate to carry the load on its own. In these seismic areas, piles often pass
through (penetrate) shallow loose and/or soft soil deposits and rests on competent end
bearing soils. Thus studying soil- pile interaction in Iraq under real earthquake records
is very important. In this study 3-D seismic behavior of piles in seismic active zones in
Iraq is investigated using the finite element program PLAXIS 3D 2013.
Dynamic properties play a vital role in the design of piles subjected to seismic
load. One of the main objectives of this study is to prepare a data base for the dynamic
properties of different soils in seismic active zones in Iraq using the results of cross
hole and down hole tests. The dynamic parameters of soil are used as input dynamic
data for PLAXIS 3D 2013 program, in addition to the static properties of soil collected
from soil investigation works.
From the data base collected it has been observed that the compressional wave
velocity is ranged from (1125-2500) m/s in the North, (306-1544) m/s in the Middle,
(805-1812) m/s in the Western south , (377-1326) m/s in the Eastern south and (334-
1404) m/s in the South of Iraq. And the shear wave velocity is ranged from (225-476)
m/s in the North, (111-408) m/s in the Middle, (268-659) m/s in the Western south,
(131-380)m/s in the Eastern south and (102-365) m/s in the South of Iraq.
Furthermore, Iraq sites soils are classified according to PISC (2013) and FEMA (2010)
as types (E,D and C) while according to Eurocode 8 (2004) as types (D, C and B).
I
The research showed the susceptibility of PLAXIS 3D 2013 program in
analyzing piles with different soil conditions under earthquake action.
The maximum bending moment during earthquake occurs at the interface of
different soil layers for each soil profile along the pile depth. Furthermore, the greatest
and lowest horizontal displacements occurred at pile tip and ground surface
respectively. And it is found that the shear and compression wave velocities play an
important role in estimating the dynamic behavior of piles.
Results of parametric study show that when pile length (Lp) increased, the
horizontal displacement with the deflected curve is increased due to increasing Lp/Dp
ratio where Dp is the pile diameter. And for Lp/Dp ratio higher than 10 the vertical
displacement of pile head increased with higher rate being enlarged by about ten times
when duplicate the length of pile. Also, there is increasing in bending moment value
and reducing the curvature of the pile deflected shape with increasing the pile
diameter. Knowing that, the maximum bending moment for 0.6m diameter pile is
about 90% lower than that for 2m diameter, while, the vertical displacement of pile
head can be decreased by about 70% with increasing pile diameter from 0.6m to 2m
for the same earthquake parameters.
Finally, it has been observed that the maximum bending moment increased by
about 20% with increasing modulus of elasticity of pile material by about 40%. And,
the results indicated that for Middle Iraqi zone the soil-pile system cannot sustain
earthquake of magnitude (ML) equal or greater than about 6.6.
II
CONTENTS
Contents Page
Abstract I
Contents III
Notations and Symboles VIII
List of Tables XI
List of Figures XII
List of Plates XVI
Chapter One: Introduction
1.1 General 1
1.2 Problem Statement 2
1.3 Scope of the Study 4
1.4 Thesis Layout 4
Capter Two: Literature Review

2.1 Introduction 6
2.2 Earthquake 6
2.2.1 Seismograph 6
2.2.2 Seismic Waves 7
2.2.2.1 Body Waves 7
2.2.2.1.1 P wave (body wave) 8
2.2.2.1.2 S wave (body wave) 8
2.2.2.2 Surface Waves 9
2.2.2.2.1 Love wave (surface wave) 9
2.2.2.2.2 Rayleigh wave (surface wave) 10
2.2.3 Methods for Determining Dynamic Properties of Soil 10
III
2.2.4 Measurement Scales of Earthquakes 16
2.2.4.1 Magnitude of An Earthquake 16
2.2.4.2 Intensity of an Earthquake 17
2.3 History of Earthquake Studies in Iraq 18
2.4 Effect of Earthquake 21
2.5 Soil-Structure Interaction 22
2.6 Kinematic Bending Moment 23
2.7 Piles behavior under earthquake action 27
2.8 Summary 34
Chapter Three: Data Base for Dynamic Soil Properties of Seismic Active
Zones in Iraq
3.1 Introduction 35
3.2 Resource of Data and Presentation 35
3.3 Geotechnical and Geophysical Parameters Investigated for Iraq Soils 37
3.4 Soil Parameters Evaluation 38
3.4.1 Field Testing 42
3.4.1.1 Standard Penetration Test (S.P.T) 42
3.4.1.2 Field density (Core Cutter Test) 44
3.4.2 Laboratory Testing 45
3.4.2.1 Soil Classification ( Sieve Analysis and Hydrometer ) 45
3.4.2.2 Direct Shear Test 45
3.4.2.3 Unconfined Compression Test 45
3.4.2.4 Unconsolidated-Undrained Triaxial Compression Test (UU Test) 45
3.4.2.5 Consolidated Undrained Triaxial Compression Test (CU Test) 46
IV
3.4.2.6 Consolidated Drained Triaxial Compression Test (CD Test) 46
3.4.3 Geophysical Investigation 47
3.4.3.1 Cross-hole Test 47
3.4.3.2 Down-hole Test 48
3.5 Rayleigh damping constants α and β 48
3.6 Earthquakes in Iraq 50
3.6.1 Seismo Signal Program 54
3.6.2 Seismic Zones in Iraq 55
3.6.3 Site Soil Seismic Classification 56
3.6.4 Site Soil Seismic Classification of Iraq Soils 58
3.7 Conclusions from the collected database 58
Chapter Four: Finite Element Dynamic Modeling and verification Problems

4.1 General 60
4.2 Equations of Motion 60
4.2.1 External Force 60
4.2.2 Earthquake Ground Motion 62
4.3 PLAXIS 3D 2013 Program 63
4.3.1 Drainage Type 64
4.3.3 PLAXIS 3D 2013 Models 66
4.3.3.1 Linear Elastic model (LE) 66
4.3.3.2 Mohr- Coulomb Model (MC) 66
4.3.3.2.1 Formulation of Mohr-Coulomb Model 67
4.3.3.3 Hardening Soil model with small-strain stiffness (HSsmall) 69
4.3.4 Soil Elements 69
4.3.4.1 10-Node Tetrahedral Element 69
V
4.3.5 Embedded Pile Element 71
4.4 Model Verification 72
4.5 Study of Kinematic Bending Moment of Pile under Seismic Motion 72
4.5.1 Overview and Model Information 73
4.5.2 Finite Element Modeling of Problem using PLAXIS 3D 2013 74
4.5.2.1 Dimensions and Boundary Conditions of the Model 75
4.5.2.2 Soil and Interface Modeling 75
4.5.2.3 Pile Modeling 76
4.5.2.4 Earthquake Modeling 76
4.5.2.5 Mesh Generation 77
4.5.2.6 Performing Calculations 77
4.5.2.7 Analysis Results 78
4.6 Free Vibration and Earthquake Analysis of a Building 80
4.6.1Geometry Model 80
4.6.2 Soil Model 81
4.6.2 Structural Model 82
4.6.3 Loading Model 83
4.6.5 Performing Calculations 83
4.6.6 Veiwing The Results 84
Chapter Five: Parametric Study

5.1 Introduction 87
5.2 Seismic Behavior of Pile in Iraq Soils 87
5.2.1 Geometry Model 87
5.2.2 Soil Modeling 87
5.2.3 Pile and Point Load Modeling 88
VI
5.2.4 Earthquake Modeling 89
5.2.5 Boundary Conditions of the Model 89
5.2.6 Mesh Generation 90
5.2.7 Performing Calculations 90
5.3 Influence of Soil Dynamic Parameters on the Behavior of Pile 91

5.4 Parametric Study 99
5.4.1 Effect of Pile Length Lp 102
5.4.2 Effect of Pile Diameter Dp 105
5.4.3 Effect of Modulus of Elasticity Ep 107
5.4.4 Effect of Earthquake Acceleration 109
Chapter Six: Conclusions and Recommendations

6.1 Introduction 112
6.2 Conclusions 112
6.3 Recommendations 115
References 116
Appendix A A-1
VII
NOTATIONS AND SYMBOLES
[C] Damping matrix.

[c] The modal damping matrix.
[K] The stiffness matrix.
[M] The mass matrix.
a The acceleration of earthquake.
amax Peak ground acceleration.
c Cohesion
ci The coefficient of viscous damping.
cu (su) Undrained shear strength .
D The distance of the recording station.
Dp Diameter of pile.
E Young's modulus
Ed Dynamic modulus of elasticity
Ep Modulus of elasticity for the pile
Eref 50 Secant stiffness in standard drained triaxial test.
Eref oed Tangent stiffness for primary oedometer loading.
Erefur Unloading and reloading stiffness.
fc' The compressive strength of concrete at 28 days.
FD Damping force.
FI Inertia force.
Fmax Base resistance.
FR Restoring force.
G Shear modulus (or rigidity)
G0ref The small-strain shear modulus.
VIII
Gd Dynamic shear modulus
H Depth of soil layer.
Ip Moment of inertia for the pile
K Bulk modulus (or incompressibility)
Lp Length of pile.
m Power of stress level dependency of stiffness
ML Richter magnitude.
N No. of blows for standard penetration test (SPT).
Ni Shape function matrix.
Ni The shape function.
Npile The bearing capacity of the pile.
P The total force.
PGA peak ground acceleration.
PGV peak ground velocity.
qu Unconfined compressive strength.
Tbot,max Pile bottom resistance.
Ttop,max Pile top skin resistance.
uʹʹ The acceleration.
u The displacement.
uʹ The relative velocity.
ug'' Earthquake acceleration.
up The displacement of the pile.
us The displacement of soil.
ux Horizontal displacement in x-direction.
uy Horizontal displacement in y-direction.
uz Vertical displacement in z-direction.
IX
v The nodal displacement vector.
Vp Compression wave velocity
Vs Shear wave velocity
Vs,30 Average shear wave velocity in the upper 30 m of soil.
α The mass-proportional coefficient.
β The stiffness-proportional coefficient.
γ0.7 The strain level at the shear modulus is reduced to about 70% of G0ref.
γdry Dry unit weight.
γp Density of pile material.
γsat Saturated unit weight
γunsat Unsaturated unit weight
γwet Wet unit weight.
εe The elastic part of strain .
εp The plastic part of strain.
ζi Damping ratio.
ξ, η and ζ Local coordinates.
ρ Density.
σ1 The major principle stress.
σ3 The minor principle stress.
τf The shear stress at failure .
υ Poisson's ratio .
υp Poisson's ratio for pile.
ϕ Friction angle.
ψ Dilatancy angle.
ωi Damping ratio.
X
LIST OF TABLES
Table Title Page

2.1 UBC site classification (after Hasan, 2011). 15
2.2 Richter magnitude and its effects (after Kihampa ,2010). 16
2.3 Modified Mercalli intensity scale (after U.S. Geological Survey 17
document, 1989)
2.4 Locations and magnitudes of the four earthquakes (after Mohammed 21
et. al., 2014).
3.1 The available projects in some locations of Iraq with their site areas 36
and symbols.
3.2 Soil properties in different locations of Iraq. 39
3.3 Correlations with N values of cohesionless soils (after Bowles, 1997) 43
3.4 Correlations between unconfined compressive strength qu- N values 44
(after Terzaghi and Peck, 1967)
3.5 Classification of the distance ,magnitude and intensity of the four 54
earthquakes hit Ali Al-Gharbi during the latest five years.
3.6 Site soil classification (after PISC, 2013 ). 56
3.7 Site class and soil types (after FEMA, 2010). 57
3.8 Ground Types classification (after Eurocode 8, 2004). 57
3.9 Iraq site soil classification. 58
4.1 4-point Gaussian integration for 10-node tetrahedral element (after 71
PLAXIS 3D Manual, 2013).
4.2 Input soil parameters. 76
4.3 Ground type according to (Eurocode 8, 2004). 76
4.4 Model parameters and soil properties of HS small model (after 81
PLAXIS 3D Manual, 2013)
4.5 Model parameters and soil properties of Mohr –Coulomb model 82
4.6 Structural plates properties (after PLAXIS 3D Manual, 2013). 82
4.7 Material properties of node-to-node anchor (after PLAXIS 3D 83
Manual, 2013)
5.1 Material properties of the embedded pile. 88
A.1 Allowable bearing capacity of single pile A-5
XI
LIST OF FIGURES
Figure Title Page
2.1 Seismograph instrument. 7
2.2 Primary wave (after Jasim, 2010). 8
2.3 Secondary wave (after Jasim, 2010). 9
2.4 Love wave (after Jasim, 2010). 10
2.5 Rayleigh wave (after Jasim, 2010). 10
2.6 Classification of dynamic methods for obtaining shear modulus 11
(after Sitharam et al., 2004).
2.7 Flowchart of dynamic parameters used in foundation design. 12
2.8 Location of seismic profiles (after Khorshid et. al., 2006). 14
2.9 Map showing the spatial distribution of the NISN and ISN (Iraq 15
Seismographic Network) stations (after Ahmed and Aziz, 2013).
2.10 (a) Location Map of the Studied Area. (b) The Epicentral 19
Distribution of earthquakes with Mw ≥ 3 in Western Desert During
1900-2004 (after Al-Heety, 2010).
2.11 Map of the study area (after Abd Alridha and Jasem, 2013). 19
2.12 Comparison between bending moments predicted by analytical 26
solutions and those evaluated by the finite element analyses for
subsoils (Vs1 = 100 m/s) under the action of Tolmezzo (1976) and
Norcia Umbra(1997) earthquakes (after Maiorano et. al., 2009).
2.13 Experimental and theoretical results of maximum kinematic bending 27
moment at the interface in free head pile tests (STU= Sturno-A000,
TMZ=Tomezzo-A270) (after Dihoru et. al., 2010).
2.14 (a) Centrifuge test model and measuring instruments. (b) Test cases 28
(after Miyamoto Y., 2000).
2.15 Maximum bending moments in the pile versus sand density (after 29
Ahmadi and Ehsani, 2008).
2.16 Maximum shear forces in the pile versus sand friction angle (after 29
2.17 (a) Depth of the pile vs bending moment. (b) Depth of the pile vs 30
displacement (after Muthukkumaran and Subha, 2010).
XII
2.18 (a) Pile passing through liquefied layer. (b) Pile deflections in 31
liquefied soils considering various ground motions –Free headed
pile (after Phanikanth et. al., 2011).
2.19 Pile failure mechanisms (after Meyersohn, 1994). 32
2.20 (a) Prototype 15-story building supported by end-bearing pile 33
foundation; (b) prototype 10-story building supported by end-
bearing pile foundation; (c) prototype 5-story building supported by
end-bearing pile foundation (after Hokmabadi et. al., 2014).
3.1 Seismic zones and projects locations in Iraq. 37
3.2 Relation Between Number of Blowes Per Foot in Standard 43
Penetration Test and Velocity of Shear Waves (after department of
defense handbook MIL-HDBK-1007/3, 1997).
3.3 Standard Penetration Test (after Clayton, 1995). 43
3.4 Cross hole test procedure (after Davis & Schultheiss 1980). 47
3.5 Down hole test procedure (after Davis & Schultheiss 1980). 48
3.6 Variation of the viscous damping ratio ζ with frequency (after Lanzo 50
et. al. , 2003).
3.7 Location of the highest earthquakes hit Ali Al-Gharbi for the latest 51
five years recorded by the Iraqi Seismological Network (ISN),
Badrah.
3.8 Earthquake reading hit 20.72 km from Ali-Al Gharbi recorded by 52
the Iraqi Seismological Network (ISN) (after Ali, 2014).
3.9 Earthquake reading hit 13.2 km from Ali-Al Gharbi recorded by the 52
Iraqi Seismological Network (ISN) (after Ali, 2014).
3.10 Earthquake reading hit 11 km from Ali-Al Gharbi recorded by the 53
3.11 Earthquake reading hit 12.38 km from Ali-Al Gharbi recorded by 53
the Iraqi Seismological Network (ISN) (after Ali, 2014).
3.12 Seismogram of the strongest earthquake hit Ali Al-Gharbi. 54
3.13 Seismic Zone Map of Iraq (Iraqi Seismic Code Requirements for 55
Buildings, 1997).
4.1 Free Body Diagram of Single Degree of Freedom System (after 61
Chopra, 2011).
4.2 Pile subjected to earthquake ground motion. 63
XIII
4.3 Basic idea of an elastic perfectly plastic model (after PLAXIS 3D 67
Manual, 2013)
4.4 Mohr- Coulomb´s criteria of failure in two dimensions (after 68
Brinkgreve et al, 2013)
4.5 The failure surface of Mohr-Coulomb's model in principal stress 68
space for cohesionless soil (after Brinkgreve et al, 2013).
4.6 Local numbering and positioning of nodes (•) and integration points 70
(x) of a 10-node tetrahedral element (after Brinkgreve et al, 2013).
4.7 Illistration of the embedded beam element denoted by the solid line , 71
the blank grey circles denote the virtual nodes of the soil element
(after PLAXIS 3D Manual, 2013).
4.8 Shape function for a 3-node line element (after PLAXIS 3D 72
Manual, 2013).
4.9 Reference scheme model (a) Soil model, (b) Typical 2D model for 74
FE Analysis (after Khari, et. al., 2014).
4.10 Acceleration time history and response spectra at the bedrock roof 74
(after Khari, et. al., 2014)
4.11 (a) 3D Soil profile model. (b) embedded pile model and earthquake 75
prescribed displacement at bedrock of the model using PLAXIS 3D
2013.
4.12 Earthquake acceleration-time records. 77
4.13 Mesh generation of 3D model. 77
4.14 Model of 2D present study by PLAXIS 3D 2013. 78
4.15 Comparison between PLAXIS 3D results of present study and 79
results of 2D Khari et. al., (2014) and simplified approaches' results.
4.16 Geometry of the model (after PLAXIS 3D Manual, 2013). 81
4.17 Earthquake data (after PLAXIS 3D Manual, 2013) 83
4.18 Names of the selected points. 84
4.19 Time history of the displacements of point (A) at the top of the 85
building due to earthquake for HS small model and Mohr-Coulomb
model with and without damping.
4.20 The deflected shape for HS small model and Mohr-Coulomb model 86
with and without damping.
XIV
5.1 (a) Geometry and soil layers model (b) Embedded pile, point load 88
and the prescribed displacement of M5 site in Baghdad.
5.2 Acceleration – time records of earthquake hit Ali Al-Garbi in 89
Missan on April 20,2012 during 60 seconds.
5.3 Mesh generation for M5 site. 90
5.4 Bending moment diagrams of pile for North zone. 93
5.5 Bending moment diagrams of pile for Middle zone. 93
5.6 Bending moment diagrams of pile for Western south zone. 94
5.7 Bending moment diagrams of pile for Eastern south zone. 94
5.8 Bending moment diagrams of pile for South zone. 95
5.9 Bending moment diagram of single pile without superstructure 95
under seismic excitation (a) Kinematic bending. (b) Liquefaction-
induced bending (after Mylonakis and Nikolaou, 2002).
5.10 Horizontal displacement of pile per diameter with depth for North 96
zone.
5.11 Horizontal displacement of pile per diameter with depth for Middle 97
zone.
5.12 Horizontal displacement of pile per diameter with depth for Western 97
south zone.
5.13 Horizontal displacement of pile per diameter with depth for Eastern 98
south zone.
5.14 Horizontal displacement of pile per diameter with depth for South 98
zone.
5.15 Horizontal displacement of soil layers. 100
5.16 Plastic points of the model (a) three dimensional model. (b) 100
longitudinal cross section of the model at 15 m in the y-axis.
5.17 Maximum shear stresses for the soil cross section at 15m in the y- 101
axis.
5.18 The horizontal displacement ux for node points (A, B, C and D) with 102
dynamic time.
5.19 Bending moment diagrams using different pile lengths. 103
5.20 Horizontal displacement as a percentage of pile diameter using 104
different pile lengths.
XV
5.21 Vertical displacement of pile head as a percentage of the pile 104
diameter for different pile lengths.
5.22 Bending moment diagrams using different pile diameters. 105
5.23 Maximum bending moment for different pile diameters. 106
5.24 Horizontal displacement of pile as a percentage of 1m diameter 106
using different pile diameters.
5.25 Vertical displacement of pile head as a percentage of 1m diameter 107
for different pile diameters.
5.26 Bending moment diagrams using different pile modulus of 108
elasticity.
5.27 Maximum bending moment for different pile stiffness. 108
5.28 Horizontal displacement as a percentage of pile diameter using 109
different pile modulus of elasticity
5.29 Vertical displacement of pile head as a percentage of the pile 109
diameter for different pile stiffness.
5.30 Bending moment diagrams for earthquake acceleration. 111
5.31 Horizontal displacement of pile as a percentage of diameter using 111
different earthquake acceleration.
A.1 The relationship between Ø and Nq. A-4
LIST OF PLATES
Plate Title Page
2.1 Shear stack installed on the earthquake simulator (after Dihor et.al., 27
2010).
XVI
CHAPTER ONE Introduction
CHAPTER ONE
Introduction
1.1 General
Observation of structural performance of buildings during an earthquake can
clearly identify the strong and weak aspects of the design, as well as the desirable
qualities of materials and techniques of construction and site selection. The study of
damage therefore provides an important step in the evolution of strengthening measures
for different types of buildings.
As the soil is the only media for the earthquake waves to propagate from the
focus to the structure , it has a great effect on the earthquake severity. Also the type of
soil has a major effect on the wave propagation, but the important effect is the soil
structure interaction in which the response of the soil influences the motion of the
structure and the motion of the structure influences the response of the soil is termed as
Soil-Structure Interaction (SSI). In this case neither the structural displacements nor the
ground displacements are independent from each other. SSI has increasingly attracted
the interest of researchers and engineers in the fields of wave mechanics and soil
dynamics. Piles are generally used to carry the vertical loads from the super structure
but sometimes to withstand the effect of lateral load ( Maste et.al., 2014).
Piles are structural members used to transfer the super-structure loads to the
underlying soil strata. They act either as a compression or tension members and
sometimes with bending stresses. As the foundation is the part of the structure which is
responsible of transmitting earthquake loads from the soil to the whole structure, it was
recognized that the earthquake response of the structure must include the dynamic
interaction of the structure with the foundation. Analysis of pile foundations is an
important topic of research for geotechnical engineers for several decades. It is more
important when the analysis has to be carried out under earthquake conditions
(Mukhopadhyay et. al., 2008).
In the recent years, there is a dramatic progress in the development of theories
for dynamic analysis of piles. The rapid development of pile analysis is prompted by
the growing use of pile foundations in traditional areas. As well as it’s used as a deep
1
foundation for building, or as a machine foundations and their large scale use in civil
engineering applications such as nuclear power plants, offshore towers and other giant
projects. Many methods have been used to examine the foundation behavior under
dynamic loadings; they are basically classified as experimental and theoretical
approaches. The experimental approach includes models and field studies on existing
foundations while the theoretical approach includes analytical and numerical solutions
(Al-Wakel et. al., 2014).
Damage due to dynamic loading (e.g. earthquake strong motions) is
substantially influenced by the response of soil deposits which is governed by the
dynamic soil properties. Comprehending the dynamic properties of soils aid to predict
and/or analyze the dynamic behavior. Dynamic soil properties namely shear wave
velocity, variation of stiffness or modulus reduction and material damping with strain
levels, and liquefaction susceptible parameters are the primary input parameters for
various dynamic studies and investigations. The determination of dynamic soil
properties is an utmost critical and important aspect of geotechnical earthquake
engineering problems. In general soil properties depend on different state parameters
such as the state of stress, void ratio, confining stress and water content, stress history,
strain levels, and drainage condition. Apart from the influence of the above mentioned
parameters, dynamic soil properties are significantly influenced by the dynamic
amplitude and frequency of the applied load. Hence determination/estimation of the
dynamic soil properties requires the consideration of all the above-mentioned
influencing parameters. Dynamic soil properties can be determined from different field
and/or laboratory tests such as cross hole test, down hole test, seismic reflection,
seismic refraction, triaxial test, cyclic triaxial test, cyclic sample shear test, shaker table
test …etc. (Kumar et. al., 2013).
1.2 Problem Statement

Predicting the behavior of piles and pile groups during earthquakes still remains
a challenging task to geotechnical engineers. In most of the published results on the
dynamic analysis of pile foundations, soil has been considered as a linear elastic
material. Material linearity permits analyses in the frequency domain where the
2
principle of superposition can be used to superimpose loading at different frequencies.

