CHEMICAL STABILIZATION OF EXPANSIVE SOILS USING LIQUID IONIC
SOIL STABILIZERS (LISS)
by
Shi He
Presented to the Faculty of the Graduate School of
The University of Texas at Arlington
in Partial Fulfillment of the Requirements
for the Degree of
DOCTOR OF PHILOSOPHY
THE UNIVERSITY OF TEXAS AT ARLINGTON
Aug 2019
i
Copyright © by Shi He 2019
All Rights Reserved
ii
This work is dedicated to my grandfather, who took care of me in my
childhood and to my beloved parents.
iii
ACKNOWLEDGEMENTS
First, I would like to express my deepest gratitude to my research advisor,
Dr. Anand J Puppala for offering me the opportunity to pursue my doctoral research
under his excellent guidance. In addition, his enthusiasm attitudes in the field of
geotechnical always inspire and encourage me. Furthermore, I also appreciate him
for providing me with fantastic research facilities and a very environmental-
friendly study space.
I would also like to convey my gratitude to Co-advisor Dr. Xinbao Yu for
his suggestions and professional guidance. Furthermore, I am also obliged to Dr.
Jiechao Jiang and Dr. Shih-Ho (Simon) Chao for accepting to be my committee
members. I would like to gratitude them for their valuable advice and insightful
comments. Apart from that, I would appreciate Dr. Sayantan Chakraborty to
retouch my dissertation and papers.
Moreover, I would appreciate all the members of Department of Civil
Engineering staff, Mr. Paul Shover, Ms. Sarah and Ms. Ava Chapman for their
unconditional support during my course study in UTA. This research was funded
by NSF Industry-University Cooperative Research Center (I/UCRC) program
funded ‘Center for Integration of Composites into Infrastructure (CICI)’ site at
UTA (NSF PD: Dr. Andre Marshall; Award # 1464489). Their financial support is
gratefully acknowledged. I would extend my sincere appreciations to Mr. Scott
Horn and Mr. Ben Baker from TX Prochemical Soil Stabilization, Inc for helping
iv
me with sampling the expansive soil for this research. I would also like to thank
Mr. David for training me to use different equipment in CCMB.
I would like to express my appreciation to my colleagues Dr. Aravind
Pedarla, Dr. Ujwalkumar Patil, Dr. Tejo Bheemasetti, Dr. Aritra Banerjee, Dr. Sarat
Congress, Dr. Raju Acharya, Dr. Alejandro Pino, Dr. Nan Zhang, Dr. Santiago, Dr.
Minh Hai, Dr. Jasaswee Das, Dr.Ali Shafikhani, Dr.Anu George, Leila, Xuelin,
Teng, Rakib, Gang, Omid,Tom, Puneet, Rinu, Manikanta, Nice, Ashraf, Nripojyoti,
Burak, Jose, Sandesh, Esmat, Jacque, Kaleisha, Shruti and Prince for their sincere
support and encouragement during this research work.
I would also like to thank my beloved parents and auntie for their continuous
support and encouragement. Finally, I would like to thank my grandparents who
took care of me during my childhood.
July 17, 2019
v
ABSTRACT
CHEMICAL STABILIZATION OF EXPANSIVE SOILS USING LIQUID
IONIC SOIL STABILIZERS (LISS)
Shi He
The University of Texas at Arlington, 2019
Supervising Professors: Dr. Anand J. Puppala and Dr. Xinbao Yu
Traditional soil stabilizers such as lime and cement are widely used to
reduce swell and shrinkage behavior and enhance strength properties of expansive
soils through the formation of cementitious products. However, the manufacturing
process of these calcium-based stabilizers, such as lime and cement, need large
amounts of water and emit gases such as CO, CO2, NOx, and SO2 that are harmful
to the environment. Hence, environmentally-friendly techniques are often sought
out by the civil infrastructure industry (Puppala et al. 2018a, 2019b, George et al.
2019a, Congress and Puppala 2019).
