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EXPANSIVE SOIL STABILIZATION-GENERAL CONSIDERATIONS

Conference Paper · June 2017

DOI: 10.5593/sgem2017/32/S13.033

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 Section Exploration and Mining

EXPANSIVE SOIL STABILIZATION - GENERAL CONSIDERATIONS

PhD Students.Larisa CHINDRIS1,, Ph.D.1,Prof. Dan Paul STEFANESCUU

Ph.D.2,Lecturer Ladislau RADERMACHER Ph.D.1, PhD Students eng.Cristian
RADEANU1, PhD Students eng.Cristian POPA1.
1
University of Petroşani, Romania
2
University Lucian Blaga Sibiu Romania

ABSTRACT:

It is a well-known fact that a construction is as strong as its foundations are.

Nowadays the constructions sites with good soils for foundations are fewer and fewer.
One of the most encountered issue on sites, especially in road construction is the
presence of highly cohesive soils, soils that are easily affected by the change of the
water content. Active clay soils present a problematic challenge for civil and
geotechnical engineers all over the world. Key aspects that need identification when
dealing with expansive soils include: soil properties, suction/water conditions, water
content variations temporal and spatial, (generated by trees and the seasonal change),
and the geometry/stiffness of foundations and associated structures built on active
shrink/swell soils. Stabilization procedures are available in order to reduce or
completely eliminate the swelling potential of expansive clays. The problematic soil is
removed and replaced by a good quality material or treated using mechanical and/or
chemical stabilization. Different procedures can be used to improve the geotechnical
characteristics of problematic soils by treating in situ. One of the preferred solutions for
soil stabilization is treatment with mineral binders. The solution has been proven to be
effective of various types of cohesive soils.

Keywords: Soil stabilization, clay soils, expansive soils, lime, hydraulic binders,
bearing capacity, improvement, and treatment

INTRODUCTION

Active clay soils present a problematic challenge for civil and geotechnical
engineers all over the world. Costs associated with the phenomena of swelling and
shrinkage of active clay soils run into several millions of euros annually. Key aspects
that need identification when dealing with expansive soils include: soil properties,
suction/water conditions, water content variations temporal and spatial, (generated by
trees and the seasonal change), and the geometry/stiffness of foundations and associated
structures built on active shrink/swell soils. [13]
The current paper reviews the phenomena of active clays from a mineralogical,
mechanical and especially a geotechnical point of view.
Clay soils exhibit, sometimes, a significant volume change due to the variation
of water content in the mass of the soil, in response to climatic conditions and the action
of vegetation.
These volume changes affect the function of the constructions and foundations
in contact with the soil and they represent the causes of damage, especially intense,
during periods of drought. [4]
17th International Multidisciplinary Scientific GeoConference SGEM 2017

Some first indicators of the presence of expansive soils are:

• Foundation cracks
• Heaving and cracking of floor slabs and walls
• Jammed doors and windows
• Ruptured pipelines
• Heaving and cracking of sidewalks and roads
To better understand these phenomena, it is considered appropriate to analyze
separately the following six main points of view when dealing with active clay soils:
• The identification of soil and terrain structures most sensitive to water content
variations and forecasting the amplitude of their deformations, thus their
retraction or swelling.
• Analysis of the effect of volume changes of clay soils on the movement of
foundations and construction deformations.
• The study of foundation solutions and reinforcement of structures that can
directly limit the effects of the expansion and contraction of clay soils.
• Analysis of changes in the hydric profile in response to stress conditions, taking
into account the influence of vegetation and soil-atmosphere interface.
• Study and development of solutions to limit the variations of water content in
soils under the buildings and in the nearby soil.
• The elaboration of recommendations that take into account all these phenomena
and the methods to control their effects. [10]