However, under strong seismic excitation, nonlinearity of the soil medium and
separation at the soil-pile interface can have significant influence on the response of the
pile. Therefore, the response analysis should be carried out in the time domain in order
to properly incorporate soil nonlinearity.
Tectonically Iraq is located in a relatively active seismic zone at the
northeastern boundaries of the Arabian Plate .The corresponding Zagros - Tauros Belts
manifest the subduction of the Arabian plate into the Iranian and Anatolian Plates .The
seismic history reveals annual seismic activity of different strength. The north and
northeastern zones depicts the highest seismic activity with strong diminution in the
south and southwestern parts of the country (Abd Alridha and Jasem, 2013).
The territory of Iraq, although not directly located on a dense cluster of recent
earthquake epicenters; but the geodynamic configurations show a medium to high
seismic risk. This will be coupled with the increasing vulnerability of the major highly
populated cities. The state of seismological research, seismic monitoring, and seismic
hazard awareness have seen better times during the last two decades (Alsinawi and Al-
Qasrani, 2003).
Dynamic properties play a vital role in the design of structures under seismic
loads. Evaluation of dynamic soil properties by field tests has a number of advantages,
as these tests do not require sampling that can alter the stress and structural conditions
in soil specimens. Further, the tests measure the response of relatively large volumes of
soil. However, these field tests can be again classified based on the range of magnitude
of strain as low-strain and high-strain tests. Low-strain tests are based on the theory of
wave propagation in the materials. Some of the low-strain field tests are seismic
reflection test. seismic refraction test, suspension logging test, steady-state vibration or
rayleigh wave test, spectral analysis of surface wave test, seismic cross-hole test,
seismic down-hole test and seismic cone test. The field tests which are generally used
in Iraq for determining the dynamic properties of soils used in designing purposes are
the seismic cross-hole and down-hole tests.
3
1.3 Scope of the Study

The main objectives of this study is to prepare a database for the dynamic
properties of Iraqi different soils using cross-hole and down-hole tests, then use it to
investigate numerically the seismic behavior of piles foundation under the influence of
an actual seismic data in Iraq using the finite element method. This will require getting
information for dynamic soil properties of different seismic active zones in Iraq from
available geophysical and geotechnical soil investigation reports collected from
engineering consulting bureaus of Al-Nahrain, Baghdad and Technology universities
together with the National Center of Construction Laboratories and Research
(NCCLR) and other geophysical investigation companies from private sector.
Furthermore, using the seismic records for the strongest earthquake occurred in Iraq
during the last five years from the available sources.
In the numerical study, the 3-D analyses are performed using finite element
computer program PLAXIS 3D 2013 which is capable of modeling the soil-pile
system, embedment pile element (friction or end-bearing) and seismic behavior of the
system using the dynamic properties and earthquake data.
Example of model prediction and accuracy of finite element formulation will be
given. Then the analysis of 3-D soil-pile system under earthquake action using the
database prepared will be carried out taken into consideration the influence of some
parameters on the dynamic behavior of the pile, such as pile length, diameter and
stiffness as well as the influence of the earthquake acceleration-time records.
1.4 Thesis Layout

This thesis contains six chapters:
Chapter one: Includes a general introduction to piles and dynamic soil properties due
to earthquakes as well as a brief description of seismic activity in Iraq. In addition to a
general description for the main objectives of this study.
Chapter two: Includes a brief description of earthquakes, seismic waves and their
measurements, soil structure interaction and kinematic bending moment. And contains
history for earthquake studies in Iraq. Also, provides a relevant review of the available
studies on piles response due to earthquake action.
4
Chapter three: Presents the database for static and dynamic properties of soils for
seismic active zones in Iraq evaluated from field and laboratory tests results of
available geophysical and geotechnical investigation reports. And, includes the latest
Iraq seismic records collected from Iraqi Seismological Network (ISN).
Chapter four: Contains a finite element dynamic modeling using PLAXIS 3D 2013
program and performs two verification problems to study the validity of numerical
analysis of a soil-pile system under earthquake loading and the validity of Mohr-
Coulomb model in simulating structures under earthquake action.
Chapter five: Investigates the bending moment diagram and the horizontal deflected
shape for single pile embedded in different soils for seismic active zones in Iraq using
PLAXIS 3D 2013 program. And includes a parametric study for the effect of pile
length, diameter and stiffness together with the influence of earthquake acceleration on
the dynamic behavior of a soil-pile system under earthquake loadings.
Chapter six : summarizes the main conclusions drawn from the present study and
includes recommendations for further research works.
5
CHAPTER TWO Litrature Review
CHAPTER TWO
Literature Review
2.1 Introduction
In this chapter a review of the available studies for earthquakes and dynamic
behavior of piles and surrounding soil in Iraq and the world is made.
In order to understand the effect of earthquake on soil and pile behavior, basic
information of earthquake is studied including geophysical measurements of seismic
waves and determination of dynamic soil properties. Soil-pile behavior under seismic
excitation is analyzed due to soil structure interaction, kinematic bending moment and
soil liquefaction (for cohesionless soils) using different computer programs.
2.2 Earthquake
Earthquakes are one of the most destructive of natural hazards. Earthquake
occurs due to sudden transient motion of the ground as a result of release of elastic
energy in a matter of few seconds. The impact of the event is most traumatic because it
affects large area, occurs all on a sudden and unpredictable. Earthquakes can cause
large scale loss of life and property and disrupts essential services such as water supply,
sewerage systems, communication and power, transport etc. Earthquakes not only
destroy villages, towns and cities but the aftermath leads to destabilize the economic
and social structure of the nation (Soni et al, 2012).
Geotechnical earthquake engineering can be defined as that subspecialty within
the field of geotechnical engineering which deals with the design and construction of
projects in order to resist the effects of earthquakes. Geotechnical earthquake
engineering requires an understanding of basic geotechnical principles as well as
geology, seismology, and earthquake engineering. In a broad sense, seismology can be
defined as the study of earthquakes (Day, 2012). This would include the internal
behavior of the earth and the nature of seismic waves generated by the earthquake
(Kumar, 2008).
2.2.1 Seismograph
A seismograph is an instrument that records, as a function of time, the motion of
the earth’s surface due to the seismic waves generated by the earthquake, seismograph
6
shown in Figure (2.1). The actual record of ground shaking from the seismograph,
known as a seismogram can provide information about the nature of the earthquake. A
seismograph records is presented in three types of plots (Day,2012) :
1. Acceleration versus time.
2. Velocity versus time.
3. Displacement versus time.
Figure (2.1) Seismograph instrument.
2.2.2 Seismic Waves

Earthquakes generate elastic waves when one block of material slides against
another, the break between the two blocks being called a ‘fault’. If the equilibrium of a
solid body like the earth is disturbed due to fault motion resulting from an earthquake,
seismic (elastic) waves are transmitted through the body in all directions from the
focus. Earthquakes radiate waves with periods of tenths of seconds to several minutes.
Rocks behave like elastic solids at these frequencies. Elastic solids allow a variety of
wave types and this makes the ground motion after an earthquake quite complex
(Tapan , 2009).
2.2.2.1 Body Waves

The body waves propagate within a body of rock. The faster of these body
waves is called Primary wave (P-wave), or longitudinal wave or compressional wave,
and the slower one is called Secondary wave (S-wave) or shear wave (Kayal ,2007).
7
2.2.2.1.1 P wave (body wave)

The P wave is also known as the primary wave, compressional wave, or
longitudinal wave, as shown in Figure (2.2). It is a seismic wave that causes a series of
compressions and dilations of the materials through which it travels. The P wave is the
fastest wave and is the first to arrive at a site. Being a compression-dilation type of
wave, P waves can travel through both solids and liquids. Because soil and rock are
relatively resistant to compression- dilation effects, the P wave usually has the least
impact on ground surface movements (Day, 2012).
The velocity of compressional wave Vp is related to the elastic constants as in
Equation (2.1) (Doyle, 1995) :
Vp = [ ( K + 4 / 3 G) / ρ ]½ (2.1)
where:
Vp= P-wave velocity
K = Bulk modulus (or incompressibility)
G = Shear modulus (or rigidity)
ρ = Density
Figure (2.2) Primary wave (after Jasim, 2010).
2.2.2.1.2 S wave (body wave)

The S wave is also known as the secondary wave, shear wave, or transverse
wave as shown in Figure (2.3). The S wave causes shearing deformations of the
materials through which it travels. Because liquids have no shear resistance, S waves
can only travel through solids. The shear resistance of soil and rock is usually less than
the compression-dilation resistance, and thus an S wave travels more slowly through
the ground than a P wave. Soil is weak in terms of its shear resistance, and S waves
typically have the greatest impact on ground surface movements (Day,2012).
8
The relation between S wave velocity Vs, the elastic constants and density is given as
(Doyle, 1995):
Vs = [ ( G / ρ ) ] ½ (2.2)
The velocity ratio (Vp/Vs) is found by comparing the equations (2.1) and (2.2):
Vp/Vs =[ ( K+ 4 / 3 G)/G] ½ = [(K/G)+4/3] ½ (2.3)
Vp/Vs = [(1- υ)/1+ υ)] ½ (2.4)
where:
υ = Poisson’s ratio
For most consolidated rock Vp/Vs approximately equals to 3. In this context, it
may be mentioned that amplitudes of S-waves are generally five times larger than those
of P-waves. Also, the periods of S-waves are longer, at least by a factor of 3, than those
of P-waves due to differences in wave propagation velocity (Kayal ,2007).
Figure (2.3) Secondary wave (after Jasim, 2010).
2.2.2.2 Surface Waves

When the two types of body wave reach the surface of the earth, an interesting
change occurs in the behavior of the waves. The combination of the two types of wave
in the presence of the surface leads to other two types of waves, Rayleigh waves and
Love waves (Tapan,2009), which are important for geophysics.
2.2.2.2.1 Love wave (surface wave)

Love waves are analogous to S waves in that they are transverse shear waves that
travel close to the ground surface (Yeats et.al.,1997), as shown in Figure (2.4).
9
Figure (2.4) Love wave (after Jasim, 2010).
2.2.2.2.2 Rayleigh wave (surface wave)

Rayleigh waves have been described as being similar to the surface ripples
produced by a rock thrown into a pond as shown in Figure (2.5). These seismic waves
produce both vertical and horizontal displacement of the ground as the surface waves
propagate outward.
Figure (2.5) Rayleigh wave (after Jasim, 2010).
Generally, there is no need for the engineer to distinguish between the different
types of seismic waves that could impact the site. Instead, the combined effect of the
waves in terms of producing a peak ground acceleration amax is of primary interest.
However, it is important to recognize that the peak ground acceleration will be most
influenced by the S waves and, in some cases, by surface waves.
2.2.3 Methods for Determining Dynamic Properties of Soil

The geotechnical engineering design of foundations subjected to dynamic
loading requires the determination of dynamic shear modulus of elasticity, which is
achieved by either laboratory or field testing (Sitharam et al., 2004) as shown in Figure
(2.6).
- Laboratory Testing
A small sample of soil is to be tested under controlled displacement, and it is
considered as economical process. Laboratory testing is classified into Low-Strain
Tests and High-Strain Tests, for the first method a very few laboratory tests are
01
available, Resonant Column is the most popular testing procedure commonly used for
determining dynamic soil properties at low strain levels. There are different versions of
this test with different end conditions for samples. For the second method several
devices are developed to determining strain dependent dynamic properties of soil. They
are monotonic dynamic triaxial test , cyclic triaxial test, cyclic sample shear test, shaker
table test and ultrasonic test.
Figure (2.6) Classification of dynamic methods for obtaining shear modulus(after

Sitharam et al., 2004).
- Field Testing
In order to evaluate the dynamic properties of soil the seismic wave velocities are
measured using geophysical techniques. The field tests has a number of advantages
over laboratory tests , as these tests don’t require sampling that can cause changes in
stress and structural conditions of soil specimen, and these tests are applied over a large
volumes of soil. The field tests can be classified just like the laboratory tests into Low-
Strain Tests and High-Strain Tests, the strain range in the first method is (below
0.001%) not large enough to induce significant non-linear non-elastic stress strain
behavior, the low-strain tests are based on the theory of wave propagation in the
materials. Some of the low-strain field tests are either surface vibration tests like
seismic refraction test , seismic reflection test, multi-channel analysis of surface waves
and refraction micro-tremor, or seismic tests like cross-hole test , up-hole test , down-
00
hole test and seismic cone test. In the second method the soil behavior is considered as
elasto-plastic and the Standard Penetration Test (SPT) and Cone Penetration Test
(CPT) are of particular importance to measure high strain characteristics of soil
(Sitharam et al., 2004).
In this study, cross-hole test and down-hole test will be considered. These test
methods are limited to the determination of horizontally traveling compression (P) and
shear (S) seismic waves at test sites consisting primarily of soil materials (as opposed
to rock). They are preferred test methods intended for use on critical projects where the
highest quality data must be obtained is included. The theory of seismic method is
based on fact that the velocity at which seismic wave travels through materials such as
soil and rock varies with the elastic properties of the material. Measurements are made
by generating a seismic disturbance at some points on the ground surface and
measuring the required time for the disturbance to travel from the source. The seismic
cross-hole method provides a designer with information pertinent to the seismic wave
velocities of the materials. This data may be used as input into static/dynamic analyses
as shown in Figure (2.7). The evaluation of shear modulus (G), Young’s modulus (Ed) ,
and Poisson’s ratio (υ), can be expressed by the following equations:
[ ] (2.5)
G = ρ Vs 2 (2.6)
Ed = 2 G ( 1+υ ) (2.7)
Figure (2.7) Flowchart of dynamic parameters used in foundation design.

01
Many Iraqi researchers studied the seismic wave’s measurements of Iraqi soils,
Al-Damluji and Salih (2006) investigated soil – pore fluid behavior of a silo
under an earthquake loading (El-Centro, California, May 18, 1940 earthquake is
applied). To predict the response of the silo with the soil surrounding it, ‘the linear-
elastic constitutive model’ is adopted with soil properties; shear modulus and damping
ratio; are strains and cycle independent. Two computer programs (DSMA) and
(MSC/NASTRAN) are used for predicting and analyzing the model. The programs are
based on geophysical values (such as primary velocity (Vp), shear velocity (Vs),
modulus of elasticity (E), mass density (ρ), shear modulus (G) and damping ratio (ξ)).
The values used for (DSMA) program were obtained from field test results for the soil
under a silo located in Kirkuk, Iraq. For the (MSC/NASTRAN) program uses input
values obtained from conventional laboratory tests.
From the two aforementioned analyses, comparisons between the results of the
relevant two programs are made. Though program “MSC/NASTRAN” visualizes a
realistic behavior of the silo under dynamic loading, due to full response results are
expressed for each node, the Dynamic Stiffness Matrix Analyses program (DSMA)
gives only the maximum value for the horizontal and vertical displacements at that
node. Despite of that, program DSMA relies on realistic values of geophysical tests
obtained from the field directly. The results show excellent agreement between the
results. The agreement in this study turns out to be more than 95% close between the
two algorithms. The easiness through which geophysical field tests are conducted, the
simplicity of carrying out the required calculations and the reliability of the results
makes the dynamic stiffness matrix analysis method (DSMA) highly recommended. It
can give an excellent directive about the response of structures resting on soils and
subjected to dynamic loads.
Khorshid et. al. (2006) investigated the site of hostel complex inside Basrah
university, southern of Iraq and evaluated P and S-waves using seismic refraction
techniques as an available tool for engineering purposes. Eight seismic profiles for
either P and S-waves had been chosen as shown in Figure (2.8), and carried out by the
use of five impacts, in order to delineate layers thicknesses and depth of water table.
Dynamic elastic modulii were also calculated depending upon the velocities of P and S-
01
waves of these layers and its densities. Accordingly, three shallow subsurface soil
layers were found. Their mean thicknesses are ranged between (2.15-2.45) m, (17.65-
18.4) m below ground surface for the top and first layers respectively. On the other
hand, mean water table seems to be at (2.3) m depth and the mean dynamic elastic
constants are ranged between (Dynamic Bulk Modulus = (0.194-7.352×103) MPa,
Dynamic Shear Modulus= (0.145-2.994×103) MPa, Dynamic Young Modulus = (0.364-
7.385×103) Mpa and Poisson's Ratio = (0.19-0.35)). It has been concluded that there
are very good matching between the depths that are determined by seismic refraction
technique and the drilled borehole which clearly shows the contacts between the three
layers. And it is appeared that there is a proportional relationship between the dynamic
elastic Moduli.
Figure (2.8) Location of seismic profiles (after Khorshid et. al., 2006).
Hasan (2011) computed the seismic velocities (P and S Waves) from previous
data of two sites, Karbala and Baiji sites soils,. In Karbala site , four profiles were used
to evaluate the geotechnical properties of soil and determine weak zones, each profile
has three boreholes: one for source and the two others for receivers. The depths of
01
boreholes were (12-15m). In Baiji site, three profiles. The depths of boreholes were
(17-20m).In Karbala site soil, the elastic moduli and the geotechnical properties were
computed. Soil of profiles around foundation is classified as soft rock (Sc) depending
on classification of Federal Emergency Management Agency, FEMA (1997) and
Uniform Building Code, UBC (1997) as shown in Table (2.1) and for soil of profiles
under foundation is classified as rock (SB). For Baiji site, the geotechnical properties
and elastic module show that the materials are moderately competent materials but of
one borehole at depths (16-20m) are competent materials. Site soil is classified as very
dense soil (Sc).
Table (2.1) UBC site classification (after Hasan, 2011).
Ahmed and Aziz (2013) investigated four different body wave phases from
events recorded by eight modern broad-band seismographic stations (North Iraq
Seismographic Network NISN) installed in northeastern Iraq as shown in Figure (2.9).
Figure (2.9) Map showing the spatial distribution of the NISN and ISN (Iraq
Seismographic Network) stations (after Ahmed and Aziz, 2013).
01
The analyses include identifying the P- and S-wave phases from different
azimuths and locating the events. The processed local and regional earthquakes which
have been recorded in the studied area were in the close proximity to the northeastern
border of the Arabian plate and occurred over a period between (2010-2012),
concluding that the overall seismicity of the studied area is influenced mainly by the
Zagros systems.
2.2.4 Measurement Scales of Earthquakes

There are two basic ways to measure the strength of an earthquake: (1) based on
the earthquake magnitude and (2) based on the intensity of damage. Magnitude
measures the amount of energy released from the earthquake, and intensity is based on
the damage to buildings and reactions of people.
2.2.4.1 Magnitude of an Earthquake

Earthquake magnitude or amount of energy released is determined by use of a
seismograph, and instrument that continuously records ground vibrations. A scale
developed by a seismologist named Charles Richter mathematically adjusts the
readings for the distance of the instrument from the epicenter. The Richter scale is
logarithmic. An increase of one magnitude signifies a 10-fold increase in ground
motion or roughly an increase of 30 times the energy ,see Table (2.2). Thus, an
earthquake with a magnitude of 7.5 releases 30 times more energy than one with a 6.5
magnitude, and approximately 900 times that of a 5.5 magnitude earthquake. A quake
of magnitude 3 is the smallest normally felt by humans. The largest earthquakes that
have been recorded under this system are 9.25 (Alaska, 1969) and 9.5 (Chile, 1960).
Table (2.2) Richter magnitude and its effects (after Kihampa ,2010).
Richter Magnitude Earthquake Effects
Less than 3.5 Generally not felt, but recorded.
3.4-5.4 Often felt, but rarely causes damage.
At most slight damage to well-designed buildings. Can cause
Under 6.0 major damage to poorly constructed buildings over small
regions.
Can be destructive in areas up to about 100 kilometers across
6.1-6.9
where people live.
Major earthquake. Can cause serious damage over larger
7.0-7.9
areas.
Great earthquake. Can cause serious damage in areas several
8 or greater
hundred kilometers across.
06
2.2.4.2 Intensity of an Earthquake

The intensity of an earthquake is based on the observations of damaged
structures and the presence of secondary effects, such as earthquake-induced
landslides, liquefaction, and ground cracking. The intensity of an earthquake is also
based on the degree to which the earthquake was felt by individuals, which is
determined through interviews (Day, 2012).
The scale currently used in the United States is the Modified Mercalli (MM)
intensity scale shown in Table (2.3). It was developed in 1931 by the American
seismologists Harry Wood and Frank Neumann. This scale, composed of 12 increasing
levels of intensity that range from imperceptible shaking to catastrophic destruction, is
designated by Roman numerals. It does not have a mathematical basis; instead it is an
arbitrary ranking based on observed effects (U.S. Geological Survey document, 1989).
Table (2.3) Modified Mercalli intensity scale (after U.S. Geological Survey
document, 1989).
Intensity Shaking Description of Damage
I Not Felt Not felt except by a very few under especially favorable conditions
Felt only by a few persons at rest, especially on upper floors of
II Weak buildings.
Felt quite noticeably by persons indoors, especially on upper
floors of buildings. Many people do not recognize it as an
III Weak earthquake. Standing motor cars may rock slightly. Vibrations
similar to the passing of a truck. Duration estimated.
Felt indoors by many, outdoors by few during the day. At night,
some awakened. Dishes, windows, doors disturbed; walls make
IV Light cracking sound. Sensation like heavy truck striking building.
Standing motor cars rocked noticeably.
Felt by nearly everyone; many awakened. Some dishes, windows
V Moderate broken. Unstable objects overturned. Pendulum clocks may stop.
Felt by all, many frightened. Some heavy furniture moved; a few
VI Strong instances of fallen plaster. Damage slight.
Damage negligible in buildings of good design and construction;
Very slight to moderate in well-built ordinary structures; considerable
VII
Strong damage in poorly built or badly designed structures; some
chimneys broken.
Damage slight in specially designed structures; considerable
damage in ordinary substantial buildings with partial collapse.
VIII Severe Damage great in poorly built structures. Fall of chimneys, factory
stacks, columns, monuments, walls. Heavy furniture overturned.
Damage considerable in specially designed structures; well-
designed frame structures thrown out of plumb. Damage great in
IX Violent substantial buildings, with partial collapse. Buildings shifted off
foundations.
Some well-built wooden structures destroyed; most masonry and
X Extreme frame structures destroyed with foundations. Rails bent.
07
2.3 History of Earthquake Studies in Iraq

The first seismological recording in Iraq was initiated in 1972 when the
Geology Department of the University of Baghdad initiated a mobile micro earthquake
monitoring survey of Iraq. The Iraqi seismological unit was initiated within the Iraqi
scientific research foundation in 1976. Since then, the Seismology Unit began the
establishment of the Iraqi Seismological Network (ISN), which was basically
composed of four main observatories. The coordinates of the stations are: Baghdad
Observatory (BHD), Mosul Observatory (MSL), Sulymania Observatory (SLY) , Rutba
Observatory (RTB), as shown in Figure (2.9). All stations were built and operational in
the early eighties except for Basrah station (Al-Salim and Al-Sinawi , 2006).
While it cannot prevent natural phenomena such as earthquakes, it can limit
their impacts by studying earthquakes effects on structures. And taking into account
these eccentric loadings generated from earthquakes in design of structural and
geotechnical projects. The records of earthquakes support the researchers with
important data to be used in their studies.
Al-Heety (2010) analyzed the seismicity of Iraqi western desert as shown in