In this research, an alternative stabilizer termed as liquid ionic soil stabilizer
(LISS) was used to treat expansive soils from North Texas. Although LISS has
shown a reliable record of successful stabilization treatment of subgrades for over
20 years in Texas, there is a lack of in-depth studies which try to identify the
probable stabilization mechanisms and quantitatively evaluate the efficacy of such
treatments. This research work primarily aimed at addressing these issues through
an extensive laboratory testing program encompassing a series of macro-scale
engineering tests and microstructural analyses.
Two types of expansive soils with different clay mineral compositions were
collected from different locations in Texas and are used as control soils in the
vi
present laboratory testing program. These soils were modified by treating the soils
with three different dilution ratios of LISS additive. The dilution ratio is defined as
the volume of concentrated liquid ionic stabilizer per unit volume of water. The
research study included four major tasks to study the effects of LISS stabilization
and these are: (a) performing physical, chemical and microstructural tests, (b)
evaluating engineering properties, (c) assessing stabilization mechanisms, and (d)
numerical modeling to evaluate the post-treatment improvements in the
performance of slopes and pavement subgrades stabilized with LISS.
The collected soil samples were treated at three different dilution ratios to
study the effect of stabilizer dosage on the improvements in basic and engineering
properties of the problematic soil. Test results and analyses provided
comprehensive characterization of the basic and advanced soil properties,
improvements in engineering properties of treated soils, and an in-depth
understanding of the stabilization processes at a micro level. The mineralogical
and microanalysis studies were also performed to examine the stabilization
mechanisms in terms of chemical reactions, mineralogical changes, and other
modifications that might have resulted in improvements in the engineering
properties at the macro level.
The results from the macro tests that included physical, chemical, and
engineering tests showed that the LISS is an effective alternative environmental-
friendly soil stabilizer, which can enhance the strength and stiffness of problematic
expansive soils to moderate levels. The LISS also inhibits the swell potential of
expansive soils and slightly reduces the plasticity index and linear shrinkage ratio.
The reductions in swell potentials were associated with an increase in strength and
stiffness (resilient moduli) properties for all the different soil-dilution ratio
combinations used in this research study. Among the three dilution ratios used in
vii
this research, the double chemical ratio (10 ml/gallon) which had the highest
concentration of LISS exhibited the optimum performance based on the overall
improvements in engineering properties such as strength, stiffness, and reduction
in swell potential.
The probable stabilization mechanism was determined by comparing the
microstructural test results of Field Emission Scanning Electron Microscopy with
Energy Dispersive Spectroscopy (FESEM-EDS) and X-ray Powder Diffraction
(XRD) for both untreated and soils treated at the third ratio. Additional macro tests,
including variation in moisture content, pH, Consistency Limits and grain size
distribution with curing time, were also used to comprehend the changes in the
properties of the treated soil. The SEM images depicted that the soil particles
flocculated upon addition of LISS and a phospho-rich compound were formed that
bonded the soil particles after treatment. The intensity of the clay minerals peaks in
the XRD plot was found to decrease when the soil was treated with LISS at the
double chemical ratio. The FESEM and XRD results suggest the formation of
products formed by the reactions of clay particles with the LISS additive. Moreover,
the moisture content of soil gradually decreased by around 3%, and the grain size
of the treated soils varied with an increase in curing time period, indicating the
progressive utilization of water to form reaction products that can bind the clay
particles and result in improvement in engineering properties of problematic soils.
The pH of LISS increased from 3 to 7.8 in 20 days, which exhibited a progressive
chemical reaction in this period of time. However, the consistency limits of LISS
treated soils before and after treatments were nearly the same and no major
enhancements were noted in the consistency limit values.
In order to evaluate the feasibility of using LISS as an alternative soil
stabilizer, two case study examples involved with pavement design and slope
viii
stability were analyzed. From the results and analysis of the modeling, the
pavement design life of treated expansive soil was higher than that of untreated
expansive soils. Also, the global factor of safety (FOS) of treated Dallas soil was
slightly increased by 13% as compared to the section without any soil treatment.