GENERAL ISSUES - DEFINITION AND GENERAL PROPERTIES OF CLAYS

AND CLAY MINERALS

The definition of clay is diverse. Variations exist among different fields even
though fundamentally there is much in common among the visualized materials. The
definitions so far used may be grouped into three kinds as follows (summary from Sudo
et. al, 1981) [11]
Clay comes predominantly by alteration of rocks and it is in perpetual evolution
on a geological time scale, passing from one to another clay mineral (from smectite to
illite, for example) and changing its initial properties depending on the environmental
factors.
Clays have been defined on the basis of an assembly of certain specific
characters such as plasticity, small particle size, hardening on firing, and chemical
constitution (i.e. as consisting largely of silica, alumina and water). This definition is
applied in a broad sense.
The definition of clays that has been given in terms of the relative proportion of
the clay fraction in rocks or soils (Clay-area designated on the triangular diagram with
the component proportions of sand and silt) to the fractions of sand and silt is, however,
inconsistent from Sudo et. al point of view.
The most important grain property of fine-grained soils is the mineralogical
composition. If the soils particles are smaller than 0.002mm, the influence of the
gravitational force on the particles is insignificant compared to the electrical force
acting on the surface of the particle. (Terzaghi et al.) [14]
All the clay minerals are crystalline hydrous aluminosilicates having a lattice
structure, similar to the pages of a book, in which the atoms are arranged in several
layers. The colloidal particles of soil consist primarily of clay minerals that were
 Section Exploration and Mining

derived from rock minerals by erosion, but that have differing mineralogical structure
from those of the initial minerals. [12]
Three important structural groups of clay minerals are described for engineering
purposes as follows:
• Kaolinite group – generally non-expansive
• Mica-like group – includes illites,vermiculites and chlorites, which can be
expansive, but generally do not pose significant problems.
• Smectite group – includes montmorillonites, which are highly expansive and are
the most troublesome clay minerals. (Nelson et al. 1992) [6]

WATER AND CLAY SOIL INTERACTION

It is well known that if the moisture content of the clay remains the same, its
volume won’t change, hence the structures built on clays with constant moisture content
will not be subjected to heave stress.
Compared to the typical three-phase (solid particle, water and air) structure of
the general soil groups, clay soil has a thin layer of water bounded to its clay mineral
surfaces.
The bound water is comprised of water molecules that are oriented due to the
charged mineral surface. These molecules cannot rotate as freely as the bulk pore water
under alternating electric field, resulting in less polarization compared with that of “free
water”, and a lower measured dielectric constant. The volume fraction of bound water is
determined by the soil specific surface and soil dry density (Stanciu 2006) [1].

CLAY PROPERTIES- CATION EXCHANGE CAPACITY

Clay contributes many benefits to the physical, chemical and biological

properties of soil. It increases the soil’s cation exchange capacity, enhances water-
holding capacity, provides elasticity, and acts as a binding agent for the non-clay
components. (Tucker, 1999) [7]
Cations that neutralize the net negative charge on the surface of soil particles in
water are readily exchangeable with other cations. The exchange reaction depends
mainly on the relative concentrations of cations in the water and also on the
electrovalence of the cations. Cation exchange capacity, measured in milliequivalents of
cations per gram of soil particles, is a measure of the net negative charge on the soil
particles, resulting from isomorphous substitution and broken bonds at the boundaries.

Figure 1 Cation Exchange in a Na+ rich clay (After I. Manoliu, 2010)

Cation exchange capacity of clays is the fundament of chemical stabilization
practice of clayey soils (Manoliu) [8].
Cation exchange capacity, that is, ability to exchange of ionic species is
probably the most important physico-chemical characteristic of smectite-rich rocks.
17th International Multidisciplinary Scientific GeoConference SGEM 2017

This property is linked to their chemical activity and common cation substitutions. The
ions or molecular species are attracted by a charged surface of clay particles (process of
adsorption) or to the internal surface of clay particles (process of absorption) (Velde,
1995).