Figure (2.10 a). During the period from 1900 to 2004, there occurred about 40 events
with magnitude Mw ≥ 3.0.The area was inactive before 1970.This may be attributed to
quietness of the area and/or to missing of data and the poor coverage for the local and
regional seismic stations. The spatial epicentral distribution in western desert shows
that there are two seismic zones (zone I and zone II), as shown in Figure (2.10 b).The
second one is more active than the first zone. Most events in zone (II) locate in and
around the Rutbah uplift, the outcropped tectonic feature in the studied area. It can
suggest that there is a causal association between the seismicity of western desert and
the buried intrusions and fault intersections. A better understanding of the seismicity of
western desert requires information about the distribution of stresses and strain within
area, geophysical surveys to better resolve crustal structure, heat flow data, detailed
microearthquakes monitoring and more detailed studies of the seismicity including
accurate hypocenter location and focal mechanisms.
08
(a) (b)
Figure (2.10) (a) Location Map of the Studied Area. (b) The Epicentral Distribution
of earthquakes with Mw ≥ 3 in Western Desert During 1900-2004 (after Al-Heety,
2010).
Abd-Alridha and Jasem (2013) studied the area bounded by latitudes 29° to
34° N and longitudes 39° to 48°E.The seismicity of area for the period 1980–2011 is
evaluated, as shown in Figure (2.11). In this study the geological and topography were
performed, regarding the historical seismicity. More than (145) events were re-
analyzed in Iraqi Seismological Network (ISN) and the recorded data was subjected to
statistical analysis.
Figure (2.11) Map of the study area (after Abd Alridha and Jasem, 2013).
09
This study shows high activity in the east and very low activity in the west. The
main conclusions that may be drawn from this paper were:
 The study area was subjected to more than (30) historical earthquakes of magnitude
range as (1.7-4.8), (3.1-5.3), (0.7-5.4), (2.3- 5.9), (1.8 – 4.8), for local Richter
magnitude.
 The temporal distribution for the recorded events of the study area, show the period
from (2009-2011) is the highest period of seismic activity followed by the period
from (1988- 1990) and the high seismicity periods: 1988, 2001, 2009, 2010 and
2011, are attributed to a tectonic cause rather than being attributed to a result of the
progress of earthquake monitoring in this region and surroundings in recent years.
Mohammed et. al. (2014) documented the earthquakes and their damages, to
collect data on the effect of four earthquakes that took place in the north of Mosul, to
determine the relation between their epicenters and the regional geology of the area and
to estimate the magnitude of the fourth shock that was not recorded in Mosul
seismological center as shown in Table (2.4).
On the 11th of March 2013, at 5:58 pm, Monday a shock was felt in Mosul city and its
surroundings to the northeast, north and northwest. The shock lasted for 5 seconds and
was registered in Mosul seismological center with magnitude of 4.9 degrees on Richter
scale. Two other shocks were recorded after few days. People in the villages located
north of Mosul have heard high roaring, which accompanied the shock the sound of
fallen large rock masses on a metallic plate. Many old buildings, among them the
church of Tell Asquf village was cracked and the plaster of the church's dome fell
down in fragments. Many other mud huts and some buildings showed severe cracks in
many other villages. No rupturing on the earth's surface was reported in the involved
areas. No live causalities and/ or wounded people were reported.
From the study, the followings were concluded:
• The epicenters of the first and second earthquakes were located along a reverse fault
that runs along the southwestern limb of Maqloub anticline.
• The first three earthquakes were felt in all investigated villages, as well as in Mosul
city.
11
• The first three earthquakes were of light type, whereas the fourth one was of minor
type; both on Richter and Mercalli scales, with magnitudes of 4.9, 4.5 and 4.5 degrees,
respectively, and with estimated magnitude of (3 – 3.5) degrees for the fourth one.
According to Mercalli scale, the first three earthquakes have intensity of IV – V,
whereas the fourth one is of estimated intensity of III – IV.
Table (2.4) Locations and magnitudes of the four earthquakes (after Mohammed et.
al., 2014).
* Estimated data from interviews.
2.4 Effect of Earthquake

Many researchers have investigated earthquake effects and concluded that
considering maximum ground acceleration only is not sufficient measure of potential
damage. There are other soil effects on the amount of damage to the buildings during
earthquake.
Earthquakes can give rise to ground rupture, slope instability, liquefaction,
cyclic softening, deformation, tectonic subsidence and liquefaction/lateral spreading
induced subsidence due to extensive liquefaction, and the potential for such effects to
occur, and their effect on the road and the associated structures, should be considered.
The damages due to earthquake can be classified into direct seismic effects and indirect
seismic effects ( Bridge Manual, 2013).
A. Direct effects
The direct seismic damages occurs due to,
- surface faulting.
- liquefaction.
- ground shaking.
- sliding of superstructure on its foundation.
- structural vibration
B. Indirect effects
Tsunamis, seiches, landslides, floods and fires are the indirect effects of
10
earthquakes. These may occur either alone or in combinations to add to

the damages during an earthquake.
Among earthquake effects, soil liquefaction has attracted considerable attention
from geotechnical engineering researchers over the past 35 years. As soil liquefaction
occurred when high porewater pressures are generated in a substantially thick soil layer
that is relatively near the ground surface, the upward flowing porewater may carry sand
particles up to the ground surface where they are deposited in a generally conical pile
called a sand boil. While sand boils represent the most common evidence of subsurface
soil liquefaction, they are not damaging by themselves. Liquefaction can, however,
produce significant soil deformations, both horizontal and vertical, that can cause
significant damage to a variety of structures (Kramer and Elgamal, 2001).
2.5 Soil-Structure Interaction

The response of a structure to earthquake shaking is affected by interactions
between three linked systems: the structure, the foundation, and the soil underlying and
surrounding the foundation (The Federal Emergency Management Agency FEMA,
2009). Soil-structure interaction analysis evaluates the collective response of these
systems to a specified ground motion. The terms Soil-Structure Interaction (SSI) and
Soil-Foundation-Structure Interaction (SFSI) are both used.
A seismic soil-structure interaction analysis evaluates the collective response of
the structure, the foundation, and the geologic media underlying and surrounding the
foundation, to a specified free-field ground motion. The term free-field refers to
motions that are not affected by structural vibrations or the scattering of waves at, and
around, the foundation (FEMA, 2009). SSI effects are categorized as inertial
interaction effects, kinematic interaction effects, and soil-foundation flexibility effects.
The terms kinematic and inertial interaction were introduced in 1975 by Robert
Whitman (Kausel, 2010).
Pile foundation response during earthquakes is strongly affected by nonlinear
soil-pile foundation interaction. The damages to pile foundations due to earthquake
were obviously attributed to nonlinear interaction of soil-pile foundation-superstructure
(Miyamoto, 2000). Seismic soil-pile-structure interaction is a complex phenomenon
that can affect the response of structures significantly during earthquake. Considering
complexities which exist in soil-pile-structure interaction problemsca, it is necessary to
11
use numerical methods for analyzing soil-pile-structure interaction problems (Ahmadi

and Ehsani, 2008).
George (1992) studied the effect of subgrade reaction on the behavior of
structures subjected to earthquake excitation. The earthquake time –acceleration
history of El-Centro earthquake has been taken as input data. The structure was
assumed linear elastic, and the foundation was assumed to be a rigid footing rested on
an elastic half space presented as springs of two degrees of freedom .The analysis is
carried out for different sets of steel frames, with varying span lengths, and number of
bays, with different soil rigidities.
Then, examined the effect of type of foundation for different types of structures.
It was found that the type of foundation has a great influence on the behavior of the
framed buildings, and that the rigidity of the soil strata affects that behavior. Finally a
comparison is made between the analytical values, and the values obtained from
various building codes.
Al-Damluji and Al-Ani (2005) analyzed Baghdad tower for communications
when subjected to earthquake excitation using an elasto-viscoplastic material modeling
and a three dimensional finite element method. The algorithm used in this research
deals with nonlinear structural analysis. Newmark's method is employed to study the
displacement response under (El-Centro , California, USA, May 1940) earthquake
excitation. The results showed that the maximum amplitude for displacement is 0.27m
and 0.16m, when it is subjected to the El-Centro excitation. Concluded that the Tower
is safe because the results are below the maximum permissible amplitude of vibration
as specified by Yugoslav Building Code.
2.6 Kinematic Bending Moment

According to the European Standard (Eurocode 8, 2004) and the Preliminary
draft of Iraqi Seismic Code, submitted to Central Organization for Standardization and
Quality Control COSQC (PISC, 2013), kinematic bending moment developed in piles
during earthquakes when seismic waves passing through the surrounding soil it become
significant when there are changes in the stiffness of soil profile , in this case large
curvature imposed into the pile by the vibrating soil in turn generate bending moments,
11
these bending moments generated even in the absence of superstructure and are known
as kinematic bending moments.
Margason and Holloway (1977) suggested a simplified approach to evaluate
the kinematic bending moment, they assumed that the soil layer is linearly elastic and
isotropic, and the pile behavior is same semi-infinite beam. The main assumption was
that the pile follows the free field soil motion. Under these conditions, the bending
moment at depth (z) can be computed by the following equation:
(2.8)
Where (1/R(z,t)) is the curvature of the vertical line of soil displacements with
depth, Ep and Ip are the pile elastic modulus and the pile moment of inertia,
respectively. The disadvantages of this approach are neglecting the interaction between
pile and soil and several important parameters such as the soil-pile relative stiffness,
pile slenderness, radiation damping, nonlinearity behavior of soil. This method is also
inapplicable to layered soil and inhomogeneous soils.
Dobry and O’Rourke (1983) developed the first formula for evaluation of the
kinematic bending moment at the interface between two layers of soil by modeling the
pile as Beam on Nonlinear Winkler Foundation BNWF. They assumed each layer of
the soil is homogenous and isotropic with the shear module G1 and G2 , Ep and Ip are
the pile elastic modulus and the pile moment of inertia, respectively. The shear strains
are calculated with γi =τ/Gi . The pile bending moment at the interface between two
layers:
( ) (2.9)
Where F is a function of the ratio c:
⁄ (2.10)
(2.11)
They used the equation of (Seed and Idriss, 1982) in determining the shear
strain at the upper layer (γ1 ):
(2.12)
⁄
11
Where amax,s is the maximum acceleration at surface based on seismic zonation;

H1 and ρ1 are the thickness and the density of the upper layer, respectively. rd= ( 1-
0.05z) is the depth factor; z is the depth from the ground surface (only z≤ 15 m). This
simplified method does not consider the nonlinear behavior of soil.
Nikolaou et. al. (2001) developed another simplified method based on the
Beam on Nonlinear Winkler Foundation BNWF model. The kinematic pile bending
moment is expressed by the following equation:
(2.13)
WhereVs1 and Vs2 are the shear wave velocity in the upper and lower layer,
respectively. τc is the maximum shear stress at the interface, Ep and Ip are the pile
elastic modulus and the pile moment of inertia, respectively.
Mylonakis (2001) presented the second simplified method after the Dobry and
O’Rourke formula . The assumptions are the same of the Dobry and O’Rourke model:
the soil profile is constituted by two layers of homogeneous linear elastic soils, both
layers are assumed to be thick. Both of the radiation and the hysteretic damping were
taken into account. The seismic excitation is a harmonic horizontal displacement
imposed at the bedrock. Base on his studies, the maximum bending moment expressed
as:
( )( ) ⁄
(2.14)
While r is the pile diameter; γ1 is the strain of the upper layer; Q is an

amplification factor so that its value is less than 1.25(usually Q is equal to 1). εp/γ1 is
the strict strain transfer function that can be computed by the following equation:
( )( ) [[ ( ) ( ) ] ] (2.15)
k1=δE1 (2.16)
(2.17)
Where G1 andG2 the shear module, Ep and Ip are the pile elastic modulus and the
pile moment of inertia, respectively. υ is the Poisson’s ratio; the free-field site analysis
is suggested for estimate the peak shear strain (γ1) by Mylonakis. In addition,
11
Mylonakis stated that the peak shear strain can be computed by (Seed and Idriss, 1982),
equation (2.12).The maximum shear stress at the interface (τc) is:
τc= amax,s ρ1 H1 (2.18)
This procedure does not consider the nonlinear behavior of the soil.
Maiorano et. al., (2009) evaluated kinematic bending moments in single piles
and pile groups , A quasi three-dimensional finite element program has been used to
perform dynamic analyses in the time domain. Piles have been considered as elastic
beams, while the soil has been modeled using a linear elastic constitutive model. In
Figure (2.12), the kinematic bending moments at the interface of the two layers
obtained from the FE analyses are compared with those evaluated through the
simplified methods (Dobry and O’Rourke ,1983, Nikolaou et al ,2001, Mylonakis
,2001 methods), for different values of the interface depth H1, the bending moments
obtained by the simplified expressions increase for increasing values of the interface
depth, whereas those computed by the finite element analyses exhibit a sort of
‘‘plateau’’, input seismic data type also affects the kinematic bending moment results.
Figure (2.12) Comparison between bending moments predicted by analytical

solutions and those evaluated by the finite element analyses for subsoils (Vs1 = 100
m/s) under the action of Tolmezzo (1976) and Norcia Umbra(1997) earthquakes
(after Maiorano et. al., 2009).
Dihoru et. al., (2010) applied a series of shaking table tests to study the
kinematic response of flexible piles in layered soil deposits under seismic excitation.
These tests were carried out in a deformable shear stack as shown in Plate (2.1), where
the dynamic responses of the pile and the free field were recorded for various seismic
inputs (earthquakes Friuli,1976(TMZ records) and Irpinia,1980(STU records)), soil
configurations and pile head boundary conditions. The pile bending moments were
measured along the length of the pile using strain gauges. The bending moment profiles
16
are compared with the predictions made by three theoretical models of kinematic soil-
pile interaction: (a) Dobry & O’Rourke (1983); (b) Mylonakis et al.(1997) and (c)
Nikolaou et al. (2001). This study showed that the theoretical models predicted the
maximum kinematic pile response with a variable degree of success as shown in Figure
(2.13). The observed differences can be attributed to the limitation imposed by the
idealizations in the respective model regarding the non-linear nature of the soil.
Plate(2.1) Shear stack installed on the earthquake simulator (after Dihor et.al.,
2010).
Figure (2.13) Experimental and theoretical results of maximum kinematic bending

moment at the interface in free head pile tests (STU=Sturno-A000, TMZ=Tomezzo-
A270) (after Dihoru et. al., 2010).
2.7 Piles behavior under earthquake action

Pile foundations have been the subject of interest for earthquake engineers since
last several decades. The devastations caused in major earthquakes of the world can be
the reason enough to carry out the research on the topic of seismic behavior of piles
(Mukhopadhyay et. al., 2008).
Many researchers around the world analyzed the behavior of soil pile system
using finite element method (FEM) and different computer programing methods.
17
Miyamoto Y. (2000) studied the pile foundation response during earthquakes

which is strongly affected by nonlinear soil-pile foundation interaction. The damages to
pile foundations during the Hyogo-ken Nanbu earthquake of 1995 were obviously
attributed to nonlinear interaction of soil-pile foundation-superstructure. Dynamic
centrifuge tests are performed on a four-pile group foundation model embedded in
saturated fine sand layers, as shown in Figure (2.14 a). The pile foundation model is
excited by a shaking table at the pile tip and by lateral loading at the pile head to
investigate the effect of inertia force and soil displacement, respectively, on pile
bending moments , as shown in Figure (2.14 b). The inertial and kinematic pile bending
moments are compared with analytical results concluded that pile bending moments
near the pile head are greatly affected by the inertial force of the structure, and the
inertial component reaches deeper in the pile under soil nonlinearity. The kinematic
component occurs due to the increase in soil displacement induced by liquefaction, and
extends from the pile tip to the pile head.
(a) (b)
Figure (2.14) (a) Centrifuge test model and measuring instruments. (b) Test cases
(after Miyamoto Y., 2000).
Ahmadi and Ehsani (2008) studied the effect of changing soil properties on
the lateral seismic behavior of pile. Shear forces, bending moments and deflections of
the pile due to variations in sand density, friction angle and Poisson's ratio were
predicted. The increment in both sand density and friction angle results in smaller
values for maximum bending moments and shear forces as shown in Figures (2.15) and
(2.16), while by increasing the sand density and friction angle, the pile deflection
remains nearly constant. Also in this study it is observed that sand Poisson's ratio
18
which does not have any considerable effect on pile forces and by increasing the sand
Poisson's ratio no significant change in the maximum bending moment, shear force and
deflection of the pile is predicted.
Figure (2.15) Maximum bending moments in the pile versus sand density (after
Figure (2.16) Maximum shear forces in the pile versus sand friction angle (after
Muthukkumaran and Subha (2010) studied the performance of piles in

liquefying ground under earthquake loading, liquefaction is a complex problem due to
the effects of a progressive build-up of pore water pressures in the saturated soils. The
loss of soil strength and stiffness due to liquefaction may develop large bending
moments and shear forces in piles, possibly leading to pile damage. They investigated
the effect of earthquake induced lateral soil movement on piles in sloping ground using
1995 Kobe earthquake data (Japan). Parametric study has been done on the same model
by varying slope in the soil layers and L/D ratio of the pile. The dynamic analysis was
carried out for slope angle of 1V:1.5H in with L/D=16, L/D=25 and L/D=33. In each
case, bending moment and displacement variation with depth of the pile is noticed.
19
Based on the study, it is concluded that for a constant slope and constant depth of
liquefiable layer, lateral displacement and bending moment is significantly increased at
L/D=16 when compared to higher L/D ratios of 25 and 33 as shown in Figure (2.17
a,b). However, further increase in L/D ratio is not having any significant effect in the
lateral displacement.
(a) (b)
Figure (2.17) (a) Depth of the pile vs bending moment. (b) Depth of the pile vs.
displacement (after Muthukkumaran and Subha, 2010).
Phanikanth et. al. (2011) analyzed soil-pile interaction model shown in Figure
(2.18 a) by considering stiffness degradation effects for a range of earthquakes with
different amplitudes [Maximum horizontal acceleration, (MHA)], frequency contents,
and different durations. Figure (2.18 b) shows the deflected shape of free headed pile in
liquefied soils considering various ground motions. The pile response is observed for
both rigid piles and flexible piles under earthquake loading. Effects of both kinematic
and inertial interactions are considered by using seismic deformation method. Results
of ground response analysis obtained from separate study were used for soil-pile
interaction analysis. Pile response for kinematic interactions is validated with the
available solutions in the literature. Parametric studies have been carried out to
understand the effect of depth of embedment, depth of liquefying layer etc. and their
results are presented. It is observed that the effect of depth of liquefying layer has
significant influence on the pile bending response. Also it is observed that the peak
bending moment occurs at the interface of liquefying and non-liquefying layer.
11
(a) (b)
Figure (2.18) (a) Pile passing through liquefied layer. (b) Pile deflections in
liquefied soils considering various ground motions –Free headed pile (after
Phanikanth et. al., 2011).
Ali (2014) investigated the response and examined the performance of piers
with the soil surrounding them under actual seismic loads recorded in middle and south
of Iraq during the last few years using (ANSYS 14.5) finite element program to check
whether these typical piers and surrounding soils can bear the stresses induced due to
earthquake loads. The finite element model included modeling of bridge substructures
and soil surrounding them with the actual dimensions and actual propertie
corresponding to "Sheikh Sa'ad Bridge" in Sheikh Sa'ad district at Wasit Governorate
37km south east of Kut city. The soil consists of sand as a lower strata and clay as a top
strata in presence of water table at 1.1m from natural ground level and the bridge pier
substructure consists of three bored piles with a pile cap, it was found that typical piers
used in bridges in Iraq can sustain earthquakes up to those with a magnitude of M L =
6.8 maximum.
Mokhtar et. al. (2014) investigated the pile instability due to liquefaction of loose
sand as one of the most important causes of bridge failures during earthquakes. The 3D
finite element program DIANA 9.3 is implemented to study the seismic behavior of
piles penetrated into liquefiable sandy soil. The model was supported by a special
Line–Solid Connection element to model the interface between pile and surrounding
soil. Extensive studies were performed to investigate the effects of soil submergence,
pile diameter, earthquake magnitude and duration on pile lateral deformation and
10
developed bending moment along pile shaft. They examined the three distinctive
failure mechanisims in piles subjected to lateral spreads resulting from soil liquefaction
modes which were proposed by Meyersohn (1994) as shown in Figure (2.19). In the
first one, when the pile reaching its bending capacity, thus developing a plastic hinge.
On the other hand, the lack of sufficient lateral support due to the reduced stiffness of
the liquefied soil and the lateral deflection imposed on the pile may result in buckling.
Another type of failure involves excessive rotation of the pile, which is a characteristic
of large diameter piles and piers. This type of response to lateral soil displacement
arises primarily from a lack of sufficient restraint at the bottom of the pile, either due to
an inadequate embedment length or due to low resistance of the foundation material
against lateral movement.
Study results showed that earthquake magnitude and time duration have a
particular effect on the pore water pressure generation and hence pile lateral
deformation and bending moments. The results also show the benefits of using
relatively large diameter piles to control the lateral displacement. It has been concluded
that the stress acting on pile is less than the Euler’s stress, so buckling failure will not
take place. Considering study results, it is concluded that designing the reinforced
concrete pile section to resist safely the exerted bending moments may cover the risk of
both buckling and plastic hinge mechanism. Recommendations are presented for
designers to perform comprehensive analysis and avoid buckling and plastic hinge
failures.
Figure (2.19) Pile failure mechanisms (after Meyersohn, 1994).
11
Hokmabadi et. al. (2014) studied the effects of the seismic soil-pile-structure
interaction (SSPSI) on the dynamic response of buildings with various heights by
conducting a series of shaking table tests on 5-, 10-story, and 15-story model structures
as shown in Figure (2.20). Two types of foundations for each case are investigated,
including (1) a fixed-base structure, representing the situation excluding the soil-
structure interaction; and (2) a structure supported by an end-bearing pile foundation in
soft soil.
Figure (2.20) (a) Prototype 15-story building supported by end-bearing pile

foundation; (b) prototype 10-story building supported by end-bearing pile
foundation; (c) prototype 5-story building supported by end-bearing pile foundation
(after Hokmabadi et. al., 2014).
An advanced laminar soil container has been designed that uses three-
dimensional numerical modeling to minimize the boundary effects and to simulate free-
field motion during the shaking table tests. Four real earthquake events, including Kobe
1995, Northridge 1994, El Centro 1940, and Hachinohe 1968, are imposed to each
model. According to the experimental measurements, it is observed that the SSPSI
amplifies the maximum lateral deflections and in turn inter story drifts of the structures
supported by end-bearing pile foundations in comparison with the fixed-base
structures.
11
2.8 Summary
The available previous studies investigated the behavior of piles under
earthquake action considering liquefaction of cohesionless soils or evaluating the
kinematic bending moment for piles.
Some Iraqi researchers studied the dynamic soil-structure interaction
behavior due to seismic activity considering acceleration-time data for earthquakes
of other countries rather than Iraq. Other Iraqi researchers simulate physical models
of piles and studied the behavior of piles under the action of vibrating machine.
In the present study, the real geophysical investigations data available for
different seismic active zones in Iraq will be collected to provide a database for the
dynamic parameters of soils used together with actual earthquake data from the Iraq
Seismological Network (ISN) records to simulate a typical model of soil-pile
system to be analyzed by PLAXIS 3D 2013 program.
11
CHAPTER THREE Database for Dynamic Soil Properties of Seismic Active Zones in Iraq
CHAPTER THREE
Database for Dynamic Soil Properties of Seismic Active Zones
in Iraq
3.1 Introduction
Design of geotechnical engineering problems that involve dynamic loading of
soils and soil–structure interaction systems requires the determination of three
important parameters, the shear modulus, Poisson's ratio and the damping of the soils.
The recent developments in the numerical analyses for the nonlinear dynamic
responses of grounds due to strong earthquake motions have increased the demand for
the dynamic soil properties corresponding to large strain level also. So it became
necessary to study the dynamic parameters of soils in different regions of Iraq. In this
chapter a data base is to be prepared for static and dynamic parameters of different soils
for seismic active zones in (North, Middle, Western south, Eastern south and South) of
Iraq. These parameters are evaluated from field and laboratory tests results of the
available geophysical and geotechnical investigation reports.
The latest Iraq seismic records would be collected from the Iraqi Seismological
Network (ISN) and prepared in terms of database. The soil parameters and seismic
records will be used in chapter five as input data for simulation of soil-pile interaction
model under earthquake excitation using PLAXIS 3D 2013 program.
3.2 Resource of Data and Presentation