More studies and field treatment sections will provide more insights into the
effectiveness of LISS treatments to enhance soil properties that can provide better
support of civil infrastructure.
ix
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ................................................................................... iii
ABSTRACT .............................................................................................................v
LIST OF ILLUSTRATIONS ............................................................................... xvi
LIST OF TABLES ............................................................................................... xxi
Chapter 1 INTRODUCTION ...................................................................................1
1.1 General ...............................................................................................1
1.2 Research Objectives ...........................................................................6
1.3 Organization of the Dissertation ........................................................7
Chapter 2 LITERATURE REVIEW ......................................................................10
2.1 Clay Mineralogy ..............................................................................11
2.1.1 General ..................................................................................... 11
2.1.2 Kaolinite ................................................................................... 14
2.1.3 Illite .......................................................................................... 16
2.1.4 Montmorillonite ....................................................................... 18
2.2 The Mechanisms of Clay-Water Interaction ....................................21
x
2.3 Expansive Soils ................................................................................24
2.4 Problems Caused by Expansive Soils ..............................................25
2.4.1 Pavement Failures .................................................................... 27
2.4.2 Foundation Failures ................................................................. 30
2.4.3 Slope Failures........................................................................... 32
2.5 Brief Introduction of Soil Stabilizer And Its Stabilization Mechanism
............................................................................................................................34
2.5.1 General ..................................................................................... 34
2.5.2 Traditional Stabilizers .............................................................. 35
2.5.2.1 Lime Stabilizers ................................................................ 35
2.5.2.2 Cement Stabilizers ............................................................ 37
2.5.2.3 Fly Ash Stabilizers ............................................................ 39
2.5.3 By-product Stabilizers ............................................................. 41
2.5.3.1 Enzyme Stabilizers............................................................ 42
2.5.3.2 Geopolymer Stabilizers ..................................................... 44
2.5.3.3 Ionic Stabilizers ................................................................ 44
2.5.4 Comparison of Traditional Stabilizers and Non-traditional
Stabilizers .......................................................................................... 47
xi
2.6 Effect of LISS on the Soil per Previous Studies ..............................48
2.7 Summary ..........................................................................................49
Chapter 3 ................................................................................................................51
Experiment proGram .............................................................................................51
3.1 Introduction ......................................................................................51
3.2 Physical, Chemical and Microstructural Studies of Test Soils ........55
3.2.1 Physical Tests........................................................................... 55
3.2.1.1 Specific Gravity and Grain Size Distribution Tests .......... 55
3.2.1.2 Consistency Limits Tests .................................................. 56
3.2.1.3 Standard Proctor Compaction Tests.................................. 57
3.2.2 Chemical Tests ......................................................................... 58
3.2.2.1 Clay Mineralogy Measurement of Soil ............................. 58
3.2.2.2 pH Test .............................................................................. 62
3.2.3 Microstructural Tests ............................................................... 62
3.2.3.1 Field Emission Scanning Electron Microscope (FESEM)
Test ............................................................................................................ 63
3.2.3.2 Energy Dispersive X-ray Spectroscopy (EDS) ................. 65
3.2.3.3 Powder X-ray Diffraction (XRD) Analysis ...................... 65
xii
3.3 Engineering Tests.............................................................................67
3.3.1 Unconfined Compressive Strength (UCS) Tests ..................... 68
3.3.2 Resilient Modulus (MR) Tests .................................................. 69
3.3.3 1-D Swell Test ......................................................................... 71
