Well Pile Foundation PDF
Well Pile Foundation PDF
Well Pile Foundation PDF
GOVERNMENT OF INDIA
MINISTRY OF RAILWAYS
(Railway Board)
ADOPTED 1941
REVISED EDITION - 1985
ISSUED BY
RESEARCH DESIGNS AND STANDARDS ORGANISATION
LUCKNOW - 226011
IIB-i
INTRODUCTION
This manual covers the design and construction of well foundation and pile foundations for
Railway bridges, which generally form part of the permanent foundations for long span bridges.
These foundations are commonly used for transferring heavy loads to deep strata in river bed
from piers and abutments of bridges.
This manual finalised by RDSO has been approved by the Bridge & structure Standards
Committee. The Chief Engineers may issue supplementary instructions from time to time to suit
local working conditions.
IIB-ii
CONTENTS
PAGE NO
1. WELL FOUNDATIONS
1.1
Depth of foundation.
1.2
1.3
Loading.
1.5
1.6
Cutting edges.
1.7
Well curb.
1.8
Well steining.
1.9
Bottom Plug.
1.10
Top Plug.
1.11
Well cap.
1.12
2. PILE FOUNDATIONS
2.1
Classification of piles.
2.2
Types of piles.
2.3
Spacing of piles.
2.4
2.5
2.6
Pile grouping.
10
2.7
11
2.8
Load test.
11
2.9
11
IIB-iii
(a)
The dredge hole should be large
enough to permit dredging.
(b)
The steining thickness should be
sufficient to enable sinking without
excessive kentledge and provide adequate
strength against forces acting on the
steining, both during sinking and service.
The well steining should also be designed
to withstand the earth pressures acting only
on two opposite sides or only on
diametrically opposite quadrants under
conditions of sand blowing. The effect of
heap of earth dumped near the well during
sinking shall also be taken into account.
(c)
It should accommodate the base of
the substructure and not cause undue
obstruction to the flow of water.
(d)
The overall size should be sufficient
to transmit the loads safely to the soil
without exceeding its allowable bearing
pressure.
IIB-iv1
2C K a
tan 2 in
F = 9.8 K a Z
N/m2
F = K a Z
2C
2
K a
tan in kg / m 2
3
Where,
F = Skin friction in N/m2 (kg/m2)
Ka = Active earth pressure coefficient.
IIB-2
C =
strength.
= Angle of shearing resistance of soil.
Soil
Value of
skin
friction
KN/m2
Value of
skin
friction
Kg/m2
7.16 to
28.73
47.86 to
191.52
11.96 to
33.54
33.54 to
67.08
47.86 to
95.71
730 to
2930
4880 to
19530
1220 to
3420
3420 to
6840
4880 to
9760
Loading
IIB-3
1.8
Well Steining Well steining shall
be built of masonry or cement concrete
not weaker than M-100 grade. Sufficient
bond rods shall be provided to bond the
units of the steining during the progress of
construction.
Bond rods shall be
distributed evenly on both faces of
steining and tied up by providing adequate
horizontal hoop reinforcement.
For
masonry steining and for concrete steining
of small thickness, bond rods may be
provided in one row in the centre only and
tied up by providing plates or hoop
reinforcement.
1.9
Bottom Plug A bottom plug shall
be provided for all wells and its top shall
be kept 300 mm above the top edge of the
inclined face of the curb. The concrete
used for the bottom plug when placed
under dry conditions shall generally be of
1:3:6 proportions and it shall be placed
gently in one operation. When the
concrete is placed under water, the
quantity of cement shall be increased by
10% and it shall be placed by tremie or
skip boxes under still water condition.
1.10 Top Plug A 300 mm thick plug of
cement concrete 1:3:6 shall be provided
over the hearting which shall normally be
done with sand. Sometimes only water is
filled to reduce the weight.
1.11 Well Cap The bottom of the well
cap shall, as far as possible, be located
300 mm above low water level. All the
longitudinal bars from the well steining
shall be anchored into the well cap. The
well cap shall be designed as a slab
resting on the well.
1.12
Pneumatic Sinking Of Wells
Where boring data indicate pneumatic
sinking, it will be necessary to decide the
method of such sinking and location of air
lock.
1.12.1. The side wall and roof of the
working chamber shall be designed to
withstand the maximum air pressure
envisaged with the use of pneumatic
sinking equipment.
The design air
pressure for design shall be higher than
(i)
Extra hoop reinforcement, if
required to be provided, shall overlap at
least one bond length below the section
from where MS plates are provided for
protection against blasting or other
reason.
(ii)
The pneumatic platform and the
weight of the steining and kent ledge, if
any, shall be sufficient to resist the uplift of
air from inside.
(iii)
If at any section of steining the
uplift pressure is more than the total
weight acting downwards, then the
platform and the steining can be weighed
down by kentledge and also anchored to
the steining, if necessary.
(iv)
The well steining shall also be
checked at different sections for any
possible rupture against the uplift force
and upto the height at which the uplift
force is balanced by the self weight of the
steining and any superimposed load on it.
2. PILE FOUNDATIONS
2.1 Piles may be divided into the following
categories depending upon the manner of
transference of load:
(i)
Friction Piles
(ii)
Bearing Piles
(iii)
Bearing-cum-friction piles
2.1.1. Friction Piles: These piles transfer
the load primarily by skin friction
developed along their surface.
2.1.2. Bearing Piles: These piles transfer
the load primarily by bearing resistance
developed at the toe.
IIB-4
2.2.