The current study based on experimental results for underground conditions and
the engineering properties of the various strata of many geophysical and soil
investigation reports for projects in Iraq which is collected from engineering consulting
bureaus of Baghdad, Al-Nahrain and Technology universities, also from National
Center of Construction Laboratories and Research (NCCLR), and from other sources.
The available geophysical and soil investigation reports were for projects of
water treatment plants and pumping stations, multi-story buildings, electrical
substations, stadiums, oil refinery and other projects from different locations (North,
53
Middle, Western south, Eastern south and South) of Iraq as shown in Table (3.1) and
Figure (3.1).
Table (3.1) The available projects in some locations of Iraq with their site areas
and symbols.
No. Zone Site Project Site Symbol
1 Kirkuk Kirkuk North Gas Company 1 June Depot N1
North
2 Kirkuk Kirkuk Cement Factory N2

3 Kirkuk Kirkuk North Gas Company N3
4 Baghdad Al Karkh Pumping Station M1
5 Baghdad Al Zawra Stadium M2
Middle
6 Baghdad Eiwa'n Al Madain M3

7 Baghdad Al Taji Stadium M4
8 Baghdad Al Qudus Gas Turbine Power Plant M5
9 Babylon Hilla Power Plant M6
Eastern South Western South
10 Karbala Karbala Cultural WS1

11 Karbala Karbala Al Abbasia Sacred Shrine WS2
12 Al Najaf Al Najaf Al Salam Housing Complex WS3
13 Missan Al Amarah Water Intake Depot ES1

14 Missan Halfaya Oil Field ES2
15 Missan Missan Oil Export Pipe Line ES3
16 Al Dewaniya Al Dewaniya Pumping Station S1
17 Al Nasiriya Al Nasiriya Oil Depot S2
South
18 Al Nasiriya Al Nasiriya Water Intake Refinery S3

19 Al Basrah Faw Depot Turbine S4
20 Al Basrah Al Sheiba Oil Refinery S5
53
Figure (3.1) Seismic zones and projects locations in Iraq.
3.3 Geotechnical and Geophysical Parameters Investigated for Iraq Soils

The geotechnical and geophysical parameters for Iraq soils are collected from
different projects reports as mentioned before, the collection of data was performed
depending upon reports containing both soil investigation and geophysical
investigation data, borehole logs of each report are examined well so as the data of the
geotechnical and geophysical investigations for each project are collected either from
the same borehole or two adjacent ones which have the same soil layers profile.
53
For this study the basic input parameters for the Mohr-Coulomb model used in
PLAXIS 3D 2013 software program were investigated. The Mohr-Coulomb model
requires a total of five parameters, which are generally familiar to most geotechnical
engineers and which can be obtained from basic tests on soil samples. These
parameters with their standard units are listed below:
E : Young's modulus [kN/m2]
υ : Poisson's ratio [-]
ϕ : Friction angle [°]
c : Cohesion [kN/m2]
ψ : Dilatancy angle [°]
in addition to:
γsat : Saturated unit weight [kN/m3]
γunsat : Saturated unit weight [kN/m3]
Also the dynamic parameters which are used as input data in PLAXIS 3D 2013
program are:
Vs: Shear wave velocity [m/s]
Vp: Compression wave velocity [m/s]
Ed: Dynamic modulus of elasticity [kN/m2]
Gd: Dynamic shear modulus [kN/m2]
If there is some unavailable strength soil parameters (c or ϕ ) for particular

layers within the reports they would be either evaluated from N value (SPT) or
estimated according to type of soil. The database for the studied Iraq soils parameters
are shown in Table (3.2).
3.4 Soil Parameters Evaluation

Soil parameters such as; γwet ,γdry , c, ϕ are evaluated from field tests or
laboratory tests, other dynamic parameters such as; Vs and Vp are evaluated by
geophysical investigations in which other parameters like; E, G and υ are evaluated by
mathematical relationships mentioned in Section (2.2.2).
53
Table (3.2) Soil properties in different locations of Iraq.

No. Site Depth Soil Type WT γwet γdry c ϕ Vp Vs Ed 103 Gd 103 ν
(m) (kN/m ) (kN/m ) (kN/m ) (o) (m/s) (m/s) (kN/m ) (kN/m )
3 3 2 2 2
(m)
1. N1 Very stiff to hard
0-10 brown lean CLAY 3.8 20.1 17 130 0 1250 312 585.43 199.53 0.467
(CL)
2. N2 0-2.5 Stiff brown sandy
19 16.8 0 32 1125 225 290.15 98.09 0.479
SILT (ML)
2.5-15 Very stiff to hard
brown lean to fat 20.6 18.2 227 0 1250 321 634.86 216.38 0.467
>25
CLAY (CL,CH)
15-20 Very dense silty
GRAVEL with 20.6 18.2 0 42 2500 476 1409.8 475.98 0.481
SAND (GM)
3. N3 Stiff to very stiff
0-10 brown lean or fat 2.6 21.0 18.1 120 0 1541 304 585.82 197.91 0.48
CLAY (CL,CH)
4. M1 0-6 Medium stiff to
stiff brown fat 19.8 15.8 50 0 641 189 209.16 72.13 0.45
CLAY (CH)
6-12 Very stiff brown
19.0 14.5 100 0 675 248 338.44 119.17 0.42
lean CLAY (CL) 0.6
12-15 Medium dense to
dense silty clayey
19.0 15.0 0 37 750 225 284.46 98.09 0.45
SAND to silty
SAND with gravel
5. M2 0-7 Medium to hard
brown lean to fat 19.6 15.8 60 3 914 276 441.56 152.26 0.45
CLAY (CL,CH)
7-9 Very stiff grey
20.6 17.1 0 34 687 195 233.25 79.88 0.46
sandy SILT (ML) 2.3
9-14 Stiff to Hard brown
20.0 18.0 200 0 945 221 292.87 99.61 0.47
lean CLAY (CL)
14-15 Medium to dense
20.0 18.1 0 41 1014 327 628.09 218.09 0.44
grey silty SAND
6. M3 0-8.5 Medium to hard
brown lean to fat 20 16.3 35 0 454 161 151.00 52.8 0.428
CLAY (CL, CH)
8.5-11 Very stiff brown 3.9
19.6 17 200 0 625 232 305.41 107.54 0.42
SILT (ML)
11-12 Very stiff brown
19.6 17.2 240 0 1000 227 303.29 102.95 0.473
fat CLAY(CH)
7. M4 Stiff to very stiff
0-7.5 brown lean to
fat CLAY(CL- 19.8 17.1 65 10 841 165 162.7 54.97 0.48
CH) 2.2
Medium to very
7.5-12 dense grey silty 19.0 16.5 0 38 1025 279 440.3 150.8 0.46
SAND (SM)
53
Table (3.2) Continue.

3 3 2 o 2 2
(m) (m) (kN/m ) (kN/m ) (kN/m ) ( ) (m/s) (m/s) (kN/m ) (kN/m )
8. M5 Brown to grey clayey
silt to sandy silt with
0-1 filling materials, 19.00 15.8 28.7 0 322 140 105 37.96 0.383
organic to salts (ML)
Brown to Grey Silty
1.3
1-15 CLAY to Clayey Silt 18.88 14.7 31.5 0 776 219 268.9 92.34 0.456
(ML,CL,CH)
Grey Sand to silty or
15-20 clayey SAND to 22.31 17.04 0 38 1544 408 1107.4 378.73 0.462
Gravilly SAND
9. M6 Grayish sandy silty
0-2.4 CLAY soil, medium 16.18 14.5 144 0 306 111 57.9 20.33 0.424
consistency 1.5
Grayish silty sand
2.4-15 soil, medium dense 18.44 16.5 0 38 450 183 176.33 62.98 0.4
10. WS1 Dense white to
yellow slightly to
moderately gypseous
0-4.5 SAND with silt to 18.8 18 0 37 1433 284 457.0 154.6 0.478
silty SAND with
gravel (SP,SM)
Dense to very dense
white to yellow 0.8
4.5-12 SAND with silt 19.4 18 0 35 1733 550 1727.2 598.46 0.443
(SP,SM)
Very dense white to
yellow SAND with
12-22 silt to silty SAND 19.4 18 0 35 1650 563 1801 627.1 0.436
(SP,SM)
11. WS2 Stiff brown silty to
0-10.5 moderatly gypseous 18.5 14.7 100 0 1416 312 541.76 183.65 0.475
fat CLAY (CH)
Very loose to 1.5
10.5-14 medium green to
yellow marly SAND
19 17.1 0 50 1474 289 479 161.83 0.48
(SM)
12. WS3 Medium- dense light
brown slightly
0-1.2 gypseous silty SAND 19.1 17 0 43 805 268 458.15 159.3 0.438
(SM)
Medium- dense to
0.9 19.5
1.2-7 very dense light 18 0 40 1450 557 1743.5 616.95 0.413
brown SAND (SP)
Very dense light
7-10 brown silty SAND 19.6 18 0 39 1812 659 2472.2 868.03 0.424
(SM)
13. ES1 Medium stiff to stiff
0-7.6 brown lean to fat 19.5 15.1 80 0 500 176 175.96 61.57 0.429
CLAY (CL,CH)
7.6-9 Loose grey silty 0.6 19.5 15.7 0 29 600 200 228.51 79.51 0.437
SAND
Stiff brown lean
9-10 CLAY (CL) 19.5 15.7 60 8 600 250 346.6 124.23 0.395
04
Table (3.2) Continue.

3 3 2 o 2 2
(m) (m) (kN/m ) (kN/m ) (kN/m ) ( ) (m/s) (m/s) (kN/m ) (kN/m )
0-5 brown lean to fat 18.0 14.6 65 0 377 131 90.15 31.5 0.431
CLAY (CL,CH)
5-8 fat CLAY (CL,CH) 0.6
Stiff brown lean to
19.5 15.8 60 0 604 250 347.98 124.28 0.4
Stiff brown lean
8-17 CLAY (CL) 20.8 15.9 60 8 1362 420 1082.8 374.17 0.447
0-9 brown lean to fat 19.7 15.7 80 0 696 179 188.5 64.37 0.464
CLAY (CL,CH) 0.6
Stiff brown lean
9-18 CLAY (CL) 20.9 16.1 60 0 1167 380 886.78 307.76 0.44
16. S1 Brown lean
0-1.5 CLAY(CL)
18.5 14.4 94 0 625 188 193.28 66.65 0.450
loose grey silty
1.5-2 SAND layer (SM) 20.0 15.0 0 30 909 185 213.45 72.21 0.478
0.3
Medium stiff to very
stiff brown to green
2-10 marly lean to fat 19.3 14.7 60 5 909 200 232.17 78.73 0.475
CLAY (CL,CH)
17. S2 Very stiff brown lean
0-4 CLAY (CL) 19.07 15.1 34 0 600 200 223.45 77.75 0.437
Stiff to hard brown 4
4-10 lean to fat CLAY 19.93 15 112 0 750 240 337.6 117.1 0.442
(CL,CH)
18. S3 Soft to medium
black, brown, green
0-12 light, green lean to 19.5 15.2 90 3 434 110 70.54 24.06 0.466
fat CLAY (CL,CH)
Loose grey silty 1.7 20.8
12-14 SAND (SM) 18 0 41 500 145 129.7 44.6 0.454
Very stiff brown,
14-15 green lean 20.8 17 191 0 600 166 170.56 58.45 0.459
CLAY(CL)
19. S4 Very soft to very stiff
0-10 brown lean or fat 18.37 13.92 40 0 550 138 104.6 35.7 0.466
CLAY(CL,CH)
Grey silty SAND
10-13 (SM) 1.0 19.63 15.54 0 37 334 103 61.8 21.23 0.455
Very soft to very stiff
13-15 brown lean CLAY 20.02 16.03 48 0 450 102 62.57 21.24 0.473
(CL)
20. S5 0-3.7 Grey gypseous 18.18 - 5.33 39 566 230 244.6 87.29 0.401
SAND (SM)
1.8
Grey gypseous silty
3.7-15 SAND (SM) 19.16 - 8.4 40 1404 365 682.52 233.14 0.463
04
3.4.1 Field Testing
3.4.1.1 Standard Penetration Test (S.P.T)

The Standard Penetration Test, or SPT, is the most widely used in-situ test, in a
great variety of geotechnical exploration projects, in Iraq and throughout the world, as
an indicator of the density and compressibility of granular soils. It is also commonly
used to check the consistency of stiff or stony cohesive soils and weak rocks.
Estimation of the liquefaction potential of saturated granular soils for earthquake
design is often based on these tests. This test method provides a soil sample for
identification purposes and for laboratory tests appropriate for soil obtained from a
sampler that may produce large shear strain disturbance in the sample (ASTM D 1586
– 99).
Many published correlations which relate SPT blow count, or N-value, and the
engineering behavior of earthworks and foundations are available, Figure (3.2) shows a
useful relationship between N - values and shear wave velocities. Tables (3.3) and (3.4)
show the relationships between N-value and friction angle ϕ and unconfined
compressive strength qu, respectively. The test is performed using a barrel split spoon
sampler which is driven into the cased borehole by means of a 65 kg hammer falling
freely through a height of 760mm onto the top of the boring rods as shown in Figure
(3.3), different methods of releasing the hammer are used in different countries. The
borehole must be cleaned out to the required depth, care being taken to ensure that the
material to be tested is not disturbed. Initially the sampler is driven 150mm into the
sand to seat the device and to bypass any disturbed sand at the bottom of the borehole.
The number of blows required to drive the sampler a further 300mm is then recorded:
this number is called the standard penetration resistance (N). The number of blows
required for each 150mm of penetration (including the initial drive) should be recorded
separately. If 50 blows are reached before a penetration of 300 mm, no further blows
should be applied but the actual penetration should be recorded. At the conclusion of a
test the sampler is withdrawn and the sand extracted. Tests are normally carried out at
intervals of between 0.75 and 1.50m to a depth below foundation level at least equal to
the width (B) of the foundation, (Craig, 2004). The SPT has been used for many
04
purposes. At its simplest, it is a low quality sampler. At its most useful it is a rapid,
inexpensive, qualitative test which can provide data even when other techniques of
sampling or testing are not viable or cannot be justified financially. Due to the collected
reports the SPT was performed for each test boring at different intervals depending on
the stratification of the soil.
Figure (3.2) Relation Between Number of Blowes Per Foot in Standard

Penetration Test and Velocity of Shear Waves (after department of defense
handbook MIL-HDBK-1007/3, 1997).
Table (3.3) Correlations with N values of cohesionless soils (after Bowles, 1997).
Description Relative Density, Friction Angle, N Value
Dr (%) φ'(Deg.)
Very loose Less than 15 25 - 28 <4
Loose 15 - 60 29 - 32 4 - 10
Medium 60 - 75 33 - 35 10 - 30
Dense 75 - 90 36 - 40 30 - 50
Very dense Over 90 41 - 45 Over 50
05
Table (3.4) Correlations between unconfined compressive strength qu- N values

(after Terzaghi and Peck, 1967)
Consistancy N Value qu (kN/m2)
Very soft <2 <24
Soft 2-4 24-50
Medium 4-8 50-100
Stiff 8-15 100-200
Very stiff 15-30 200-400
Hard >30 >400
Figure (3.3) Standard Penetration Test (after Clayton, 1995).
3.4.1.2 Field density (Core Cutter Test)

This method provides the determination of bulk field density γwet of the surface
layers of soil or at the base of test pit; it is suitable for soft fine grained soils. A steel
cylinder (core cutter) is driven into the ground, dug out and the soil shaved off level.
The mass of soil is found by weighing and deducting the mass of the cylinder.
Determining the water content of small samples taken from both ends of the cylinder
(BS 1377:1999 part 9). Then the dry density γdry can be determined easily after
obtaining the water content w% of the soil.
00
3.4.2 Laboratory Testing

3.4.2.1 Soil Classification ( Sieve Analysis and Hydrometer )
According to (ASTM D 422-36) this test method covers the quantitative
determination of the distribution of particle sizes in soils. The distribution of particle
sizes larger than 75 µm (retained on the No. 200 sieve) is determined by sieving, while
the distribution of particle sizes smaller than 75 µm is determined by a sedimentation
process, using a hydrometer to secure the necessary data.
3.4.2.2 Direct Shear Test

This test method covers the determination of the consolidated drained shear
strength of a soil material in direct shear it is suitable for cohesionless soils. The test is
performed by inserting deformation to a specimen at a controlled strain rate on or near
a single shear plane determined by the configuration of the apparatus. Generally, three
or more specimens are tested, each under a different normal load, to determine the
effects upon shear resistance and displacement, and strength properties such as Mohr
strength envelopes (ASTM D 3080 / D3080M-98).
3.3.2.3 Unconfined Compression Test

This test method covers the determination of the unconfined compressive
strength of cohesive soil in the undisturbed, remolded, or compacted condition, using
strain-controlled application of the axial load. This test method provides an
approximate value of the strength of cohesive soils in terms of total stresses. This test
method is applicable only to cohesive materials which will not expel or bleed water
(water expelled from the soil due to deformation or compaction) during the loading
portion of the test and which will retain intrinsic strength after removal of confining
pressures, such as clays or cemented soils (ASTM D 2166-00).
3.4.2.4 Unconsolidated-Undrained Triaxial Compression Test (UU Test)

This test method covers determination of the strength and stress-strain
relationships of a cylindrical specimen of either undisturbed or remolded cohesive soil.
Specimens are subjected to a confining fluid pressure in a triaxial chamber. No
drainage of the specimen is permitted during the test. The specimen is sheared in
compression without drainage at a constant rate of axial deformation (strain
03
controlled). According to (ASTM D 2850-95) this test method provides data for
determining undrained strength properties and stress-strain relations for soils.
3.4.2.5 Consolidated Undrained Triaxial Compression Test (CU Test)

This test method covers the determination of strength and stress-strain
relationships of a cylindrical specimen of either an undisturbed or remolded saturated
cohesive soil. Specimens are isotropically consolidated and sheared in compression
without drainage at a constant rate of axial deformation (strain controlled). The
provided calculations are of total and effective stresses, and axial compression by
measurement of axial load, axial deformation, and pore-water pressure. This test
method provides data useful in determining strength and deformation properties of
cohesive soils such as Mohr strength envelopes and Young's modulus. According to
(ASTM D4767-04) three specimens are tested at different effective consolidation
stresses to define a strength envelope. The determination of strength envelopes and the
development of relationships to aid in interpreting and evaluating test results are
beyond the scope of this test method and must be performed by a qualified,
experienced professional.
3.4.2.6 Consolidated Drained Triaxial Compression Test (CD Test)

This test method covers the determination of strength and stress-strain
relationships of a cylindrical specimen of either intact or reconstituted soil. Specimens
are consolidated and sheared in compression with drainage at a constant rate of axial
deformation (strain controlled). This test method provides for the calculation of
principal stresses and axial compression by measurement of axial load, axial
deformation, and volumetric changes. This test method provides data useful in
determining strength and deformation properties such as Mohr strength envelopes.
According to ( ASTM D7181-11) three specimens are tested at different effective
consolidation stresses to define a strength envelope. If this test method is used on
cohesive soil, a test may take weeks to complete. The determination of strength
envelopes and the development of relationships to aid in interpreting and evaluating
test results are beyond the scope of this test method and must be performed by a
qualified, experienced professional.
03
3.4.3 Geophysical Investigation
3.4.3.1 Cross-hole Test

This technique consists of drilling two to three boreholes to depths below the
proposed foundation and requires the generation of elastic waves at certain depth down
a borehole. For this purpose SPT test hammer was used and the energy is transferred to
the base of the borehole by means of drill rods (Davis and Schultheiss, 1980). Vertical
shear and compressional waves propagating in a horizontal layer were detected by two
receivers placed in adjacent boreholes at the same depth as the energy source, as shown
in Figure (3.4). Galvanized pipes 7.5cm diameter were used for casing the boreholes.
The space between the pipe and borehole wall was filled by a soil material to make
firm contact between the Galvanized pipes and the borehole shaft.
The measurements were taken using a probe (consists of three geophones, two
horizontal, and one vertical), which get down on casing holes. The results of shear
wave velocity Vs and compressional wave velocity Vp were printed on seismic record
using (Terraloc ABEM) (ASTM D 4428/D 4428M – 00).
Figure (3.4) Cross hole test procedure (after Davis and Schultheiss 1980).
03
3.4.3.2 Down-hole Test

The basic seismic down- hole test consists of measuring the time of arrival of
wave from a source to a detector which occupies successive positions down a borehole,
as shown in Figure (3.5), a three component geophone lowered down and fixed against
the soil wall using a clamping device so that a good coupling could be made between
the instrument and the medium (Davis and Schultheiss, 1980). The source used for
generating elastic wave (compressional and shear waves) is placed at the surface some
distance from the hole and testing is carried out at 3m interval by striking a plate with
impact hammer . The detecting and recording equipment consists of three component
geophones (two are horizontal and one is vertical) (borehole picks) with a packer to fix
the probe at the required depth, coupled to the ABEM Teraloc seismograph which
record the results of shear wave velocity Vs and compressional wave velocity Vp
(ASTM D 7400–08).
Figure (3.5) Down hole test procedure (after Davis and Schultheiss 1980).
3.5 Rayleigh damping constants α and β

Material damping in dynamic calculations is caused by viscous properties of
soil , friction and development of irreversible strains. Damping is a function of
velocity, so if there is no motion then there will be no damping. According to PLAXIS
3D Manual (2013) all plasticity models can generate irreversible (plastic) strains, and
may thus cause material damping . Considering very small vibrations does not show
material damping , whereas real soil still show a bit of viscous damping . Hence,
03
additional damping is needed to model realistic damping characteristics of soils in

dynamic calculations. This can be done by means of Rayleigh damping.
Rayleigh damping is a numerical feature in which nxn symmetric damping
matrix [C] is formulated as a linear combination of the mass [M] and stiffness [K]
matrices:
[C]= α [M] + β [K] (3.1)
Where α is the mass-proportional coefficient and β is the stiffness-proportional

coefficient , alpha and beta are constants used to set the amount of damping. The type
of damping described by Equation (3.1) is known as Rayleigh or proportional damping.
This form of [C] is orthogonal with respect to the system eigenvectors. By applying the
modal coordinate transformation, the modal damping matrix [c] becomes diagonal:
[Ф]T[C][Ф]=[c]=α[1]+β[ω2] (3.2)
Rayleigh damping can be defined for linear and nonlinear dynamic studies.
Relation of Rayleigh Coefficients and Modal Damping Ratio The modal damping
matrix [c] is given by:
[c]=2[ζω] (3.3)
The coefficient of viscous damping ci for the ith. mode is calculated by:
ci=2ζiωi= α+βωi2 (3.4)
where ωi is obtained through modal analysis and ζi are damping ratios specified
by the user.
The damping ratio provides a mathematical means of expressing the level of
damping in a system relative to critical damping where ζi is expressed as (Lanzo, et.
al., 2003):
ζi= α / (2ωi) + βωi / 2 ζi (3.5)
If the damping ratios for the ith and jth modes are ζi and ζj, then the Rayleigh
coefficients α and β are calculated from the solution of the two algebraic equations:
03
⁄
{ } { } (3.6)
⁄
[ ]
If both modes have the same damping ratio ( ζi = ζj = ζ) , then the values of α
and β are given by:
(3.7)
β= ζ (3.8)
The damping parameters (α and β) can be automatically calculated by PLAXIS

3D 2013 program when the target damping ratio (ζ) and the target frequencies (f) are
specified . The viscous damping ratio ζ for any other mode varies with frequency as
shown in the Figure (3.6).
Figure (3.6) Variation of the viscous damping ratio ζ with frequency (after Lanzo
et. al. , 2003).
3.6 Earthquakes in Iraq