3.3.4 Fatigue of Swelling Test .......................................................... 72
3.3.5 Linear Shrinkage Strain Test ................................................... 72
3.3.6 Direct Shear Test...................................................................... 73
3.4 Assessment of Stabilization Mechanism .........................................74
3.4.1 Variations in pH ....................................................................... 74
3.4.2 Variations in Moisture Content ................................................ 75
3.4.3 Variations in Consistency Limits for Treated Soils ................. 76
3.5 Numerical Modeling ........................................................................76
3.6 Summary ..........................................................................................77
Chapter 4 The EFFECT OF LISS ON EXPANSIVE SOILS IN PHYSICAL and
ENGINEERING TESTS ........................................................................................79
4.1 Introduction ......................................................................................79
4.2 Physical Tests...................................................................................79
4.2.1 Standard Compaction Test ....................................................... 79
xiii
4.2.2 Consistency Limits Tests ......................................................... 81
4.3 Engineering Tests.............................................................................82
4.3.1 Unconfined Compressive Strength (UCS) Test ....................... 82
4.3.1.1 Dallas Soil ......................................................................... 82
4.3.1.2 Carrollton Soil ................................................................... 85
4.3.1.3 Summary ........................................................................... 88
4.3.2 Repeated Load Triaxial Test (RLT) to Determine Resilient
Modulus (MR) .................................................................................... 88
4.3.3 Universal Model for Predicting Mr Value ............................... 92
4.3.3.1 Dallas Soil ......................................................................... 92
4.3.3.2 Carrollton Soil ................................................................... 94
4.3.4 Linear Shrinkage Test .............................................................. 97
4.3.5 One-Dimensional Swell Test ................................................... 98
4.3.6 Fatigue of Swelling Test ........................................................ 102
4.4 Summary ........................................................................................104
Chapter 5 STABILIZATION MECHANSIMS OF LISS TREATMENT ON
EXPANSIVE SOIL .............................................................................................105
5.1 General ...........................................................................................105
xiv
5.2 Microstructural Tests .....................................................................105
5.2.1 Field Emission Scanning Electron Microscope (FESEM) Test
......................................................................................................... 106
5.2.2 Energy Dispersive X-Ray Spectroscopy (EDS) Tests ........... 109
5.2.3 Powder X-Ray Diffraction (XRD) Test ................................. 112
5.3 Additional Tests .............................................................................115
5.3.1 Changes in Water Content ..................................................... 115
5.3.2 Variation of pH ...................................................................... 117
5.3.3 Variation in Consistency Limits ............................................ 120
5.4 Probable Stabilization Mechanisms ...............................................121
Chapter 6 CASE STUDIES AND MODELING .................................................124
6.1 Pavement Design Case Study .....................................................124
6.2 Slope Stability Case Study .........................................................129
Chapter 7 SUMMARY OF FINDINGS AND FUTURE RECOMMENDATIONS
..............................................................................................................................134
7.1 Introduction ....................................................................................134
7.2 Summary of Findings .....................................................................135
7.2.1 Findings from Physical, Chemical and Engineering Tests .... 135
xv
7.2.2 Findings in Microstructural, Additional Tests and Numerical
Modeling results .............................................................................. 138
7.3 Future Recommendations ..............................................................141
REFERENCES ....................................................................................................142
xvi
LIST OF ILLUSTRATIONS
Figure 1.1 Expansive soil distribution throughout the United States (Source:
http://www.tellafirma.com/find-texas-expansive-soils) ......................................... 5
Figure 2.1 Silicon tetrahedral and octahedral units (Genedy et al. 2014)............. 13
Figure 2.2 Synthesis pattern for three common clay minerals (Chittoori 2008) .. 14
Figure 2.3 Schematic diagrams of the structure of kaolinite (Aboudi Mana et al.