PHYSICAL SOIL PROPERTIES

Clay mineralogy is one of the properties that influence the volume change in
clay soils. Montmorillonites, Vermiculites and some mixed layer minerals typically give
shrink-swell potential to clayey soils, in opposition to Illites and Kaolinites that are
infrequently expansive, though, they can cause volume changes when particle sizes are
extremely fine (less than a few tenths of a micron). (Mitchell, 1976) [15]
Soil water chemistry – swelling is repressed by increased cation concentration
and increased cation valence. Mg2+ cations in the soil water would result in less
swelling than Na+ cations. (Mitchell, 1976) [15]
Soil suction – Soil suction is an independent effective stress variable, repressed
by the negative pore pressure in unsaturated soils. Soil suction is related to saturation,
gravity, pore size and shape, surface tension and electrical and chemical characteristics
of the soil particles and water. (Miller, 1992) [6]
Plasticity – In general, soils that exhibit plastic behavior over wide ranges of
moisture content and that have high liquid limits have greater potential for swelling and
shrinking. Plasticity is an indicator of swell potential.
Soil structure – Flocculated clays tend to be more expansive than dispersed
clays. Cemented particles reduce swell.
Dry density – Higher densities usually indicate closer particle spacing, which
may mean greater repulsive forces between particles and larger swelling potential.
(Chen, 1975) [2]
Initial moisture condition – A desiccated expansive soil will have a higher
affinity for water, or higher suction, than the same soil at higher water content, lower
suction. Conversely, a wet soil profile will lose water more easily on exposure to drying
conditions, and shrink more than an initially dry profile.
Moisture variations – Changes in moisture in the active zone near the upper part
of the profile primarily define heave. It is in those layers that the widest variation in
moisture and volume change will occur. (Miller, 1992) [6]
Stress history – an over consolidated soil is more expansive than the same soil at
the same void ratio but normally consolidated. Swell pressure can increase on aging of
compacted clays, but amount of swell under light loading has been shown to be
unaffected by aging. Repeated wetting and drying tend to reduce swell in laboratory
samples, but after a certain number of wetting – drying cycles, swell is unaffected.
(Mitchell, 1976) [15]

TREATMENT OF EXPANSIVE SOILS

Treatment procedures are available in order to reduce or completely eliminate

the swelling potential of expansive clays. The problematic soil is removed and replaced
by a good quality material or treated using mechanical and/or chemical stabilization.
Different procedures can be used to improve the geotechnical characteristics of
problematic soils by treating in situ.
 Section Exploration and Mining

• These procedures are:

• Prewetting
• Moisture control
• Chemical stabilization
• Compaction control
• Soil Replacement
• The use of reinforcing elements (such as geotextiles and stone columns)
Preliminary soil investigation must be undertaken before choosing the
appropriate type of soil treatment. The successful application of soil treatment
procedures requires considerable experience and judgment regarding the soils in-situ,
method of procedure application and limitations of procedures. The procedures require a
specific methodology for every situation.
Prewetting is an old concept among civil engineers. Chen, 1975 [2] and Nelson
and Miller, 1992 [6] describe the procedure correlating it to the theory that moisture can
migrate from a moderate depth water table to an upper moisture-deficient soil my means
of capillary rise or by means of thermo-osmosis, from a high-temperature area to a low-
temperature area. The procedure is being based on the theory that increasing the
moisture content in the expansive foundation will cause swelling to occur prior to
construction and if the high soil moisture content is maintained, the soil volume will
remain essentially constant, achieving a no-heave state and therefore structural damage
will not occur. There are great limitations regarding this procedure, being that expansive
soils generally exhibit low hydraulic conductivity, therefore the time required for
adequate wetting can be up to several years. Another major limitation to this procedure
is that after a long period of time applying water to the soil, it can conduct to serious
loss of soil strength and can cause a reduction in bearing capacity and soil stability.
Chen, 1975 quoted E. J. Felt (1966) [2] regarding a prewetting project in which the soil
moisture content did not increase appreciably after the first month of prewetting. For 5
months thereafter, soil swelling continued. It was suggested that the first infiltration of
water was probably taken by seams and fissures present in the clay and, therefore, full
soil expansion did not occur. As time passed, the water moved from the fissures into the
blocky soil mass, and swelling took place throughout the mass of the soil and not
merely a seepage path.
This method may be best suited for soils with low or moderate expansion
potential. Therefore a good assessment of the expansion potential should be undertaken.
Soil replacement is considered to be an easy solution for resolving the issue of
problematic foundation soils. The procedure consists in replacing the expansive soil
with non-swelling soils, this being the first requirement, followed by details concerning
type of material, depth of replacement and extent of replacement. For man-made fill the
extent of the layer should be limited. The depth of replacement is determined based on
the swelling characteristics of the soil determined by laboratory testing, uplift pressure
and the actual heave in the field. The cost of soil replacing is comparatively smaller to
other techniques, like chemically treatments.
Compaction and moisture control refer basically to the determination of the
optimum density of the soil and apply the compaction with 4-5% higher than the
optimum in the field. It is a very difficult operation. Moisture content is the most
important factor in the calculations but the process of re-compacting swelling clays at
moisture contents slightly above their natural moisture content and at a low density
should be the preferred approach. The main advantage of the technique is that it
17th International Multidisciplinary Scientific GeoConference SGEM 2017