In the past, Iraq was considered as a low seismic active country but with the
increase of seismic action and the approach of seismic activity line coming from Iraq-
Iran boarders and Iraq-Turkey boarders the geodynamic configurations show a medium
to high seismic risk. This will be coupled with the increasing vulnerability of the major
highly populated cities. So it becomes important to study the earthquake events in Iraq
and their effect on dynamic behavior of soils and structures.
34
The latest seismic activities in Iraq are distinguished, the highest earthquakes
happened during the last five years at Ali Al-Gharbi in Missan are recorded by the
Iraqi Seismological Network (ISN) Badrah IBDR Station, as shown in Figure (3.7) .
1. Earthquake hit 20.72 km from Ali Al-Gharbi in Missan Province with ML = 4.9
magnitude at 18:42:58 local time on April 18, 2012, which was located at 32.462 lat.
and 46.902 long. Acceleration-time records are shown in Figure (3.8).
2. Earthquake hit 13.2 km from Ali Al-Gharbi in Missan Province with ML = 5
3. Earthquake hit 11 km from Ali Al-Gharbi in Missan Province with ML = 5
4. Earthquake hit 11 km from Ali Al-Gharbi in Missan Province with ML = 4.8
Figure (3.7) Location of the highest earthquakes hit Ali Al-Gharbi for the latest
five years recorded by the Iraqi Seismological Network (ISN), Badrah.
34
Figure (3.8) Earthquake reading hit 20.72 km from Ali-Al Gharbi recorded by the
34
Figure (3.10) Earthquake reading hit 11 km from Ali-Al Gharbi recorded by the
35
After classifying the four earthquakes according to their magnitude , intensity and
distance from Ali Al-Gharbi , as shown in Table (3.5), choosing the strongest
earthquake of Figure (3.10) to be applied on the model in this study.
Table (3.5) Classification of the distance ,magnitude and intensity of the four
earthquakes hit Ali Al-Gharbi during the latest five years.
Peak ground Peak ground
Figure acceleration velocity Instrument Perceived Potential
Region
No. (PGA) (PGV) Intensity Shaking Damage
(cm/sec2) (cm/sec)
20.72 km from Moderate Very Light
3-8 92.36394 7.00517 V-VI
Ali Al-Gharbi to Strong to Light
13.2 km from
3-9 49.05754 3.75036 V Moderate Very Light
Ali Al- Gharbi
11 km from
3-01 104.151 9.0036 VI Strong Light
Ali Al- Gharbi
12.38 km from Moderate Very Light
3-00 84.118 8.8293 V-VI
Ali-Al Gharbi to Strong to Light
3.6.1 Seismo Signal Program

In order to analyze and draw the readings of the strongest earthquake hits Ali
Al-Garbi on April 20,2012 as acceleration-time, velocity- time and displacement – time
graphs , Seismo Signal Program is used , as shown in Figure (3.12).
Acceleration [mm/sec2]
0.5
-0.5
-1
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600
Time [sec]
0.015
0.01
Velocity [cm/sec]
0.005
0
-0.005
-0.01
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600
Time [sec]
0.01
Displacement [cm]
0.005
-0.005
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600
Time [sec]
Figure (3.12) Seismogram of the strongest earthquake hit Ali Al-Gharbi.
30
SeismoSignal program is an easy and efficient way to process strong-motion data,

featuring a user-friendly visual interface and being capable of deriving a number of
strong-motion parameters often required by engineer seismologists and earthquake
engineers.
3.6.2 Seismic Zones in Iraq

According to Iraqi Seismic Code Requirements for Buildings (1997) .The
evaluation of seismic hazard in different seismic areas for the design of structures shall
be performed according to the seismic zoning map of Iraq, the seismic hazard zoning
coefficient are shown in Figure (3.13) which is used in design of structures.
Figure (3.13) Seismic Zone Map of Iraq (Iraqi Seismic Code Requirements for
Buildings, 1997).
33
3.6.3 Site Soil Seismic Classification

Site soil is classified according to PISC (2013) and FEMA (2010), as shown in
Tables (3.6) and (3.7) respectively ,while according to the European Standard
Eurocode 8 (2004), site soil is classified to type (A,B,C,D,E S1or S2) as shown in Table
(3.8), depending on one of the three methods:
1. Vs value method, the site soil should be classified according to the value of the
average shear wave velocity, Vs,30 , which represents a measurement or estimation
of average shear wave velocity in the upper 30 m of soil and could be computed in
accordance with the following expression:
(3.9)
∑
where H is the total depth of soil less than or equal to 30m, hi and vi denote the
thickness (in metres) and shear-wave velocity of the i-th formation or layer, in a
total of N, existing in the top 30 m.
2. N value method, another method used for site soil classification by N value of SPT
(Standard Penetration Test).
3. Su value method, using the undrained shear strength value Su or cu in the
classification of site soil.
Table (3.6): Site soil classification (after PISC, 2013 ).

Site Class Definition Vs N or Nch Su
A
Hard rock >1500 m/s - -
B
Rock 760 to 1500 m/s - -
C
Very dense soil or 370 to 760 m/s >50 >100kPa
soft rock
D
Hard soil 180 to 370 m/s 15 to 50 50 to 100 kPa
<180 m/s <15 <50kPa
E Each side section thickness greater than 3m for soil profile of the
Soft clayey soil following characteristics:
- Plasticity Index PI > 20.
- Water content w ≥ 40%.
- Undrained shear strength Su<25kPa
1. Soil exposed to possibility of collapse.
F
2. Silt and/or clayey soil of high organic content.
Soil types that require a
3. Clayey soil of very high plasticity index.
special field assessment
4. Very thick clayey soil of weak /medium strength.
33
Table (3.7) Site class and soil types (after FEMA, 2010).
General N
Site Class Vs Su
Description Blows/foot
>5000 ft/sec
A Hard rock - -
>1524 m/s
2500-5000 ft/sec
B Rock - -
762-1524 m/s
Very dense
1200-2500 ft/sec >2000 psf
C soil and >50
365-762 m/s >95kPa
soft rock
600-1200 ft/sec 1000-2000 psf
D Stiff soil 15 - 50
182-365 m/s 47-95 kPa
<600 ft/sec <1000 psf
E Soft clay soil <15
<182 m/s <47kPa
Unstable
F - - -
soils
Table (3.8) Ground Types classification (after Eurocode 8, 2004).

Parameters
Ground
Description of stratigraphic profile Vs,30 N, SPT cu
type
(m/ s) (blows/30cm) (kPa)
Rock or other rock-like geological formation
> 800
A including at most 5m of weaker material at - -
the surface.
Deposits of very dense sand, gravel, or very
stiff clay, at least several tens of metres in
360-800 > 250
B thickness, characterized by a gradual > 50
increase of mechanical properties with
depth.
Deep deposits of dense or medium- dense 70-
180-360
C sand, gravel or stiff clay with thickness from 15 - 50 250
several tens to many hundreds of metres.
Deposits of loose-to-medium cohesionless
soil (with or without some soft cohesive < 180 < 70
D layers), or of predominantly soft-to-firm
< l5
cohesive soil.
A soil profile consisting of a surface
alluvium layer with Vs values of type C or D
E and thickness varying between about 5 m
and 20 m, underlain by stiffer material with
Vs 800 m/s.
Deposits consisting, or containing a layer at
least 10m thick, of soft clays/silts with a < 100 10-20
S1 high plasticity index (PI> 40) and high water (indicative)
content
Deposits of liquefiable soils, of sensitive
S2 clays, or any other soil profile not included
in types A E or S1
33
3.6.4 Site Soil Seismic Classification of Iraq Soils

According to PISC (2013), FEMA (2010) and Eurocode 8 (2004), Iraq site soils
can be classified depending on the average shear velocity Vs as shown in Table (3.9).
The available geophysical investigations in Iraq provides Vs values for depths from 10
m to 22m.
Table (3.9) Iraq site soil classification.
Max. depth of PISC 2013
Vs Eurocode 8
No. Site Geophysical and
(m/s) 2004
Investigations (m) FEMA 2010
1 N1 10 312 D C
2 N2 20 330 D C
3 N3 10 304 D C
4 M1 15 217 D C
5 M2 15 245 D C
6 M3 12 177 E D
7 M4 12 190 D C
8 M5 20 240 D C
9 M6 16 198 D C
10 WS1 22 466 C B
11 WS2 14 306 D C
12 WS3 10 514 C B
13 ES1 10 185 D C
14 ES2 17 237 D C
15 ES3 18 243 D C
16 S1 10 198 D C
17 S2 10 222 D C
18 S3 15 116 E D
19 S4 15 124 E D
20 S5 15 319 D C
3.7 Conclusions from the collected database

The following conclusions from the collected database may be drawn:
1. The average vertical compressional and shear wave velocities, as well as, the
corresponding average dynamic moduli for soil layers, together with the soil
parameters γwet ,γdry , c, ϕ are evaluated. Thus, database of the soil and dynamic
parameters for seismic active zones in Iraq with earthquake data of Ali Al-Gharbi
33
are prepared to be used as input data for simulation of soil-pile interaction as

Mohr-Coulomb model under earthquake excitation using PLAXIS 3D 2013
program.
2. The average compressional wave velocities were ranged from (1125-2500) m/s in
the North, (306-1544) m/s in the Middle, (805-1812) m/s in the Western south ,
(377-1326) m/s in the Eastern south and (334-1404) m/s in the South of Iraq.
3. The average shear wave velocities were ranged from (225-476) m/s in the North,
(111-408) m/s in the Middle, (268-659) m/s in the Western south , (131-420)m/s in
the Eastern south and (102-365) m/s in the South of Iraq.
4. Modulus of Elasticity was ranged from ( 290.15-1409.8 ) MN/m2 in the North,
(57.9-1107.4) MN/m2 in the Middle, (457-2472.2) MN/m2 in the Western south ,
(90.15-1082.8) MN/m2 in the Eastern south and (61.8-682.52) MN/m2 in the South
of Iraq.
5. Shear modulus of elasticity was ranged from ( 98.09-475.98 ) MN/m2 in the North,
(20.33-378.73) MN/m2 in the Middle, (154.6-868.03) MN/m2 in the Western south
, (31.5-374.17) MN/m2 in the Eastern south and (21.23-233.14) MN/m2 in the
South of Iraq.
6. Seismic activity in Iraq was discussed and the strongest earthquake occurred in
Iraq for the latest five years was chosen to be used as an input dynamic excitation
for the model simulation in PLAXIS 3D 2013.
7. The studied Iraq site soils are classified according to different seismic codes
depending on Vs,30 value as shown in Table (3.9) , according to PISC (2013) and
FEMA (2010) the site soils are classified as types (E,D and C) while according to
Eurocode 8 (2004) site soils are classified as types (D, C and B) and concluding
that the studied Iraqi soils are ranging between;
a) Very dense soil , soft rock or gravel for WS1 and WS3 sites of the Western south
zone in Iraq.
b) Soft clayey soil or loose-to-medium cohesionless soil for M3 site of the Middle
zone in Iraq, also S3 and S4 sites of South zone in Iraq.
33
CHAPTER FOUR Finite Element Dynamic Modeling and Verification Problems
CHAPTER FOUR
Finite Element Dynamic Modeling and Verification Problems
4.1 General
Pile foundation under earthquake excitation is strongly affected by kinematic
and inertial interaction, the first represents soil - pile interaction and the later represents
pile - superstructure interaction. Dynamic analysis of soil- pile system is a complex
process and it cannot be solved explicit. Therefore numerical method will be used. The
finite element method is a very powerful tool for solving static and dynamic problems
of geotechnical engineering in which the domain is divided into sub domains called
elements connected with each other at selected points called nodes. In this study
PLAXIS 3D 2013 program had been used to simulate the soil and pile model.
In this chapter a finite element modeling of PLAXIS 3D 2013 program is
discussed and verification problems are examined.
4.2 Equations of Motion

The movement of piles and the surrounding soil under dynamic excitation can
be governed by an ordinary differential equation. The governing equation of motion is
derived for two types of dynamic excitation: external force and earthquake ground
motion (Chopra, 2011).
4.2.1 External Force

The dynamic analysis begins with a single-degree-of-freedom (SDOF) system.
Figure (4.1) shows the system of a single mass, supported by a spring and a dashpot, in
which the damping is of a viscous character. The spring and the damper form a
connection between the mass and an immovable base (i.e., the earth).
The equation of motion according to Newton’s second law when the force (P)
acts on the mass ( m ) causes the displacement of the mass (u).
m =P(t) (4.1)
60
Figure (4.1) Free Body Diagram of Single Degree of Freedom System (after
Chopra, 2011).
Assuming that the total force P consists of an external force F(t), and the
reaction of a spring and a damper. In its simplest form a spring leads to a force linearly
proportional to the displacement u, and a damper leads to a response linearly
proportional to the velocity du/dt. If the spring constant is k and the viscosity of the
damper is c, the forces acting upon the mass are (Lin and Chang, 2003):
1- Restoring force, FR: It is the force exerted by the spring on the mass and tends to
restore the mass to its original position. Restoring force is equal to:
{FR}=[K]{u} (4.2a)
where K is the spring constant and indicates the stiffness and u is the displacement.
This force always acts towards the equilibrium position of the system.
2- Damping force, FD: The damping force is considered directly proportional to the
velocity and given by:
{FD}=[C]{uʹ} (4.2b)
where C is called the coefficient of damping and uʹ is the relative velocity.
3- Inertia force, FI: It is due to the acceleration of the mass and is given by:
{FI}=[m]{uʹʹ} (4.2c)
where uʹʹ is the acceleration.
According to De-Alembert’s principle, a body which is not in static equilibrium
by virtue of some acceleration which it possess, can be brought to static equilibrium by
introducing on it an inertia force. This force acts through the center of gravity of the
body in the direction opposite to that of acceleration. The equilibrium of mass m gives:
P(t) = F(t) – C {u'} – K {u} (4.3)
[m]{uʹʹ} + [C]{uʹ} + [K]{u} = F(t) (4.4)
This is the equation of motion of the system shown in Figure (4.1) subjected to
external force F(t).
61
4.2.2 Earthquake Ground Motion

There is no external force applied directly on the foundation. Earthquake ground
motion generated at the rock layer and transmitted as waves through the soil to the
foundation , this excitation apply dynamic horizontal displacement to the foundation,
assume the displacement pile tip ug(t) , the pile cap undergoes horizontal displacement
relative to the pile tip u(t) , velocity u'(t) and acceleration u''(t). The total displacement
ut(t) is:
ut(t)= ug(t)+u (t) (4.5)
From the free-body diagram shown in Figure (4.2), the equation of dynamic
equilibrium is (Wagg and Neild, 2015):
FI+FD+FR=F(t) (4.6)
where:
FI: inertia force.
FD: damping force.
FR: restoring force.
Because the elastic and damping forces depend only on the relative
displacement and velocity not on the total quantities, Equations (4.2a) and (4.2b) still
apply. However, the mass in this case undergoes acceleration u'', and the inertia force
therefore is:
{FI}=[m]{u''t} (4.7)
Applying Equation (4.5) gives :
{FI}=[m]{u''g}+[m]{u''} (4.8)
Then the equation of motion to a pile subjected to earthquake acceleration ug''(t) is:
[m]{u''}+[C]{u'}+[K]{u}=-[m]{u''g} (4.9)
Comparison of Equations (4.4) and (4.9) shows that the equations of motion
for the structure subjected to two excitations; the first one is the ground acceleration =
u''(t) and the other is the external force –mug''(t) are one and the same. The deformation
response u(t) of the structure to ground acceleration will be identical to the response of
the structure on fixed base due to an external force equal to mass times the ground
acceleration, acting opposite to the sense of acceleration. The ground motion can
therefore be replaced by an effective force -mug''(t) .
62
Figure (4.2) Pile subjected to earthquake ground motion.
4.3 PLAXIS 3D 2013 Program

PLAXIS 3D 2013 is a three-dimensional program for geotechnical applications
in which soil models are used to simulate the soil behavior and developed for the
analysis of foundation constructions including raft foundations and offshore structures.
It is part of the PLAXIS product range, a suite of finite element programs that are used
worldwide for geotechnical engineering and design. The development of PLAXIS
began in 1987 at Delft University of Technology as an initiative of the Dutch Ministry
of Public Works and Water Management. PLAXIS was extended to cover most other
areas of geotechnical engineering. Because of continuously growing activities, the
PLAXIS company (PLAXIS bv) was formed in 1993. In 1998, the first PLAXIS 2D
deformation and stress analysis program for Windows was released. In the meantime a
calculation kernel for 3D finite element calculations was developed which resulted in
the release of the PLAXIS 3D TUNNEL program in 2001. 3D Foundation was the
second 3D PLAXIS program and was developed in corporation with TNO released in
2004. A new vision of 3D PLAXIS was released in 2010. The developed 3D PLAXIS
is a full three dimensional PLAXIS program which combines an easy to use interface
with full 3D modeling facilities. Dynamics is an add on PLAXIS 2D and 3D (PLAXIS
3D Manual, 2013). In this research PLAXIS 3D 2013 is to be used for modeling soil
layers, interfaces and piles under earthquake action. PLAXIS 3D 2013 consists of three
main parts which is Model, Calculation and Output mode (PLAXIS 3D Manual, 3013).
63
- Model mode
In the model mode, the geometry is built. Soil layer boundaries and material
properties are set. Construction element, such as piles , walls and beams are placed in
the model and interface properties are defined . Modeling loads static or dynamic loads.
Finally, the mesh is generated and refined to a proper level. The choice of soil model is
very important.
- Calculation mode
In the calculation mode, a number of calculation phases can be defined. Different
load cases and geometries are set to simulate a realistic building sequence. For every
step, different groundwater conditions can be set, and construction elements could be
activated. Excavation is simulated by deactivation of cluster. The calculation type must
be defined and could be plastic, consolidation or dynamic. The plastic calculation is
used to analyze the elastic-plastic deformations for drained or undrained soils.
Deformations and stresses are calculated for all nodes in serviceability limit state. The
result is depending on the choice of material model. Dynamic calculation is used to
calculate dynamic excitations such as earthquake records or harmonic excitation.
In the calculation mode there is an option to pre-select points of interest in the model. If
such a point is pre-selected, the displacement, the stress or the pore pressure of the
point for each iteration, step or time can be viewed in the sub program curves. The
results can be viewed in either a table or as a graphic curve.
- Output mode
The third main part of PLAXIS is the output mode and is used for post
processing of the calculation result. Deformations, strains, pore-pressures and dynamic
displacements are visualized for every phase of the calculation and for construction
elements bending moments and shear forces can be studied.
4.3.1 Drainage Type

Pore water pressure significantly affects the soil response, i.e. the relationship
between the stresses and strains associated with the soil skeleton. Several options
offered by PLAXIS 3D to enable incorporation of water-skeleton interaction in the soil
response. In Plastic calculation, Safety analysis and Dynamic analysis; the simplified
64
water-skeleton interaction is defined by drainage behavior. Different drainage types are

offered by PLAXIS 3D 2013:
 Drained behavior: when no excess pore pressures are generated, it is suitable for
describing the behavior of dry soils and also for full drainage of high permeability
soils.
 Undrained behavior: when pore water cannot freely flow through soil skeleton in
saturated soils. The undrained behavior in an effective stress analysis in PLAXIS
can be specified using effective model parameters. This is achieved by identifying
material behavior of a soil layer as Undrained (A) or Undrained (B) or Undrained
(C).
- Undrained (A) , an undrained effective stress analysis with effective stiffness

parameter. In this method the undrained shear strength (cu or su) is a consequence of
the model rather than an input parameter. Because most soil models are not capable
to provide the right effective stress path in undrained loading. This results in
producing the wrong undrained shear strength if the material strength has been on
the basis of effective strength parameters. Another reason that for undrained
materials, effective strength parameters are not provided by soil investigation data.
- Undrained (B), an undrained effective stress analysis with effective stiffness

parameter, it gives a prediction of pore pressure. In this method the undrained shear
strength (cu or su) is an input parameter and the friction angle ϕ is set to zero.
However when consolidation occurs, the undrained shear strength is not updated,
since it is an input parameter.
- Undrained (C), an undrained total stress analysis , it gives a prediction of pore

pressure . Therefore; it is not useful to perform a consolidation analysis In this
method the undrained shear strength (cu or su) is an input parameter and Poisson's
ratio value is close to 0.5 is selected (0.495-0.499). Undrained (C) method is
desired when Undrained (A) and Undrained (B) options are unsuitable in PLAXIS
3D 2013.
65
4.3.3 PLAXIS 3D 2013 Models

PLAXIS 3D 2013 can handle a number of soil models,
- Linear Elastic model (LE)
- Mohr-Coulomb model (MC)
- Hardening-Soil model (HS)
- Hardening Soil model with small-strain stiffness (HSsmall)
- Other special models in PLAXIS are Soft Soil Creep model (SSC), , Jointed
Rock model (JR), Modified Cam-Clay model (MCC), NGI-ADP model (NGI-
ADP), Sekiguchi-Ohta model and Hoek-Brown model(HB) .
4.3.3.1 Linear Elastic model (LE)

The Linear Elastic model is based on Hook's law of isotropic elasticity. It
involves two basic elastic parameters, i.e. Young's modulus E and Poisson's ratio υ .
Although this model is not suitable to model soil, it is used to model concrete walls,
footings, piles or intact rock formations.
4.3.3.2 Mohr- Coulomb Model (MC)

The elastic-plastic Mohr-Coulomb model involves five input parameters, i.e. E
and ν for soil elasticity; φ and c for soil plasticity and ψ as an angle of dilatancy are
defined previously in chapter three. Mohr-Coulomb model represents a 'first-order'
approximation of soil or rock behavior. This model is widely used for a first analysis of
the problem considered. The stiffness in Mohr-Coulomb model does not depends on
stress or stress-path or strain. In general , effective stress state at failure are quite well
described using the Mohr-Coulomb failure criterion with effective strength parameters
φ' and c'. For undrained materials , the Mohr-Coulomb model may be used with the
friction angle ϕ' set to 0o and the cohesion c set to cu (su) ,to enable the direct control of
undrained shear strength .
However, the Mohr-Coulomb model is simple and quick so it is the most
commonly used for most geotechnical engineering simulation models and also the
model used in most of the simulations in this study. The model is a linear elastic,
perfectly-plastic model, meaning that the material is behaving ideal elastic until all the
66
shear strength have been mobilized. When the yield criterion is reached, all load
increments will lead to plastic strains.
The basic principle of elastoplasticity is that strains and strain rates are
decomposed into an elastic part and a plastic part (PLAXIS 3D Manual, 2013) as
shown in Figure (4.3):
ε= ε e+ ε p (4.10)
Figure (4.3) Basic idea of an elastic perfectly plastic model (after PLAXIS 3D
Manual, 2013).
4.3.3.2.1 Formulation of Mohr-Coulomb Model

The Mohr-Coulomb yield condition is an extension of Coulomb's friction law to
general states of stress. In fact, this condition ensures that Coulomb's friction law is
obeyed in any plane within a material element.
τf = c + σ . tanφ (4.11)
Where τf defines the shear stress failure envelope, c is the cohesion and φ is the
friction angle, see Figure (4.4).
The soil stress, according to Mohr- Coulomb´s model, is related to the difference
between σ1 and σ3, which represent the major and the minor principle stress
respectively.
The Mohr-Coulomb´s failure envelope indicates that stress points under the line
are in an elastic state. When the stress circles touch the failure line, failure will occur,
i.e. the soil goes from elastic to plastic state.
67
The full Mohr-Coulomb (taking the third dimension into account), yield
condition represents the fixed hexagonal cone failure surface in principal stress space
of Mohr Coulomb's model. See Fig (4.5).
Figure (4.4) Mohr- Coulomb´s criteria of failure in two dimensions (after