Piles may also be further divided
into the following categories, depending
upon the method of construction.
(i)
Pre-cast driven piles.
(ii)
In-situ driven piles (these are
normally not used for Railway Bridges).
(iii)
In-situ bored piles (only large
diameter bored piles are normally used for
Railway Bridge construction.)
2.2.1. Selection of type of pile.
The type of pile shall be selected by
considering broadly the following factors:
(i)
Availability of space. Driven piles
require large areas and head room since it
needs larger and heavier driving rigs.
Bored
piles,
however,
require
comparatively smaller space.
(ii)
Proximity to structure:
Driving causes vibration of the ground
which may damage nearby structures.
(iii)
Reliability:
Precast driven piles ensure good quality of
material, uniform section of piles and give
a valuable guide to the load carrying
capacity. In cast-in-situ piles, segregation
of concrete is possible in water-logged
areas.
(iv)
Compaction of cohesion-less soil
is effected if driven piles are used.
(v)
Cast-in-situ piles can be formed to
any desired length and no cutting of pile or
addition in length is required.
2.3.
Spacing of Piles
2.4.1.
(a)
The ultimate bearing capacity of a
pile may be assessed by means
of a
dynamic pile formula, using data obtained
during driving of piles or by a static
formula on the basis of soil-test results or
by a load test.
(b)
For non-cohesive soils, Hileys
formula is more reliable than other
formulae.
This formula is given in
Appendix `E of IS: 2911(Part-I)-1969.
(c)
Hileys formula is not reliable in
cohesive soils.
(d)
The static formula should be used
with careful judgment as the mechanics of
load transfer from pile to soil is very
complex. This judgment is employed in
selecting appropriate multiplying factors.
(e)
In unknown areas, load test is
therefore most desirable.
(f)
Where scour is anticipated,
resistance due to skin friction will be
available only below the scour line and
this must be taken into account, in all the
three methods.
2.4.2. When piles are installed through
compressible fill or sensitive clay into
underlying hard stratum, a drag down
force is generated in the fill or the clay
stratum. This must be added to the load.
IIB-5
Piles in non-cohesive
Soil:
The ultimate bearing capacity Qu of a pile
in homogenous sand may be represented
by
Qu = Qp+ Qs Where Qp = Point resistance
Qs = Skin resistance
= qp Ap + fs As where q p = po Nq
1000
16
12
8
4
qL
100
Nc
20
with
Nq
10
10
8
6
4
Dc
B
1
0
10
20
30
40
Fig.2
Bearing Capacity Factors and
Critical Depth Ratios For Driven Piles.
Critical depth ratios (Dc/B) for various
values and Nc, Nq factors; at different
values for different Db /B values in q case
of driven piles. The average ultimate unit
skin friction, fs in homogenous sand may
be expressed by
fs=ks po tan f1 In which
ks= the average coefficient of earth
pressure on pile shaft,
IIB-6
H = Driven H Piles
= Bored piles
1
H
30
35
40
1.4
1.2
Unit skin friction fs in Tons/Sq.ft.
O = Bored piles
1.0
0.8
H
0.6
0.4
0.2
0
30
35
40
qc x Db
qp = ----------10B
qL
IIB-7
Qu
Db=9m
Deepest
Scour Level
SANDY
STRATA
Toe of Pile
A3 Db/B
Dc/B, the condition for limiting
value of q1 is satisfied.
Using Db/ B-Nq curves of Fig 4.
We get Nq = 22 for = 25
Therefore, qL = 0.5 x Nqx tan
= 0.5 x 22 x tan
= 5.1 t/sq.m
Effective over-burden pressure = p0
= Submerged density of soil x bearing
depth= 0.8 x 9 = 7.2 t/sq.m
qp= p0 x Nq
= 7.2 x 22 = 158.2 t/sq.m
since
qp qL
Therefore, q1 is adopted for calculating the
unit point resistance i.e. qp will be taken as
5.lt/sq.m
Therefore, the ultimate point resistance
Qp= qp x Ap
= 5.1 x /4 x (1.20)2
= 5.7 tonnes
(B) Friction resistance
From the formula, the limiting value of unit
skin friction
f1 = .22 N
IIB-8
80 70 60 50 40 30 20 10
Therefore, = 41 45
fs = KspoTan = 0.75 x 3.6 x tan 41 45
=2.410t/sq.m
2.5 Factor
Foundation
28
30
32
34
36
38
40
42
44
46
Fig 4 A
Of
Safety
For
Pile
IIB-9
Pile Grouping
2.6.1.
The bearing capacity of a pile
group may be worked out as under:
Bearing
Type of
Strata
capacity
of
Pile
the Pile group
No. of piles x
1. Dense sand
SPC *
not underlain
Driven
by weak
deposit.
(Nos. of
piles x SPC)
2. Loose
sandy soil
3. Sand not
underlain by
weak deposit
Bored
2/3 (No of
piles x SPC)
IIB-10
2.9.1
The
lateral
load
due
to
tractive/braking effort is transferred to the
cap level along with a moment. The
bending moment transferred at the pile
cap level is shared by the piles in the
group.
2.9.2 The piles should be considered as
partially restrained at the pile cap level.
IIB-11
G.L.
D/3
G.L.
1
2
TOTAL LOAD
BEARING STRATUM
G.L.
1
SOFT SOIL
FRICTIONAL LOAD
2
TOTAL LOAD
H/3
BEARING STRATUM
(c)
12
FIG. 5- APPROXIMATE SOLUTION
IIB-12
IIB-13