increases the strength of the soil, reduces swelling potential without adverse effects.
With modern construction techniques, it is possible to scarify, pulverize, and recompact
the natural soil effectively without substantially increasing the construction cost.
Subgrade stabilization is one of the most common uses of geotextiles. The
process requires extent knowledge of the characteristics of the geotextiles, thus they
must have specific mechanical and hydraulic properties in order to perform properly.
Stone columns are extensively used to improve the bearing capacity of low grade soils.
A stone column is one of the soil stabilization methods that is used to increase strength,
decrease the compressibility of soft and loose fine graded soils, accelerate a
consolidation effect. They are mainly used for stabilization soft soil such as soft clays,
silts and silty-sands. It is believed that this method was used first in France in 1830s.
The columns consist of compacted gravel or crushed stone arranged by a vibrator.
Chemical stabilization practice includes the use of lime and/or other chemicals,
both organic and inorganic to stabilize expansive soils. These products can be cement,
fly ash, and combinations between them in different percentages depending on the
stabilized soil desired characteristics. Other chemicals are sodium or calcium based
compounds (calcium hydroxide, sodium chloride etc) (Chen, 2003) [3]. In general soil
stabilization is a practice used in the field of highway construction and road pavements,
but has been used successfully in the stabilization of the subgrade soil for individual
buildings.
Hydraulic binders:
• Portland Cement
• Lime (Hydrated Lime, Quicklime, Slurry)
• Fly Ash
• Pozzolanic materials
Organic binders:
• Tars
• Bitumen
• Organic resin
• Polymers

CHEMICAL STABILIZATION PRACTICE - LIME STABILIZATION

Lime stabilization has been used successfully on many projects to minimize

swelling and improve soil plasticity and workability. Lime improves the strength of clay
by three mechanisms: hydration of quicklime, flocculation, and cementation. The
theoretical chemistry behind lime stabilization of clayey soils is complex. [5]
The first and second mechanisms occur almost immediately upon introducing
the lime in the soil, while the third is a prolonged effect. One of the most important
factors that define the soil/lime reactivity is the pH. Therefore a soil pH greater than 7
indicates usually a good reactivity to lime treatment. Organic carbon reduces lime-soil
reactions. Also, poorly drained soils tend to have a better reaction to lime treatment than
well-drained soils. Calcareous soils have good reactivity. Depending of the depth of the
problematic soil and the type of geotechnical application, two types of chemical
stabilization can be defined: surface and deep stabilization.
In general, smaller amounts of additives are required when it is desired only to
modify the soil properties such as workability and plasticity. When it is needed to
improve the strength and durability significantly, larger quantities of additives are used.
 Section Exploration and Mining

The National Lime Association in the USA gives a general context about lime treatment
procedure. Lime in the form of quicklime (calcium oxide – CaO), hydrated lime
(calcium hydroxide – Ca[OH]2), or lime slurry can be used to treat soils. Quicklime is
manufactured by chemically transforming calcium carbonate (limestone – CaCO3) into
calcium oxide. Hydrated lime is created when quicklime chemically reacts with water.