Brinkgreve et al, 2013).
Figure (4.5) The failure surface of Mohr-Coulomb's model in principal stress space
for cohesionless soil (after Brinkgreve et al, 2013).
Inside this surface elastic deformations are developed depending Young´s

modulus, E and Poisson´s ratio, υ . When an element of the soil has reached the stress
surface, the elastic deformations goes to elastic-plastic deformations .
The plastic potential functions contain a third plasticity parameter, the dilatancy
angle ψ besides c and φ. The model described as the linear elastic perfectly plastic
model with Mohr-Coloumb failure criterion .
68
4.3.3.3 Hardening Soil model with small-strain stiffness (HS small)

The Hardening-Soil model is an advanced model for the simulation of soil
behavior. In this model soil stiffness is described much more accurately than Mohr-
Coulomb model by using three different input stiffnesses: the triaxial loading stiffness,
E50, the triaxial unloading stiffness, Eur, and the oedometer loading stiffness, Eoed. As
average values for various soil types, we have Eur ≈ 4 E50 and Eoed ≈ E50, but both very
soft and very stiff soils tend to give other ratios of E oed / E50. In contrast to the Mohr-
Coulomb model, the Hardening-Soil model also accounts for stress-dependency of
stiffness moduli. This means that all stiffnesses increase with pressure. Hence, all three
input stiffnesses relate to a reference stress, usually taken as 100 kPa (1 bar).
Hardening Soil model with small-strain stiffness (HS small) is a modified
method of the hardening soil model that accounts for the increased stiffness of soils at
small strains. Soils exhibit a higher stiffness at low strain levels than at engineering
strain levels, and this stiffness varies non-linearly with strain. This behavior is
described using an additional strain-history parameter and additional material
parameters, i.e. G0ref is the small-strain shear modulus and γ0.7 is the strain level at
which the shear modulus has reduced to about 70% of the small-strain shear modulus.
The advantage of this model over HS model that it gives more reliable displacements.
The Hardening Soil model with small-strain stiffness introduces hysteretic damping
when used in dynamic applications.
4.3.4 Soil Elements

The basic soil elements of the 3D finite element mesh are the 10-node
tetrahedral elements. The interpolation functions, their derivatives and numerical
integration of the element are described in the following subsections (PLAXIS 3D
Manual, 2013).
4.3.4.1 10-Node Tetrahedral Element

The 10-node tetrahedral element of the 3D mesh procedure provides a second-
order interpolation of displacements. For tetrahedral elements shown in Figure (4.6)
there are three local coordinates (ξ, η and ζ). The shape function Ni has the property
69
that the function value is equal to unity at node i and zero at other nodes. The shape
function can be written as:
N1 = (1 − ξ − η − ζ) (1 − 2ξ − 2η − 2ζ) (4.12)
N2 = ζ(2ζ − 1)
N3 = ξ(2ξ − 1)
N4 = η(2η − 1)
N5 = 4ζ(1 − ξ − η − ζ)
N6 = 4ξζ
N7 = 4ξ(1 − ξ − η − ζ)
N8 = 4η(1 − ξ − η − ζ)
N9 = 4ηζ
N10 = 4ξη
The soil elements have three degrees of freedom per node: ux , uy and uz . The
shape function matrix Ni can be defined as:
Ni = [ ] (4.13)
Then the nodal displacement vector v is defined as:
v = [vix viy viz] T (4.14)
Figure (4.6) Local numbering and positioning of nodes (•) and integration points
(x) of a 10-node tetrahedral element (after Brinkgreve et al, 2013).
70
Table (4.1) 4-point Gaussian integration for 10-node tetrahedral element (after
PLAXIS 3D Manual, 2013).
Point ξi ηi ζi wi
1 1/4-1/20√5 1/4-1/20√5 1/4-1/20√5 1/24
2 1/4-1/20√5 1/4-1/20√5 1/4+3/20√5 1/24
3 1/4+3/20√5 1/4-1/20√5 1/4-1/20√5 1/24
4 1/4-1/20√5 1/4+3/20√5 1/4-1/20√5 1/24
4.3.5 Embedded Pile Element

The embedded pile in PLAXIS 3D 2013 represents the interaction of a pile with
its surrounding soil. The interaction of the pile skin and pile foot are described by
means of embedded interface elements.
The pile is considered as a beam which can cross a 10- node tetrahedral element
at any place with any arbitrarly orientation (Figure 4.7), the beam element is a 3-node
line element which is compatible to the side of a 10-node volume element in the
PLAXIS 3D 2013 program, since this element also has three nodes on a side. The
shape functions Ni have the property that the function value is equal to unity at node i
and zero at the other nodes. For 3-node line elements, where nodes 1,2 and 3 are
located at ξ = -1, 0 and 1 respectively as shown in Figure (4.8), the shape function are
given by:
N1 = - 1/2(1 − ξ ) ξ (4.15)
N2 = (1 + ξ )(1 − ξ )
N3 = 1/2(1 + ξ ) ξ
Figure (4.7) Illistration of the embedded beam element denoted by the solid line ,
the blank grey circles denote the virtual nodes of the soil element (after PLAXIS 3D
Manual, 2013).
71
Figure (4.8) Shape function for a 3-node line element (after PLAXIS 3D Manual,
2013).
The 3-node beam elements are slightly different from 3-node line elements in the
fact that they have six degrees of freedom per node instead of three in the global
coordinate system , three displacement degrees of freedom ( ux , uy ,uz ) and three
rotational degrees of freedom (φ x , φ y , φ z ). The axial displacement can be defined as:
u*x=Ni v*ix (4.16)
where v*ix denotes the nodal displacement in axial direction of node i .

Assuming the displacement of soil us and the displacement of the pile up can be
discretized as:
us = Ns vs (4.17)
up = Np vp (4.18)
where Ns and Np are the matrices containing the interpolation function of the soil
elements and the beam elements respectively, vs and vp are the nodal displacement
vectors of the soil elements and the beam elements respectively.
4.4 Model Verification

The aim of the following sections is to verify the adopted nonlinear finite
element model by comparing with available studies. In order to check the validity and
accuracy of PLAXIS 3D 2013 Finite Element model for studying the behavior of pile
under seismic excitation, two dynamic models were examined. These models are of
different types for structures under different dynamic excitations with different
parameters and boundary conditions.
4.5 Study of Kinematic Bending Monent of Pile under Seismic Motion

Khari, et. al., (2014) developed a 2D Finite Element model to evaluate the
kinematic bending moment of a single pile at interface of two layer soil model under
72
seismic excitations (Figure, 4.9a). The results of this simulation were used to verify the
results of simplified approaches. The simplified approaches are existing design
methods for evaluating the kinematic interaction between soil-pile subjected to the
seismic excitations developed by Dobry and O’Rourke (1983), Mylonakis(2001) and
Nikolaou et al.(2001) ,the description of these approaches were explained in chapter
two (section, 2.6).
4.5.1 Overview and Model Information
The kinematic bending moment of a 2D FE model is evaluated using 2D
PLAXIS code. The overall dimensions of the model boundaries included a width of
11D (D=pile diameter) and a height equal to the thickness of the two subsoil layers as
shown in Figure (4.9, a). The model was meshed by 15-node wedge elements. While,
the horizontal outer boundary mesh of the model was fixed against displacements (ux,
uy) but the vertical outer boundary, only, was fixed in the horizontal displacement (uy).
Figure (4.9, b) shows the outer boundaries, absorbent boundary conditions were used to
absorb outing waves. The surrounding soil was considered as Mohr-Coulomb model
and the single pile was considered as linear-elastic material model. The soil-pile
interaction was modeled by the interface element. Kinematic interaction have been
performed for a single pile with a length L=20 (m); Young’s modulus Ep =
2.5x107(kN/m2); pile diameter D=60 (cm); mass density ρp=2.5(Mg/m3) and Poisson’s
ratio ν=0.15.
Figure (4.9, a) shows the pile is embedded in ideal two-layered subsoil. The
thickness of the second layer is assumed H2= 15(m) while the thickness of the upper
layer H1 is variable (5,10,12,15 and 18 m). The shear wave velocity of the upper layer
Vs1 is taken as 100 m/s, while Vs2 is assumed equal to two times Vs1. Also, the mass
density and Poisson’s ratio of the soil are: ρs= 1.97(Mg/m3) and ν=0.4, respectively.
The Young’s modulus can be computed based on the shear modulus (E=2G(1+ν)). In
addition, the undrained shear strength was calculated based on the ratio suggested by
the Applied Technology Council (ATC) (Gmax/Su=1000). The average shear wave
velocity can be computed by Equation (3.9). According to Eurocode 8 (2004), the soil
profiles can be classified as type D and C. Acceleration time history selected is scaled
73
to the peak ground acceleration of 0.1(g). Figure (4.10) shows the acceleration time
history and spectral acceleration selected at the bedrock roof (Khari, et. al., 2014) .
Figure (4.9) Reference scheme model (a) Soil model, (b) Typical 2D model for FE
Analysis (after Khari, et. al., 2014).
Figure (4.10) Acceleration time history and response spectra at the bedrock roof
(after Khari, et. al., 2014).
4.5.2 Finite Element Modeling of Problem using PLAXIS 3D 2013

Kinematic bending moments at interface of a pile embedded in two-layered soil
is evaluated using PLAXIS 3D 2013 software. Five models are simulated for the five
depths of the upper layer of soil (H1=5,10,12,15,18 m). The description of the modeling
and results of analysis will be explained in the following subsections.
74
4.5.2.1 Dimensions and Boundary Conditions of the Model

The overall dimensions of the model shown in Figure (4.11,a) are performed by
assuming X= Y=11D = 6.6(m) (D= diameter of pile) as a 3D model Z is variable (Z=
H1+H2). Using the default boundary conditions of PLAXIS 3D 2013 in which the
vertical boundaries (parallel to yz plane are fixed in x direction ux=0), (parallel to xz
plane are fixed in y direction uy=0) both are free in z direction, the bottom boundary is
fixed in all directions (representing the bedrock roof), while the ground surface is free
in all directions.
The absorbent boundary conditions of outing waves are performed by making
Boundary Xmax,min and Ymax,min viscous that waves are absorbed by the surrounding
soils , Boundary Zmax,min are None for unabsorbing bedrock roof.
(a) (b)
Figure (4.11) (a) 3D Soil profile model. (b) embedded pile model and earthquake
prescribed displacement at bedrock of the model using PLAXIS 3D 2013.
4.5.2.2 Soil and Interface Modeling

Soil layers are modeled by entering depths and material properties of both layers
according to Table (4.2), water table at the ground level. As in the verifying study
choose the model and drainage type as Mohr Coulomb and Undrained B, respectively.
Damping ratio is assumed to be equal to 5% according to (PLAXIS 3D Manual, 2013),
(Eurocode 8, 2004) and (PISC, 2013).
75
Table (4.2) Input soil parameters.

Parameter Name Soil 1 Soil 2 Units
Material model Model Mohr-Coloumb Mohr-Coloumb -
Drainage type Type Undrained B Undrained B -
Unit weight γsat , γunsat 19.32 19.32 kN/m3
Young's modulus E 55160 220.64 103 kN/m2
Poisson's ratio υ 0.4 0.4
Shear modulus G 19.7 10 3
78.8 103 kN/m2
Undrained shear strength Su 19.7 78.8 kN/m2
ο
Angle of internal friction φ 0 0
Shear wave velocity Vs 100 200 m/s
Damping ratio ξ 5 5 %
Interface strength - Rigid Rigid -
For Vs1=100m/s and Vs2=200m/s, using Equation (3.9) to calculate Vs,30 .

According to Eurocode 8 (2004) see Table (3.5) in chapter three, the soil profiles can
be classified as ground type shown in Table (4.3).
Table (4.3) Ground type according to (Eurocode 8, 2004).

H1 H2 Vs,30 Ground Type
5 15 160 D
10 15 143 D
12 15 138 D
15 15 133 D
18 15 129 D
4.5.2.3 Pile Modeling

Pile is modeled by its dimensions (Dp=0.6m) ,(Lp=20m) and material properties
(Ep=2.5x107 kN/m2), (γp=24.525 kN/m3), (υ=0.15). The embedded pile model is shown
in Figure (4.11).
4.5.2.4 Earthquake Modeling

Earthquake is modeled as dynamic prescribed displacement in the x-direction at
the bedrock level as shown in Figure (4.11, b), the readings of the earthquake are
entered as a table of time acceleration records in (s) and (m/s2), respectively.
Acceleration-Time records of earthquake shown in Figure (4.12).
76
Figure (4.12) : Earthquake acceleration-time records.
4.5.2.5 Mesh Generation

Unlike the 15-node triangular element of 2D PLAXIS, the 3D PLAXIS Finite
Element mesh consist of 10-node tetrahedral element shown in Figure (4.6). Mesh is
generated as in Figure (4.13).
Figure (4.13) Mesh generation of 3D model.
4.5.2.6 Performing Calculations

Calculations are performed through dividing the calculation process in to multi
Phases.
77
- Initial Phase is generated to calculate in Soils and Interfaces.

- Second phase generated to calculate Pile stresses using plastic calculation method.
- Third phase generated as a dynamic calculation method to calculate earthquake
stresses, the dynamic time interval is set to 20(s).
4.5.2.7 Analysis Results

The finite element analyses of the five models are set up to determine the
kinematic bending moments at pile interface due to earthquake excitation. Remodeling
the present study into 2D shape by reducing the Y dimension, the 2D dimensions
(X=6.6m and Y=1m) as shown in Figure (4.14). Figure (4.15) shows the kinematic
bending moment at the interface of the two layered subsoil , the results show that
moments are increased with increasing first layer thickness. The 3D model results are
higher than 2D calculated by Khari et. al. (2014) results specially at H1/H2=0.67,0.8,1
and 1.2 this occurs due to the effect of 3D modeling. The results of assuming 2D of
present study is too close to 2D of Khari et. al., (2014).
Figure (4.14) Model of 2D present study by PLAXIS 3D 2013.
Kinematic bending moments at the interface of the two layers were calculated
using the simplified approaches developed by Dobry and O’Rourke (1983), Mylonakis
(2001), and Nikolaou et al. (2001), were described in section (2.6). Then the simplified
approaches are compared with the moments of PLAXIS 3D model as shown in Figure
(4.15). The 3D PLAXIS moments are close to Dobry and O’Rourke (1983) moments
78
particularly at H1/H2=0.33 and 1.2. The PLAXIS 3D curve is similar in behavior to

Nikolaou et al.(2001) curve with lower values of moments.
100
80 Dobry and O’Rourke (1983)

Nikolaou et. al. (2001)
60 Mylonakis (2001)
M (kN.m)
Khari et. al. 2014

40 3D Present Study
2D Present Study
20
0
0 0.5 1 1.5
H1/H2
Figure (4.15) Comparison between PLAXIS 3D results of present study and results
of 2D Khari et. al., (2014) and simplified approaches' results.
The results of the dynamic analysis of the kinematic bending moments of the
single pile using PLAXIS 3D 2013 program are compared with Khari et. al., (2014) 2D
PLAXIS model and the simplified approaches in the two layers subsoil. The following
conclusions may be drawn:
1- The nonlinear behavior of soil under earthquake excitation wasn't cosidered in all
the mentioned simplified approaches. In Dobry and O’Rourke (1983) and
Mylonakis (2001) approaches, it is assumed that the seismic excitation as a
harmonic horizontal displacement imposed at the bedrock using the variable amax,s of
Equation (2.12). Nikolaou et al. (2001) consider Vs1 and Vs2 as dynamic variables of
Equation (2.13),while in PLAXIS 3D 2013 the acceleration–time history data was
entered as a prescribed displacement at the bedrock of the model in addition to
dynamic parameters of soil including wave velocities. It is concluded that the
kinematic bending moment values are affected by the method of analysis used.
2- As the first layer depth increased the kinematic bending moment at the interface of
the two layers increased to reach the maximum amount at H1/H2=1. The kinematic
pile moments during earthquake shaking occurs at relatively deep interfaces
between soil layers with very different stiffnesses.
79
3- The kinematic bending moment at the interface of the two layers decreased at
H1/H2=1.2, this is may be due to increasing the distance between the pile tip and the
source of excitation and 90% of pile length embedded in the first layer with Vs1<Vs2.
4- The evaluated ground type in Table (4.3), type D.
5- After comparing the results of PLAXIS 3D and the assumed 2D models of the
present study with the results calculated by (Khari et. al., 2014) then finding out that
the increased moment values at H1/H2=0.67,0.8,1 and 1.2occurs due to the effect of
3D modeling which represents the reality and should be analyzed as such.
6- The results of the study show that the kinematic bending moment at the interface is
affected by the soil nonlinearity behavior, thickness of soil layers and the frequency
content of the seismic motion even in absence of superstructure.
4.6 Free Vibration and Earthquake Analysis of A Building

In order to verify the efficiency of Mohr Coulomb model for simulating soil
model using PLAXIS 3D 2013, a model of a long five-story building under earthquake
excitation of Tutorial 8 (PLAXIS 3D Manual, 2013) is simulated using Hardening soil
model with small-strain stiffness (HSsmall) then re-simulate the same model using
Mohr Coulomb soil model (MC) with and without damping then comparing results.
Tutorial 8 , PLAXIS 3D Manual, 2013, The natural frequency of a long five-

story building when subjected to free vibration and earthquake loading was
demonstrated. A building consists of 5 floors and a basement. It is constructed on a
clay layer of 15 m depth underlayed by a 25 m sand layer. The model is simulated
using HS small material model.
4.6.1Geometry Model
The model dimensions are: X=160 m, Y= 3 m and Ztotal=55 m as shown in
Figure (4.16).
80
Figure( 4.16) Geometry of the model (after PLAXIS 3D Manual, 2013).
4.6.2 Soil Model

The subsoil consists of two soil layers, the upper clayey layer and the lower sandy
layer, water table at 15 m under ground level . The material models used are HS small
and MC , the drainage type is Drained, soils properties and model parameters are
shown in Tables (4.4) and (4.5) for both HS small model and Mohr -Coulomb model ,
respectively.
Table (4.4) Model parameters and soil properties of HS small model (after PLAXIS
3D Manual, 2013).
Parameter Name Upper clayey Lower sandy
layer layer Unit
General
Material model Model HS small HS small -
Drainage type Type Drained Drained -
Soil unit weight above phreatic level γunsat 16 20 kN/m3
Soil unit weight under phreatic level γsat 20 20 kN/m3
Parameters
Secant stiffness in standard drained
triaxial test
E50 ref 2.0 104 3.0 104 kN/m2
Tangent stiffness of primary
oedometer loading
Eoed ref 2.561 104 3.601 104 kN/m2
Unloading / reloading stiffness Eur ref 9.484 104 1.108 105 kN/m2
Power of stress level dependency of
stiffness
m 0.5 0.5 -
Cohesion c'ref 10 5 kN/m2
o
Friction angle φ' 18 28
o
Dilatancy angle ψ 0 0
Shear strain at which Gs=0.722G0 γ0.7 1.2 10-4 1.5 10-4
Shear Modulus at very small strains G 96.04 102 13.5 103 kN/m2
Poisson's ratio υ'ur 0.2 0.2 -
81
Table (4.5) Model parameters and soil properties of Mohr –Coulomb model
Upper clayey Lower sandy
Parameter Name
layer layer Unit
General
Material model Model Mohr-Coulomb Mohr-Coulomb -
Drainage type Type Drained Drained -
Soil unit weight above phreatic kN/m3
level γunsat 16 20
Soil unit weight under phreatic kN/m3
level γsat 20 20
Parameters
Effective Modulus of Elasticity E' 23.05 103 32.41 103 kN/m2
Poisson's ratio υ' 0.2 0.2 -
Shear Modulus of Elasticity G 96.04 102 13.5 103 kN/m2
Oedometer Modulus Eoed 25.61 103 36.01 103 kN/m2
Cohesion c' 10 5 kN/m2
Friction angle φ' 18 28 o
o
Dilatancy angle ψ 0 0
%
Without damping ξ 0 0
%
With damping ξ 5 5
4.6.2 Structural Model

The model of the building consists of 5 floors and a basement. Total dimensions
of the building is 10 m wide and 17 m high including the basement. The total height of
the ground level is 5 3 m=15 m and basement is 2 m deep . A value of 5 kN/m2 is
taken as the weight of the floors and the walls. Basement , floor and walls are modeled
as plates . The material dataset for the plates representing the structure are defined
according to Table (4.6).
Table (4.6) Structural plates properties (after PLAXIS 3D Manual, 2013).
Parameter Name Rest of Basement Unit
building
Thickness d 0.3 0.3 m
Material weight γ 33.33 50 kN/m3
Material behaviour - Linear; Isotropic Linear; Isotropic -
Young's modulus E1 3 107 3 107 kN/m2
Poisson's ratio υ1,2 0 0 -
α 0.2320 0.2320 -
Rayleigh damping
β 8 10 -3
8 10-3 -
Two different material datasets are used for the basement and the rest of the
building. Soil-structure interaction is modeled interms of interfaces at the outer side
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basement . Central columns are constructed as between basement and first floor and
the successive five floors. They are modeled using Node-tonode anchor feachers . The
material dataset is according to Table (4.7).
Table (4.7) Material properties of node-to-node anchor (after PLAXIS 3D Manual,

2013).
Parameter Name Column Unit
Material type Type Elastic -
6
Normal stiffness EA 2.5 . 10 kN
4.6.3 Loading Model

Wind load is simulated by applying a static lateral force of 1 kN/m is applied
laterally at the top left corner of the building.Earthquake is modeled by imposing a
prescribed displacement at the bottom boundary of the model, earthquake data is
available by PLAXIS knowledge base shown in Figure (4.17).
Figure (4.17) Earthquake data (after PLAXIS 3D Manual, 2013).
4.6.5 Performing Calculations

The calculation process consists of
- Initial Phase is the first phase generated to calculate Soil stresses.
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- Second Phase is generated to calculate Plates, Interfaces and anchors (Construction

of the Building).
- Third Phase the line load (wind load) is calculated .
- Fourth Phase the type of calculation is selected as Dynamic, setting the time interval
to 5 s. The line load is deactivated and the default dynamic boundary conditions are
changed , boundary Ymax,min changed to None and boundary Zmin to viscous.
- Fifth Phase Earthquake calculations are implemented , this phase is started from
Phase-1 , type of calculation is selected as Dynamic, setting the time interval to 20 s.
After resetting displacement to zero , activating Surface displacement and its
dynamic component. The Zmin boundary is not viscous in this phase. Before starting
calculations, points for load displacement curves are to be selected and they are: (0
1.5 15), (0 1.5 6), (0 1.5 3) and (0 1.5 -2), as shown in Figure (4.18).
Figure (4.18) Names of the selected points.
4.6.6 Veiwing the Results

After performing calaulations for the three models (HS small, MC with and
without damping) the time history of displacements of point A (0 1.5 15) for
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earthquake phase were described in Figure (4.19), it is seen that the vibration decays
slowly with time due to damping in the soil and in the building.
Figure (4.19) Time history of the displacements of point (A) at the top of the building
due to earthquake for HS small model and Mohr-Coulomb model with and without
damping.
In the HS small model stiffness introduces hysteretic damping when used in

dynamic applications, the amount of damping depends on the applied load amplitude
and corresponding strain amplitudes (PLAXIS 3D Manual, 2013). The undamped
Mohr-Coulomb model introduces a higher displacement at point A and shows
undesirable deflection shape , as shown in Figures (4.19) and (4.20), after introducing a
damping ratio of ξ = 5% to Mohr-Coulomb model the results were so close to HS small
model , as shown in Figures (4.19) and (4.20). Concluding that Mohr-Coulomb model
is a suitable model for simulating soil profiles under dynamic excitation.
85
HS small model MC model no damping MC model with damping
Figure (4.20) The deflected shape for HS small model and Mohr-Coulomb model
with and without damping.
86
CHAPTER FIVE Parametric Study
CHAPTER FIVE
Parametric Study
5.1 Introduction
In chapter three the database for soil parameters of seismic active zones in Iraq
which are required for Mohr- Coulomb model in addition to the strongest earthquake
occur in Iraq for the latest five years were prepared in order to be used in this chapter
as input data for simulation of soil-pile interaction under the effect of earthquake using
PLAXIS 3D 2013 software checked and verified in chapter four. Twenty models are
simulated for five different zones in Iraq (North, Middle, Western south, Eastern south
and South). Both the bending moment and horizontal displacement results with depth
of pile are evaluated. Then a parametric study is performed for the site where the
maximum bending moment and horizontal pile deflection curvature are predicted, and
the effects of pile length, diameter and stiffness are investigated together with the
influence of different earthquake accelerations.
5.2 Seismic Behavior of Pile in Iraq Soils

A PLAXIS 3D 2013 model of a single pile embedded in a 40×30×25 soil model
is simulated in order to study the effect of earthquake on piles in Iraq soils.
5.2.1 Geometry Model

A typical geometry and soil layers model together with the embedded pile, point
load and prescribed displacements are given in Figure (5.1). The model dimensions are:
X=40 m, Y= 30 m and Z=25 m as shown in Figure (5.1, a). The available geophysical
investigations reports providing dynamic parameters of maximum depths 10m-22m for
different sites in Iraq, from the data base the last layer for each site is extended to have
a total model depth of 25m.
5.2.2 Soil Modeling

The soil is simulated as Mohr-Coulomb model. Drainage type is set as
undrained A. Soil parameters (c, φ, γ, Vp , Vs , Ed , Gd and ν ) , layers depths and water
table levels are taken from different zones (North, Middle, Western south, Eastern
78
south and South) of Iraq as mentioned in Table (3.2). Assuming Damping ratio ξ = 5%
according to PLAXIS 3D Manual (2013), Eurocode 8 (2004), FEMA (2012) and PISC
(2013).
Clayey Silt Embedded pile

30 m 1m
Clay
14 m
40m
25 m Sand 10 m
Lp=20 m
Dp=1 m
Earthquake
prescribed displacement
(a) (b)
Figure (5.1) (a) Geometry and soil layers model (b) Embedded pile, point
load and the prescribed displacement of M5 site in Baghdad.
5.2.3 Pile and Point Load Modeling

The embedded pile of 1 (m) diameter and 20(m) length is simulated as linear-
elastic model, material properties are shown in Table (5.1). The soil-pile interaction
was modeled by the interface element. The allowable bearing capacity of the pile for
each site is calculated (Appendix, A) then entered as base resistance Fmax in (kN) and
skin resistance Ttop,max and Tbot,max in (kN/m) divided by pile length. A point load is
inserted at pile head, its magnitude equals to the bearing capacity of the pile Npile which
is calculated according to 3D PLAXIS Manual (2013).
Npile=Fmax + ½ Lp ( Tbot,max + Ttop,max ) (5.1)
where Lp is the length of pile .
Table (5.1) Material properties of the embedded pile.

Pile Length, Lp Dia., Dp
γp (kN/m3) Ep (kN/m2) νp
Material (m) (m)
Concrete 20 1 24 3x107 0.15
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5.2.4 Earthquake Modeling

The strongest earthquake in south of Iraq hit Ali Al-Gharbi in Missan Province on
April 20, 2012 shown in Figure (4.14) is to be considered as input dynamic prescribed
displacement applied at the bedrock level along the x- direction of the model in the
form of acceleration-time readings in (m/s2) and (s) respectively, during 60 seconds as
a reading for each 0.1 second. Figure (5.2) shows that the maximum acceleration
recorded during the first 20 seconds of the earthquake.
Figure (5.2) Acceleration – time records of earthquake hit Ali Al-Garbi in

Missan on April 20,2012 during 60 seconds.
5.2.5 Boundary Conditions of the Model

The boundary conditions of the geometry model are as in the following:
• Vertical boundaries with their normal in x -direction (i.e. parallel to the yz -
plane) are fixed in x -direction (ux= 0) and free in y- and z-direction.
• Vertical boundaries with their normal in y -direction (i.e. parallel to the xz -
plane) are fixed in y -direction (uy= 0) and free in x- and z -direction.
• Vertical boundaries with their normal neither in x- nor in y-direction are fixed
in x - and y -direction (ux= uy= 0) and free in z-direction.
• The model bottom boundary is fixed in all directions (ux= uy= uz= 0).
78
• The 'ground surface' is free in all directions.

• In order to prevent waves' reflection, absorbent boundary conditions applied
on the model vertical boundaries to absorb outing waves (3D PLAXIS Manual, 2013),
using viscous option for boundary Xmax,min and Ymax,min and None for boundary Zmax,min
for bedrock roof.
5.2.6 Mesh Generation

Due to the large model’s dimensions, medium mesh was created. The mesh
consists of nearly (27319) elements (10-node tetrahedrons) with over than (40676)
nodes as shown in Figure (5.3).
Figure (5.3) Mesh generation for M5 site.
5.2.7 Performing Calculations

Calculations are performed by dividing the calculation process in to multi
phases.
- Initial phase is generated to calculate initial stresses of soil layers and pore water
pressure. In PLAXIS 3D 2013 K0 procedure is a special calculation method
available to define the initial stresses for the model, for Mohr Coulomb the default
89
K0 - value is suitable based on Jaky's empirical expression where K0 is related to the

friction angle as (3D PLAXIS Manual, 2013):
K0=1-Sinϕ (5.2)
- First phase generated to calculate pile stresses using plastic calculation method.
- Second phase generated to calculate the point load.
- In the Third phase, the dynamic calculations are implemented to calculate
earthquake stresses. To analyze the maximum values of Ali Al-Garbi earthquake
accelerations, set time interval to 20 (s), select the reset displacement to zero
parameter, this will remove the effect of the initial stress generation procedures or
the plastic calculation phase on displacement developed during subsequent
calculations, whereas the stresses remains (3D PLAXIS Manual, 2013) .
- Execute the calculation.
5.3 Influence of Soil Dynamic Parameters on the Behavior of Pile

The results show that the maximum bending moment occurs at N2 site in North
zone , M5 in Middle zone , WS1 in Western south zone, ES2 in Eastern south zone and
S5 in South zone.
Values of bending moments are varied along pile length with zero moment at
pile tip and head, values in between are either positive or negative or both which
depends on soil type, number and depths of soil layers as shown in Figures (5.4), (5.5),
(5.6), (5.7) and (5.8). The maximum bending moment value is 2699.617 (kN.m) at
depth 15 (m) for M5 site. The bearing capacity of 4000(kN) for this site was the
maximum bearing capacity among the other sites. It can be indicated that the
maximum bending moment is obtained at the interface between the clay and sand
layers located at depth of 15(m) from ground surface as shown in Figure (5.1).
Rajapakse )2008) indicated that the pile under earthquake is subjected to differential
forces due to different seismic waves arriving in two soil layers. Kinematic pile
bending can occur in homogeneous soils as well, owing to the fact that seismic wave
forms can have different strengths depending on soil layer depth and surrounding
structures that could damp the wave in a non-uniform manner, the maximum bending
89
moment occurs at the interface of two soil layers due to the different wave velocity of
soil layers.
From Table (3.2) the data base shows that the values of compression and shear
velocities are higher in sandy soils than in clayey soils and the highest difference in
shear and compressional wave velocities for the different successive soil layers occurs
at M5 site. The maximum value of bending moment occur at interface of different soil
layers as the compressional or shear wave passes from sandy soil of higher wave
velocity to the clayey soil of the lower wave velocity. In most of soil profiles both
wave velocities are increased with depth. The frictional nature (cohesion for clay and
angle of internal friction for sand) is that the strength depends on the effective stresses
in the soil. As the effective stresses increase with depth, so in general will the strength,
concluding that the shear and compressional wave velocities are increased in
proportion with soil strength.
Mylonakis and Nikolaou (2002) classified the curvatures and subsequent
bending imposed to piles by the surrounding soil during the passage of strong seismic
waves into (a) bending moment due to the up and down- propagating waves in the soil
(“kinematic” bending) and (b) bending moment due to liquefaction and subsequent
lateral soil movement (“liquefaction-induced” bending) as shown in Figure (5.9).
In the present study when the pile tip embedded through sand or gravel soil with
clayey soil for the upper layers the bending moment values are positive at pile tip and
goes negative at the upper layers for (N2, M1, M2, M5 and WS2) sites.
For soil profiles consist of multi sandy soil layers, bending moment values are
positive along pile length for (WS1, WS3 and S5) sites.
For soil profiles consist of multi clayey soil layers or clayey layer at pile tip with
sandy upper layer bending moment values are negative at pile tip then goes positive at
upper layers for (N1, N3, ES1, ES2, ES3, S1, S2, S3 and S4) sites.
The shapes of the bending moment profiles indicate that the deformed shape of
the pile had a double curvature caused by the top and bottom soil layers loading the
pile in opposite directions. The double curvature shape indicates that the non-liquefied
shallow layer pushed the pile laterally resisting this bending action (Muthukkumaran
and Subha, 2010).
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Bending Moment (kN.m)

-2000 -1500 -1000 -500 0 500
0
North
5
N1
N2
N3
10
Depth (m)
15
20
25
Figure (5.4) Bending moment diagrams of pile for North zone.

-3000 -2000 -1000 0 1000 2000 3000
0
Middle M1
5 M2
M3
M4
M5
10 M6
Depth (m)
15
20
25
Figure (5.5) Bending moment diagrams of pile for Middle zone.
89
Bending Moment( kN.m)

-2000 -1500 -1000 -500 0 500 1000 1500 2000 2500
0
Western south
10
Depth (m)
15
WS1
WS2
20 WS3
25
Figure (5.6) Bending moment diagrams of pile for Western south zone.

-1200 -1000 -800 -600 -400 -200 0 200
0
Eastern south
5
ES1
ES2
ES3
10
Depth (m)
15
20
25
Figure (5.7) Bending moment diagrams of pile for Eastern south zone.
89

-400 -200 0 200 400 600 800 1000
0
South
5
10
Depth (m)
15 S1
S2
S3
S4
20
S5
25
Figure (5.8) Bending moment diagrams of pile for South zone.
Figure (5.9) Bending moment diagram of single pile without superstructure under
seismic excitation (a) Kinematic bending. (b) Liquefaction- induced bending (after
Mylonakis and Nikolaou, 2002).
According to soil-pile interaction, pile horizontal displacement, ux occurs due to

movement of the surrounding soil particles under seismic excitation. Figures (5.10),
(5.11), (5.12), (5.13) and (5.14) show the horizontal displacement of single pile which
is imbedded in different soil layers and for different zones in Iraq.
89
The results were examined well and it was found that the profile of maximum bending
moment for M5 site gives maximum curvature of the deflected shape as shown in
Figure (5.11), while the maximum horizontal displacement value is evaluated at M3 site
in the middle zone soils of Iraq as shown in Figure (5.11), knowing that this site gives
minimum bending moment values in Figure (5.6), with site soil classification of type E
as shown in Table (3.7), a soft clay soil according to PISC (2013) and FEMA (2010).
The horizontal displacement of the embedded pile is affected by type of soil,
number and depth of soil layers also the difference in wave velocity for the successive
soil layers. From Figures (5.11), (5.12) and (5.14) it is seen that the deflected shape of
pile embedded in sand soil models have the same behavior for (M6, WS1, WS3 and S5)
sites.
The deflected shapes of piles embedded in clayey soil are shown in Figures
(5.10) and (5.13); ( N1, N2, N3, ES2 and ES3) sites.
From Figures (5.13) and (5.14) the deflected shape of pile in two clayey soil
layers with thin sandy layers in between as in (ES1,S1, S3 and S4) sites.
ux /Dp
0% 5% 10% 15% 20% 25%
0
North
5
N1
N2
10 N3
Depth (m)
15
20
25
Figure (5.10) Horizontal displacement of pile per diameter with depth for North
zone.
89
ux /Dp
0% 5% 10% 15% 20% 25% 30%
0
Middle
5 M1
M2
M3
10 M4
Depth (m)
M5
M6
15
20
25
Figure (5.11) Horizontal displacement of pile per diameter with depth for
Middle zone.
ux/Dp
0% 5% 10% 15% 20% 25%
0
Western South
5 WS1
WS2
WS3
10
Depth (m)
15
20
25
Figure (5.12) Horizontal displacement of pile per diameter with depth for
Western south zone.
88
ux/Dp
0% 5% 10% 15% 20% 25%
0
Eastern South
5
ES1
ES2
10 ES3
Depth (m)
15
20
25
Figure (5.13) Horizontal displacement of pile per diameter with depth for Eastern
south zone.
ux/Dp
0% 5% 10% 15% 20% 25% 30%
0
South
5 S1
S2
S3
10 S4
Depth (m)
S5
15
20
25
Figure (5.14) Horizontal displacement of pile per pile diameter with depth for
South zone.
87
5.4 Parametric Study
In order to come up with pile design requirements under seismic excitation

according to FEMA (2012) and PISC (2013), piles and piers should be designed to
withstand the maximum structural loads and the curvature of pile results from
earthquake ground movement and the response of the superstructure. These curvatures
should include the free field motion of soil and the soil-pile interaction associated with
deflections of pile or pier results from horizontal seismic excitation.
Pile bending moment consider both inertial and kinematic interaction of pile in
which the stiffness of the foundation system impedes development of free-field ground
motion. Differences of pile responses occur not only at the pile head but also at the
boundary of the soil layer, the pile bending moment near the pile head is induced by the
inertial force of the superstructure, and that at the soil boundary is induced by soil
displacement (Miyamoto, 2000). A model of pile embedded in M5 site soil model is
chosen for the parametric study since this model evaluated the maximum bending
moment value as shown in Figure (5.6) and maximum pile deflection curvature as
shown in Figure (5.11). The model is simulated using PLAXIS 3D 2013 program. The
model geometry, soil modeling, pile and point load modeling, earthquake modeling,
boundary conditions and mesh generation were as mentioned in sections (5.2.1),
(5.2.2), (5.2.3), (5.2.4), (5.2.5) and (5.2.6) respectively. The calculation phases were
simulated as in section (5.2.7), select node points A (20,15,0), B(20,15,-1), C(20,15,-
15) and D(20,15,-20) before executing the calculation then evaluating the results.
To examine the soil-pile interaction, the horizontal displacement of soil layers
shown in Figure (5.15) is compared with the horizontal displacement of the pile in M5
site shown in Figure (5.11). The maximum and minimum horizontal soil deflection ux
were 0.259 m and 0.0612 m respectively.
The plastic points shown in Figure (5.16) are concentrated at the interface area
between soil layers and around the pile surface which proves the nonlinearity of soil
pile behavior under seismic excitation and the validity of applying Mohr-Coulomb soil
model in this study.
88
Figure (5.15) Horizontal displacement of soil layers.
Figure (5.16) Plastic points of the model (a) three dimensional model. (b)
longitudinal cross section of the model at 15 m in the y-axis.
999
Due to end bearing action which is effective more than horizontal forces action
at pile tip the maximum shear stress in the soil occurs at the pile tip as shown in Figure
(5.17).
Figure (5.18) shows the horizontal displacement ux of points (A, B, C and D)
during the earthquake, it is found that the greatest horizontal displacement occurred for
point D at pile tip which is the nearest point to the earthquake, the lowest horizontal
displacement occurred in point A at ground surface due to damping of soil layers. Also
three peaks of the horizontal displacements appears at dynamic times 6.5, 13 and 19
sec.
Figure (5.17) Maximum shear stresses for the soil cross section at 15m in the y-
axis.
999
Figure (5.18) The horizontal displacement ux for node points (A, B, C and D) with
dynamic time.
5.4.1 Effect of Pile Length Lp

To study the bending moment for different pile lengths (Lp= 5,10,12,15,18 and
20 m) which is embedded in a model for site M5, as shown in Figure (5.19) that
maximum bending moment occurred at 15 m depth (i.e., the interface between the clay
and sand layers) for Lp= 18 and 20 m, for Lp= 10,12 and 15m in which the pile passes
through a 1 m sandy layer and 14 m clayey layer the maximum bending moment
occurred at 7-8 m depth at about half the clay layer depth, while for Lp=5m the
bending moment values are very small and the maximum value (21.41 kN.m) occurred
at 2.6 m depth about half the pile length.
It can be indicated that the maximum negative bending moment is increased
when the length of pile is increased until pile length reaches 15 m then the pile passes
to the sandy layer where the interface of two layers becomes effective, in this case
when the length of pile increased the negative moment is decreased and the positive
moment is increased. In general, higher pile length gives larger bending moment.
999

-3000 -2000 -1000 0 1000 2000 3000 4000
0
Lp=20 (m)
Lp=18 (m)
5 Lp=15 (m)
Lp=12 (m)
Lp=10 (m)
Lp=5 (m)
10
Depth (m)
15
20
25
Figure (5.19) Bending moment diagrams using different pile lengths.
Figure (5.20) shows the effect of different pile lengths on the horizontal
displacement, ux of the pile, for Lp= 18 and 20 m the deflected shape has two opposite
curvature angle because the pile is embedded through two different soil layers 14 m
clayey layer and 10 m sandy layer assume that the 1m upper sandy soil layer is
ineffective, for Lp= 10,12 and 15m the pile is embedded in clayey layer and the
deflected shape of single curvature. For Lp=5m the deflected shape is linear as
Lp/Dp=5< 6 in this case the pile is considered as a rigid pile that resists curvatures with
respect to soil movement according to PISC (2013).
Figure (5.21) shows the effect of pile length on the vertical displacement, uz of
pile head, it can be indicated that the vertical deflection of pile head increases as pile
length is increased under the earthquake action and the same point load value.
The results presented that the vertical deflection is little affected by increasing
the pile length from 5m to 10m while for length higher than 10m the deflection
increased with higher rate being enlarged by about ten times when the length of pile is
duplicated.
999
ux/Dp
0% 5% 10% 15% 20% 25%
0
10
Depth (m)
15
Lp=20 (m)
Lp=18 (m)
Lp=15 (m)
20 Lp=12 (m)
Lp=10 (m)
Lp=5 (m)
25
Figure (5.20) Horizontal displacement as a percentage of pile diameter using

different pile lengths.
12%
10%
8%
uz/Dp
6%
4%
2%
0%
0 5 10 15 20 25
Lp (m)
Figure (5.21) Vertical displacement of pile head as a percentage of the pile

diameter for different pile lengths.
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5.4.2 Effect of Pile Diameter Dp

Figure (5.22) shows the bending moment diagrams for different pile diameters
(Dp= 0.6, 0.8, 1, 1.2, 1.5, 2m) embedded in a model for site M5. It can be indicated that
there is an increasing in bending moment value with increasing the pile diameter. The
maximum bending moment is also increased with increasing diameter. It has been
observed that the maximum bending moment for 0.6m diameter pile is about 90% less
than that for 2m diameter, and the increasing is almost linear as indicated in Figure
(5.23).
Figure (5.24) shows the horizontal pile displacement for different pile diameters
and the results show that the minimum and maximum values are the same but the pile
deflection curve reduced when the pile diameter was increased, this means that when
L/D decreased and becomes close to 6 the pile behaved as a rigid pile according to
PISC (2013).

-6000 -4000 -2000 0 2000 4000 6000 8000 10000
0
Dp=0.6 (m)
Dp=0.8 (m)
5 Dp=1 (m)
Dp=1.2 (m)
Dp=1.5 (m)
Dp=2 (m)
10
Depth (m)
15
20
25
Figure (5.22) Bending moment diagrams using different pile diameters.
999
2.5
Dp (m) 1.5
0.5
0
0 2000 4000 6000 8000 10000
Max.Bending Moment (kN.m)
Figure (5.23) Maximum bending moment for different pile diameters
ux/(Dp=1m)
0% 5% 10% 15% 20% 25%
0
10
Depth (m)
15 Dp=0.6(m)
Dp=0.8(m)
Dp=1 (m)
20 Dp=1.2 (m)
Dp=1.5 (m)
Dp=2(m)
25
Figure (5.24) Horizontal displacement of pile as a percentage of 1m diameter using
different pile diameters
The vertical displacement of pile head decreased with increasing the pile
diameter as shown in Figure (5.25). The displacement caused by earthquake can be
decreased by about 70% with increasing pile diameter from 0.6m to 2m.
999
1.2%
1.0%
0.8%
uz/(Dp=1m)
0.6%
0.4%
0.2%
0.0%
0 0.5 1 1.5 2 2.5
Dp (m)
Figure (5.25) Vertical displacement of pile head as a percentage of 1m diameter for

different pile diameters
5.4.3 Effect of Modulus of Elasticity Ep

In areas where earthquakes are of concern the stiffness plays a key role when
evaluating liquefaction potential, estimating soil amplification and when defining
earthquake loading (Bessason and Erlingsson, 2011). To study the effect of stiffness EI
on bending moment and horizontal deflection of pile, different modulus of elasticity for
concrete pile Ep is to be applied on M5 site model, according to ACI Code (2008)
modulus of elasticity for concrete Ep with normal weight and normal density is given
by;
√ (5.3)
where fc' is concrete compressive strength at 28 days. For different values of (fc'
= 24, 28, 35 40 and 45 MPa ) the evaluated (Ep = 23, 25, 28, 30 and 32 GPa ).
Figure (5.26) shows the bending moment diagrams for pile using different
modulus of elasticity and the results show that the diagrams have the same behavior
and the maximum bending moment values increased with increasing modulus of
elasticity. It has been observed that the moment increased by about 20% with
increasing modulus of elasticity by about 40%, and the increasing is linear as indicated
in Figure (5.27) which shows the increasing in maximum bending moment of the pile
with the increasing in the pile modulus of elasticity.
998

-3000 -2000 -1000 0 1000 2000 3000 4000
0
Ep=32 Gpa
Ep=30 Gpa
5
Ep=28 Gpa
Ep=25 Gpa
Ep=23 Gpa
10
Depth (m)
15
20
25
Figure (5.26) Bending moment diagrams using different pile modulus of elasticity.
35
30
25
Ep (GPa)
20
15
10
5
0
2500 2600 2700 2800 2900 3000 3100 3200
M (kN.m)
Figure (5.27) Maximum bending moment for different pile stiffness.
Figure (5.28) shows that the use of different modulus of elasticity values has
insignificant effect on the horizontal displacement of pile. Also no announcement
influence of modulus of elasticity on vertical displacement of pile head is predicted
as shown in Figure (5.29).
997
ux/Dp
0% 5% 10% 15% 20% 25%
0
10
Depth (m)
15
Ep=32 Gpa
Ep=30 Gpa
20 Ep=28 Gpa
Ep=25 Gpa
Ep=23 Gpa
25
Figure (5.28) Horizontal displacement as a percentage of pile diameter using
different pile modulus of elasticity
0.796%
0.794%
0.792%
0.790%
uz/Dp
0.788%
0.786%
0.784%
0.782%
0.780%
0 5 10 15 20 25 30 35
Ep (GPa)
Figure (5.29) Vertical displacement of pile head as a percentage of the pile
diameter for different pile stiffness
5.4.4 Effect of earthquake Acceleration