It is hydrated lime that reacts with clay particles and permanently transforms
them into a strong cementitious matrix. (LIME, 2004) [9]
Hydrated lime is the most used in chemical stabilization application, whilst
quicklime stabilization represents only 10 percent of the lime used in stabilization
procedures.
Quicklime is more difficult to use in day to day practice due to its corrosive
properties, increased security measures are required, although in some cases it has been
proven to be more effective than hydrated lime. Quicklime can be effectively used for
the procedure of drying of the soil, due to its strong exothermic reaction in the presence
of water.
Most lime used for soil treatment is “high calcium” lime, which contains no
more than 5 percent magnesium oxide or hydroxide. On some occasions, however,
"dolomitic" lime is used. Dolomitic lime contains 35 to 46 percent magnesium oxide or
hydroxide. Dolomitic lime can perform well in soil stabilization, although the
magnesium fraction reacts more slowly than the calcium fraction.
Nelson and Miller [6] recommend a percentage of 3 to 8% of the weight of the
soil mass of hydrated lime to be added to the top several centimeters of the soil. Ismaiel
(2006) recommends a percentage between 3-5%, American Association of State
Highway and Transportation Officials (AASHTO) percentages of 2, 4 and 6%. Thus,
we conclude that the percentage of lime depends on the properties of the treated soil, the
final destination of the site and therefore the desired change in geotechnical parameters
of the treated soil compound.
The improvement of the geotechnical characteristics of clay soils by lime
stabilization occur in two general steps, from a chemical point of view. On a short term
reaction cation exchange and flocculation are included. Lime interacts with the clay by a
strong alkaline reaction, causing a base exchange, where calcium ions displace the
potassium, sodium and hydrogen cations. This causes a decrease in plasticity of the clay
soils by the appearance of flocculation and aggregation.
On a long term basis the pozzolanic reaction is defined by the appearance of the
silicate rich hydrates groups by the interaction of the calcium from the lime or
quicklime with the clay minerals.
Advantages and disadvantages of different types of lime include: for the dry
quicklime, the first advantage is the economical one. Being more concentrated a smaller
quantity is required in practice. The National Lime Association defines the report of dry
quicklime to dry hydrated lime to be ¾. [9] Disadvantages include special precaution
measures and special attention to ensure adequate water conditions, mellowing and
mixing. On the other side, for the dry hydrated lime, the advantages is that it can be
applied more rapidly than slurry lime, and that it can also dry the soil, but not as
effectively as quicklime. The major disadvantage of hydrated lime stabilization in
practice is the environmental factor. The hydrated lime consist in very fine particles,
 17th International Multidisciplinary Scientific GeoConference SGEM 2017

dust can be a problem and renders this type of application in dense populate areas
almost impossible.
The effectiveness of the lime treatment on clay soils is time dependent.
The outcomes of lime stabilization of the soil include:
• Dewatering of the soil as a reaction with Quicklime.
• Decreasing the plasticity index (Ip) and Augmentation of the plasticity limit
(Wp)
• Flocculation – change in grainsize distribution
• Reduction of the maximal Proctor density - Flattening of the Proctor Curve
• Augmentation of the CBR

CONCLUSIONS
We conclude that in general, all lime treated fine-grained soils exhibit decreased
plasticity, improve workability and reduced volume change characteristics. We need to
take into consideration that final aim improving also the strength characteristics of the
soil. It should be emphasized that the properties of soil-lime mixtures are dependent on
many factors such as soil type, lime type, lime percentage and curing conditions.

REFERENCES
[1] A. Stanciu and I. Lungu., Fundatii – Fizica si Mecanica Pamanturilor,
Editura Tehnica, Bucuresti, 2006;
[2] Chen, F. H., Foundations on expansive soils, No. Report Number 12
Monograph, 1975.
[3] Chen, W. F., & Liew, J. R. (Eds.), The civil engineering handbook, pp. 51-1.
Boca Raton: CRC Press, 2003;
[4] Felt, E. J. Influence of Soil Volume Change and Vegetation on Highway
Engineering, Highway Conference of the University of Colorado, 1953, January.
[5] Ismaiel, H. A. H., Treatment and improvement of the geotechnical properties
of different soft fine-grained soils using chemical stabilization, Shaker, 2006;
[6] John D. Nelson, Debora J. Miller, Expansive Soils – Problems and Practice
in Foundation And Pavement Engineering, Department of Civil Engineering Colorado
State University, 1992;
[7] M. Ray Tucker, Clay Minerals: Their Importance and Function in Soils,
1999;
[8] Manoliu I. and Radulescu N., Geotehnica I, Conspress (U.T.C.B.) Bucuresti,
Romania, 2010;
[9] National Lime Association, Lime-Treated Soil Construction Manual - Lime
Stabilization & Lime Modification, Bulletin 326, 2004;
[10] NORMATIV NP 126-2012 “Fundarea Constructiilor pe Pamanturi cu
Uumflari si Contractii Mari.”, INCERC Romania;
[11] Sudo T., Shimoda S., Yotsumoto H., Aita S., Electron Micrographs of Clay
Minerals, 1981;
[12] Velde B., ed., Origin and Mineralogy of Clays, 1995;
[13] Chindris L.C. Analiza fenomenului de contracție-umflare a pământurilor
argiloase: impactul pierderii umidității solului asupra clădirilor ușoare, 2013.
[14] Karl Terzaghi,Ralph B. Peck,Gholamreza - Soil Mechanics in Engineering
Practice
[15] Mitchell, J.K – Fundamentals of soil Behaviour, 1976 – New York

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