The records of the strongest earthquake in south of Iraq hit Ali Al-Gharbi in
Missan Province on April 20, 2012 with peak ground acceleration of 104.151 cm/sec2
(0.11 g) and ML = 5 magnitude according to Richter scale as described in Table (3.5) is
used in this study. Accelerations are typically measured in units of g, where g is the
acceleration due to gravity on the surface of the Earth. Typical accelerations in
998
earthquakes are between 0.05 and 1 g. Acceleration is often the primary consideration
in looking at shaking because it determines how much force an earthquake impacts on
a building, and thus if a building will stand. Since shaking is one of the primary causes
of damage, there is a clear trend of higher accelerations causing greater damage and
therefore greater intensities. As a result there is a correlation between acceleration and
Mercalli Intensity (Baer, 2007). In this section the effect of increasing acceleration
intensity on a pile embedded in a model for site M5 is investigated. Figure (5.30) shows
the effect of increasing acceleration readings, a of Ali Al-Gharbi earthquake as (1.2,
1.5, 2, 2.5, 3 and 5) times a on the bending moment. The results show the same
behavior for bending moment diagrams at 1.2a, 1.5a, 2a and 2.5a increasing in
acceleration of earthquake and when reaches 3a and higher the bending moment shows
undesirable decreasing in positive values and increasing in negative values.
The horizontal displacement of pile increased at pile tip with insignificant
influence on pile head for 1.2a, 1.5a, 2a and 2.5a increasing in acceleration as shown
in Figure (5.31), but for 3a and higher the deflected shape show a behavior similar to
the behavior for the pile deflected in liquefied soils, and according to the three
distinctive failure mechanisims in piles proposed by Meyersohn (1994) shown in
Figure (2.19) the failure occurred due to excessive rotation of the pile. It can be
suggested that with increasing soil movement, this form of pile response may be
followed by the formation of a plastic hinge, or by a premature collapse of the
foundation due to a combination of excessive rotation and lack of lateral support. From
the bending moment and deflection results it can be concluded that failure occurs in
cohesive soil due to the formation of a failure wedge near the ground surface, a gap
between the ground and the pile and the flow of the soil around the pile when the
acceleration is three times that of Ali Al-Gharbi earthquake and the peak ground
acceleration = 312.453 cm/sec2 (0.32 g) raising the magnitude of earthquake to about
ML=6.6 according to the relationship between magnitude and acceleration of
earthquake given by Donovan (1973):
(5.4)
where a is acceleration in cm/sec2, M is Richter magnitude and D is distance in km.
999

-8000 -6000 -4000 -2000 0 2000 4000 6000
0
Ali Al-Gharbi acc., a
1.2 a
1.5 a
5
2.0 a
2.5 a
3.0 a
10 5.0 a
Depth (m)
15
20
25
Figure (5.30) Bending moment diagrams for earthquake acceleration.
ux/Dp
0% 20% 40% 60% 80% 100% 120%
0
Ali Al-Gharbi acc., a

1.2 a
5 1.5 a
2.0 a
2.5 a
10 3.0 a
Depth (m)
5.0 a
15
20
25
Figure (5.31) Horizontal displacement of pile as a percentage of diameter using
different earthquake acceleration.
999
CHAPTER SIX Conclusions and Recommendations
CHAPTER SIX
Conclusions and Recommendations
6.1 Introduction
In this study a data base for the dynamic properties of different soils for seismic
active zones in Iraq was prepared. The properties of soils were then used as input
dynamic data for finite element program PLAXIS 3D 2013 to study the response of
single pile embedded in different Iraq soils under seismic excitation of the influential
earthquake in south of Iraq hits Ali Al-Gharbi in Missan Province on April 20, 2012.
Finally a parametric study was made to investigate the influence of pile length,
diameter and stiffness on the seismic behavior of pile together with the effects of the
acceleration – time records for earthquake.
6.2 Conclusions
From the present study, the following conclusions may be drawn:
1. The compressional and shear wave velocities estimated, as well as, the
corresponding average dynamic moduli for soil layers are given in Table (3.2),
together with the soil parameters γwet ,γdry , c and ϕ evaluated. Thus, database of the
soil and dynamic parameters for seismic active zones in Iraq are prepared to be
used as input data for simulation of piles under earthquake effects using FEM
softwares.
2. The average compressional wave velocity was ranged from (1125-2500) m/s in the
North, (306-1544) m/s in the Middle, (805-1812) m/s in the Western south, (377-
1326) m/s in the Eastern south and (334-1404) m/s in the South of Iraq. While the
shear wave velocity was ranged from (225-476) m/s in the North, (111-408) m/s in
the Middle, (268-659) m/s in the Western south, (131-380)m/s in the Eastern south
and (102-365) m/s in the South of Iraq.
3. Dynamic modulus of elasticity was ranged from (290.15-1409.8) MN/m2 in the
North, (57.9-1107.4) MN/m2 in the Middle, (457-2472.2) MN/m2 in the western
south, (90.15-1082.8) MN/m2 in the eastern south and (61.8-682.52) MN/m2 in the
South of Iraq. Also, the dynamic shear modulus of elasticity was ranged from
111
(98.09-475.98) MN/m2 in the North, (20.33-378.73) MN/m2 in the Middle, (154.6-

868.03) MN/m2 in the western south, (31.5-374.17) MN/m2 in the eastern south and
(21.23-233.14) MN/m2 in the South of Iraq.
4. Iraq sites soils were classified according to different seismic codes depending on
Vs,30 value. According to PISC (2013) and FEMA (2010) the sites soils are
classified as types (E,D and C) while according to Eurocode 8 (2004) sites soils are
classified as types (D, C and B) concluding that Iraq soils are ranging between;
Very dense soil , soft rock or gravel for WS1 and WS3 sites of the Western south
zone to soft clayey soil or loose-to-medium cohesionless soil for M3 site of the
Middle zone and S3 and S4 sites of South zone in Iraq.
5. The research showed the susceptibility of PLAXIS 3D 2013 program in analyzing
piles with different soil conditions under earthquake action. And the results showed
the importance of studying seismic behavior of soil-pile system using 3-D analysis
rather than 2-D analysis because the problem is truly 3-D and should be analyzed as
such.
6. The maximum bending moment during earthquake occurs at the interface of
different soil layers for each soil profile along the pile depth, thus the kinematic
pile moments occurs at relatively deep interfaces between soil layers with very
different stiffnesses. Concluding that the shear and compression wave velocities
play an important role in estimating the dynamic behavior of piles and design of
foundations.
7. Maximum bending moment value is 2699.617 (kN.m) evaluated at depth 15 (m) at
the interface of sand and clay soil layers for M5 site. The values of compression and
shear waves velocities are higher in sandy soils than in clayey soils and the highest
difference in shear and compressional wave velocities for the different successive
soil layers occurs at M5 site. Concluding that the maximum bending moment occurs
at the interface of two soil layers due to the different wave velocity of soil layers.
8. For soil profiles consist of clayey soil for the upper layers and sand or gravel soil
for the lower layer the bending moment values were positive at pile tip change to
negative at the upper layers for (N2, M1, M2 and WS2) sites. And for soil profiles
consist of multi sandy soil layers, bending moment values were positive along pile
111
length for (WS1, WS3 and S5) sites. While for soil profiles consist of multi clayey
soil layers or clayey layer at pile tip with sandy upper layer bending moment values
were negative at pile tip then goes positive at upper layers for(N1, N3, ES1, ES2,
ES3, S1, S2, S3 and S4) sites.
9. According to soil-pile interaction, pile deflection occur due to movement of the
surrounding soil particles under seismic excitation, the deflected shape have the
same behavior for pile embedded in sand soil models as in (M6, WS1, WS3 and S5)
sites. Also for pile embedded in clayey soil as in (N1, N2, N3, ES2 and ES3) sites. As
well as the pile that embedded in two clayey soil layers with thin sandy layers in
between as in (ES1,S1, S3 and S4) sites.
10. The plastic points are concentrated at the interface area between soil layers and
around the pile surface which proves the nonlinearity of soil pile behavior under
seismic excitation. Also, the greatest and lowest horizontal displacements occurred
at pile tip and ground surface respectively.
11. The parametric study for M5 site shows that the maximum shear stress in the soil
occurs at the pile tip due to end bearing action which at pile tip is effective more
than horizontal forces.
12. When pile length increased, the horizontal deflection with the deflected curve is
increased due to increasing Lp/Dp ratio. The results presented also that the vertical
deflection is little affected by increasing the Lp/Dp ratio from 5 to 10 while for ratio
higher than 10 the deflection increased with higher rate being enlarged by about ten
times when increasing the length of pile two times.
13. There is increasing in bending moment value with increasing pile diameter. As
well as the maximum bending moment is increased with increasing diameter,
knowing that for 0.6m diameter pile the maximum bending moment is about 10%
of that for 2m diameter. For the horizontal pile deflection the minimum and
maximum values are the same for different pile diameters but the pile deflection
curve reduced when the pile diameter was increased, it means that when L p/Dp
decreased and becomes close to 6 the pile behaved as a rigid pile. While the vertical
displacement of pile head decreased with increasing the pile diameter. The
111
deflection caused by earthquake can be decreased by about 70% with increasing

pile diameter from 0.6m to 2m.
14. It has been observed that the moment increased by about 20% with increasing
modulus of elasticity of pile material by about 40%, and the increasing is linear.
While the use of different modulus of elasticity values has insignificant effect on
the horizontal deflected shape of pile. Furthermore no announced influence of
modulus of elasticity on vertical displacement of pile head is predicted.
15. In Middle zone the soil-pile system cannot sustain earthquake of magnitude
ML=6.6 with peak ground acceleration (0.32 g) with the formation of a failure
wedge near the ground surface, a gap between the ground and the pile and the flow
of the soil around the pile.
6.3 Recommendations
The following recommendations for the future research:
1. Expand the study to cover other seismic active zones of Iraq especially at Duhok,
Sulaimaniya, Erbil, Mousel , Diyala , Waset …etc.
2. Updating the data base with new geophysical and geotechnical investigation data.
3. A parametric study can be carried out to study the seismic excitation on pile group.
4. A parametric study can be carried out to predict the effect of different pile cross
sectional shape.
5. The study can be applied on piles or piers for existing structures in the investigated
zones to check their stability under earthquake loads. Also, the maximum
magnitude (ML) of earthquake that can be sustained by piles can be obtained in
these zones.
6. It is useful to investigate the influence of using other types of models representing
soils in PLAXIS program rather than Mohr-Coulomb model such as Hardening
Soil (HS small) and Modified Cam-Clay (MMC) models.
7. The dynamic soil parameters can be evaluated experimentally using dynamic
triaxial test and the data base can be updated accordingly.
8. Experimental study model using table shaking device are essential in approving a
better understanding of the seismic behavior of piles.
111
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121
APPENDIX A Single Pile Capacity Calculation
APPENDIX A
Single Pile Capacity Calculation
A.1 Introduction
In this appendix, and as a requirement within the frame of this study, a
description of the calculation of the single pile capacity in each active seismic zone
in Iraq is carried out. Pile used in this study has different diameter and length, and
thus the capacity of single pile depend on its dimensions, and soil properties of
surrounding the pile which consider a main factor effect on the pile capacity.
A.2 Bearing capacity of single pile

The bearing capacity of single pile is the sum of its shaft bearing capacity and its
end bearing capacity. There are two usual approaches to the calculation of the
ultimate load capacity of piles: the "static" approach, which uses the normal soil-
mechanics method to calculate the load capacity from measured soil properties; and
the "dynamic" approach, which estimates the load capacity of driven piles from
analysis of pile- driving data. In this study will use the static approach to calculate
ultimate load capacity of pile (Poulos and Davis, 1980)
In PLAXIS 3D 2013 program, the allowable load capacity of single pile will be
simulated with a factor of safety:
Qal : Qul/2 (A.1)
Where:
Qal: allowable load capacity of single pile
Qul: ultimate load capacity of single pile
The net ultimate load capacity, Pu, of a single pile is generally accepted to be equal
to the sum of the ultimate shaft and base resistances, less the weight of the pile; that
is,
Pu : Psu +Pbu - W (A.2)
Where:
A-1
Psu : ultimate shaft resistance

Pbu : ultimate base resistance
W : weight of pile
Psu can be evaluated by integration of the pile-soil shear strength τa over the surface
area of the shaft. τa is given by the Coulomb expression:
τa = ca + σn . tan Øa (A.3)
where
τa : pile-soil shear strength
ca : adhesion
σn : normal stress between pile and soil
Øa : angle of friction between pile and soil
σn is in turn frequently related to the vertical stress σv as:
σn = Ks . σv (A.4)
where
Ks : coefficient of lateral pressure
Thus,
τa = ca + σv Ks . tan Øa (A.5)
∫ ∫ (A.6)
where
C : pile parameter
L : length of pile shaft
It is usually accepted that the ultimate resistance Pbu can be evaluated from bearing
capacity theory as:
( ) (A.7)
Where:
Ab : area of pile base
c : cohesion of soil
σv: vertical stress in soil at level of pile base
γ : unit weight of soil
A-2
d : pile diameter
Nc, Nq, Nγ : bearing capacity of factors, which are primarily functions of the angle
of internal friction Ø of the soil, the relative compressibility of the soil and the pile
geometry. From Equations (A.2), (A.3), and (A.7),
∫ ( ) (A.8)
A.3 Calculation of Single Pile Capacity

A.3.1 Pile in clay
For piles in clay, the undrained load capacity is generally taken to be the critical
value. If the clay is saturated, the undrained angle of friction Øu is zero, and Øa,
may also be taken as zero. ln addition, Nq = 1 and Nγ = 0 for Ø = 0, so that
Equation. (A.8) reduces to:
∫ (A.9)
Where;
cu : undrained cohesive of soil at level of pile base
ca : undrained soil-pile adhesion
Further simplification is possible in many cases, since for piles without an enlarged
base, Abσvb = W, in which ,
∫ (A.10)
The soil-pile adhesion factor ca is taken equal to 0.45cu (Poulos, 1980), and bearing
capacity factor Nc was taken equal to 9.
A.3.2 Pile in sand
Conventional methods of calculation of the ultimate load capacity of piles in sand,
assume that the vertical stresses σv and σvb in Equation (A.8) are the effective
vertical stresses caused by overburden,(after Poulos and Davis, 1980).
In sandy soil, the term cNc are taken as zero in Equation (A.8), and the term 0.5γdNγ
is neglected as being small in relation to the term involving Nq, the ultimate load
capacity of single pile in sand may be expressed as follows:
∫ (A.11)
A-3
Where:
σ'v : effective vertical stress along shaft embedment in sand
σ'vb : effective vertical stress at level of pile base
Fw : correlation factor for tapered pile (equal 1 for uniform pile)
Ø'a = 0.75 Øa (A.12)
Ks = (1-sin Øa) (A.13)
The bearing capacity factor Nq is plotted against Ø, for bored pile Ø is taken equal
to Øa -3 , Figure (A.1) relationship between Ø and Nq.
The values of allowable bearing capacity for single pile in different soil profiles for
active seismic zones in Iraq with different lengths and diameters for the parametric
study were calculated and shown in Table (A.1) .
Figure (A.1) The relationship between Ø and Nq.
A-4
Table (A.1) Allowable bearing capacity of single pile.

Site Allowable bearing capacity (kN)
N1 2000
N2 2000
N3 2000
M1 3600
M2 3700
M3 3300
M4 2600
M5 4000
M6 3800
WS1 2000
WS2 2500
WS3 2000
ES1 2000
ES2 1000
ES3 1000
S1 1000
S2 1000
S3 2000
S4 1185
S5 1000
A-5
‫الخالصة‬
‫يقع العراق بالقرب من الطرف الشمالي من الصفيحة العربية التي لها عالقة بالصفيحة األوراسية عند‬
‫التقدم شماالً‪ ،‬ومن المتوقع ان يكون العراق من البلدان النشطة تكتونيا ونتيجة للزيادة الملحوظة للنشاط‬
‫الزلزالي في العراق خالل العقود األخيرة فقد اولى المهندسون اهتماما ً كبيراً في تصاميم األبنية المقاومة‬
‫للزالزل‪.‬‬
‫الركائز من االساسات األكثر استخداما ً في المناطق الزلزالية حيث تكون التربة غير كافية لحمل‬
‫االوزان بمفردها وغالبا ما تمر الركائز من خالل (تخترق) طبقات ضحلة من الترب المفككة و ‪ /‬أو الرخوة ثم‬
‫تستقر نهايتها في تربة ذات قدرة تحمل عالية‪ .‬ولهذا ان دراسة تداخل التربة‪ -‬الركيزة في العراق تحت تأثير‬
‫زلزال واقعي مهمة جدا‪ .‬في هذه الدراسة يتم التحقق من السلوك الزلزالي الثالثي االبعاد للركائز فيالترب‬
‫المختلفة لمناطق نشطة زلزالياً في العراق باستخدام برنامج العناصر المحددة ‪.PLAXIS 3D 2013‬‬
‫ان الخواص الديناميكية تلعب دورا مهما في تصميم المنشآت المعرضة للقوى الزلزالية‪ .‬من احدى‬
‫االهداف الرئيسية من هذه الدراسة هو اعداد قاعدة بيانات للخصائص الديناميكية ألنواع مختلفة من التربة‬
‫للمناطق النشطة زلزاليا في العراق وذلك باالعتماد على نتائج فحصي ‪ cross hole‬و ‪ .down hole‬ومن ثم‬
‫استخدام المعامالت الديناميكية للتربة كمدخالت لبرنامج ‪ ،PLAXIS 3D 2013‬باإلضافة إلى خواص التربة‬
‫التي تم جمعها من أعمال تحريات التربة‪.‬‬
‫لوحظ من قاعدة البيانات التي تم جمعها أن معدل سرعة الموجة االنضغاطية تتراوح بين (‪-2211‬‬
‫‪ )1122‬م‪/‬ثا في المنطقة الشمالية و (‪ )2111-623‬م‪/‬ثا في المنطقة الوسطى و (‪ )2521-521‬م‪/‬ثا في‬
‫الجنوب الغربي و (‪ )2613-633‬م‪/‬ثا في الجنوب الشرقي و (‪ )2121-661‬م‪/‬ثا في المنطقة الجنوبية من‬
‫العراق‪ .‬وكان معدل سرعة موجة القص تتراوح بين (‪ )133-111‬م‪/‬ثا في المنطقة الشمالية و (‪)125-222‬‬
‫م‪/‬ثا في المنطقة الوسطى و (‪ )316-135‬م‪/‬ثا في الجنوب الغربي و (‪ )652-262‬م‪/‬ثا في الجنوب الشرقي و‬
‫(‪ )631-221‬م‪/‬ثا في المنطقة الجنوبية من العراق‪ .‬كما تم تصنيف تربة المواقع في العراق الى أنواع (‪D ،E‬‬
‫و ‪ )C‬وفقا ً لـمواصفات )‪ PISC (2013‬و(‪ ، FEMA )2010‬في حين وفقا لـمواصفات (‪)2004‬‬
‫‪ Eurocode 8‬الى األنواع (‪ C ،D‬و ‪.)B‬‬
‫أظهر ألبحث كفاءة استخدام برنامج ‪ PLAXIS 3D 2013‬في تحليل ألركائز ألنواع مختلفة من‬
‫التربة تحت تأثير الزالزل‪.‬‬
‫الحد األقصى لعزم االنحناء أثناء الزلزال يحدث في منطقة التقاء طبقات التربة المختلفة على طول‬
‫عمق الركيزة لكل نماذج التربة‪ .‬كذلك ‪ ،‬فأن أعلى وأدنى ازاحة األفقية تحدث في قمة الركيزة وسطح األرض‬
‫على التوالي‪ .‬وتبين أن سرعة موجة القص واالجهادات تلعب دورا هاما في تقدير السلوك الديناميكي للركائز‪.‬‬
‫اظهرت نتائج الدراسة أنه عند زيادة طول الركيزة )‪ ، (Lp‬يزداد االنحراف األفقي ودرجة االنحناء‬
‫بسبب زيادة نسبة ‪ Lp/Dp‬حيث ان ‪ Dp‬هو قطر الركيزة‪ .‬وعند ارتفاع نسبة ‪ Lp/Dp‬أعلى من ‪ 22‬يزداد‬
‫الهطول العمودي لرأس الركيزة ليصل الى عشر اضعاف عندما يصل طول الركيزة الى الضعف‪ .‬كذلك‪ ،‬هناك‬
‫زيادة في مقدار العزم و تناقص في انحناء االنحراف االفقي مع زيادة قطر الركيزة‪ .‬مع العلم بان الحد األقصى‬
‫لعزم االنحناء لركيزة بقطر ‪2.3‬م أقل بنسبة ‪ ٪62‬من ركيزة بقطر ‪1‬م ‪ ،‬في حين‪ ،‬يمكن خفض الهطول‬
‫العمودي لرأس الركيزة الناجمة عن الزلزال بنحو ‪ ٪32‬مع زيادة قطر الركيزة من ‪ 2.3‬م إلى ‪ 1‬م‪.‬‬
‫وأخيرا‪ ،‬فقد لوحظ زيادة العزم االقصى بنحو ‪ ٪12‬مع زيادة معامل المرونة لمادة الركيزة بنحو‬
‫‪ .٪12‬وأشارت النتائج إلى أن نظام التربة‪-‬ركيزة ال يمكنها أن تتحمل زلزاال قوته (‪ )ML‬تقريبا ً مساوية أو‬
‫أعلى من ‪ 3.3‬في المنطقة الوسطى من العراق‪.‬‬
‫السلوك الزلزالي لنظام تربة‪-‬ركيزة‬
‫رسالة‬
‫مقـدمة إلى كليـة الهندسـة في جامعـة النهرين و هي جـزء من متطلبات نيل درجة‬
‫ماجستيرعلوم في الهندسـة المدنية‬
‫من قبل‬
‫ربى حنا مجيد ساعور‬
‫(بكالوريوس‪)7991 ,‬‬
‫‪7411‬‬ ‫شعبان‬
‫‪6172‬‬ ‫آيار‬

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SEISMIC BEHAVIOR OF A SOIL-PILE SYSTEM

Ruba Hanna Majeed Sa'ur

Capter Two: Literature Review

3.4.2.4 Unconsolidated-Undrained Triaxial Compression Test (UU Test) 45

3.4.2.5 Consolidated Undrained Triaxial Compression Test (CU Test) 46

Chapter Four: Finite Element Dynamic Modeling and verification Problems

Chapter Five: Parametric Study

5.3 Influence of Soil Dynamic Parameters on the Behavior of Pile 91

Chapter Six: Conclusions and Recommendations

[C] Damping matrix.

Table Title Page

1.2 Problem Statement

principle of superposition can be used to superimpose loading at different frequencies.

1.3 Scope of the Study

1.4 Thesis Layout

Figure (2.1) Seismograph instrument.

2.2.2 Seismic Waves

2.2.2.1 Body Waves

2.2.2.1.1 P wave (body wave)

Figure (2.2) Primary wave (after Jasim, 2010).

2.2.2.1.2 S wave (body wave)

Vp/Vs = [(1- υ)/1+ υ)] ½ (2.4)

Figure (2.3) Secondary wave (after Jasim, 2010).

2.2.2.2 Surface Waves

2.2.2.2.1 Love wave (surface wave)

Figure (2.4) Love wave (after Jasim, 2010).

2.2.2.2.2 Rayleigh wave (surface wave)

Figure (2.5) Rayleigh wave (after Jasim, 2010).

2.2.3 Methods for Determining Dynamic Properties of Soil

Figure (2.6) Classification of dynamic methods for obtaining shear modulus(after

Figure (2.7) Flowchart of dynamic parameters used in foundation design.

2.2.4 Measurement Scales of Earthquakes

2.2.4.1 Magnitude of an Earthquake

2.2.4.2 Intensity of an Earthquake

2.3 History of Earthquake Studies in Iraq

Al-Heety (2010) analyzed the seismicity of Iraqi western desert as shown in

* Estimated data from interviews.

2.4 Effect of Earthquake

earthquakes. These may occur either alone or in combinations to add to

2.5 Soil-Structure Interaction

use numerical methods for analyzing soil-pile-structure interaction problems (Ahmadi

2.6 Kinematic Bending Moment

Where amax,s is the maximum acceleration at surface based on seismic zonation;

While r is the pile diameter; γ1 is the strain of the upper layer; Q is an

Figure (2.12) Comparison between bending moments predicted by analytical

Figure (2.13) Experimental and theoretical results of maximum kinematic bending

2.7 Piles behavior under earthquake action

Miyamoto Y. (2000) studied the pile foundation response during earthquakes

Muthukkumaran and Subha (2010) studied the performance of piles in

Figure (2.19) Pile failure mechanisms (after Meyersohn, 1994).

Figure (2.20) (a) Prototype 15-story building supported by end-bearing pile

3.2 Resource of Data and Presentation

2 Kirkuk Kirkuk Cement Factory N2

6 Baghdad Eiwa'n Al Madain M3

10 Karbala Karbala Cultural WS1

12 Al Najaf Al Najaf Al Salam Housing Complex WS3

13 Missan Al Amarah Water Intake Depot ES1

18 Al Nasiriya Al Nasiriya Water Intake Refinery S3