2017) ..................................................................................................................... 15
Figure 2.4 SEM image of kaolinite (Source: http:// webmineral.com/ specimen
s/picshow.php?id=1283#.XHNZZuhKg2w) ......................................................... 16
Figure 2.5 Schematic diagrams of the structure of Illite (muscovite)................... 17
Figure 2.6 SEM imagine of Illite (Source: http:// webmineral.com/ specimens/
picshow.php?id=1284#.XHNZEOhKg2w) .......................................................... 18
Figure 2.7 Schematic diagrams of the structure of Montmorillonite (Zhu et al. 2016)
............................................................................................................................... 19
Figure 2.8 Atomic structure of Montmorillonite (Grim 1953) ............................. 20
Figure 2.9 SEM imagine of Montmorillonite (Source: http:// webmineral.com/
specimens/picshow.php?id=1285&target=Montmorillonite#.XHL9VOhKg2w) 20
Figure 2.10 Clay particle and surface charge display (Source: http:// ees2.geo.rpi.e
du/geo1/lectures/lecture6/Weathering_07.html) ................................................... 22
xvii
Figure 2.11 The comparison between adsorbed water layers on Montmorillonite
and kaolinite (Lambe 1958) .................................................................................. 23
Figure 2.12 Distributions of ions adjacent to a clay surface in a diffuse double layer
(Mitchell and Soga 2005)...................................................................................... 23
Figure 2.13 Expansive soil distribution throughout the United States (Witczak
1972) ..................................................................................................................... 25
Figure 2.14 The annual cost of damage to structures built on expansive soils in the
United States since 1973(Adem and Vanapalli 2016) .......................................... 27
Figure 2.15 Crack types on pavements built on expansive soils (Dafalla and
Shamrani 2011) ..................................................................................................... 29
Figure 2.16 Longitudinal cracks in a road pavement in Texas (Zornberg and Gupta
2009) ..................................................................................................................... 30
Figure 2.17 Building foundation failure (Al-Rawas and Goosen 2006) ............... 31
Figure 2.18 Damage to home supported on shallow piles (Rogers et al. 1993) ... 32
Figure 2.19 (a) Grapevine dam surficial slope failure, (b) Randell lake slope failure
in North Texas....................................................................................................... 34
Figure 2.20 Flocculation and agglomeration (Prusinski and Bhattacharja 1999) . 37
Figure 2.21 Comparison of resilient modulus for untreated, lime-treated and
cement-lime- treated soils at the deviator stress= 68.9 kPa (Puppala 2008) ........ 39
Figure 2.22 Proposed enzyme stabilization mechanism (Tingle et al. 2007) ....... 43
xviii
Figure 2.23 Proposed stabilization mechanisms of ionic soil stabilizer (Tingle et
al. 2007) ................................................................................................................ 46
Figure 2.24 Model of ionic soils stabilizer reducing water film (Xiang et al. 2010)
............................................................................................................................... 47
Figure 3.1 LISS: Concentration liquid chemical and surfactant ........................... 53
Figure 3.2 Deep injection rake for pressurized injection of LISS (Source:
http://www.prochemtex.com/Services.html) ........................................................ 53
Figure 3.3 Flowchart for the research tasks .......................................................... 54
Figure 3.4 The E-180 plastic limit rolling device (He et al. 2018a) ..................... 56
Figure 3.5 Flowchart of detailed procedures for CEC (Gautam 2018)................ 59
Figure 3.6 Flow chart of determining TP in the soil (Chittoori 2008) .................. 60
Figure 3.7 Flow chart for the SSA test (Chittoori 2008) ...................................... 61
Figure 3.8 pH test device ...................................................................................... 62
Figure 3.9 CRC-100 sputtering machine .............................................................. 64
Figure 3.10 Hitachi S-4800N variable pressure FESEM ...................................... 64
Figure 3.11 Hitachi S-3000N SEM-EDS .............................................................. 65
Figure 3.12 Bruker D8 x-ray diffractometer machine .......................................... 67
Figure 3.13 Geocomp triaxial machine ................................................................. 69
Figure 3.14 Resilient modulus test setup .............................................................. 70
Figure 3.15 1-D Swell test setup ........................................................................... 71
Figure 3.16 Linear shrinkage bar test setup .......................................................... 73
xix
Figure 4.1 Standard Compaction Curve for Expansive Soils Before and after
Treatment. (a) Dallas Soil. (b) Carrollton Soil ..................................................... 80
Figure 4.2 UCS Test Results of Dallas Soil. (a) Dallas Soil-First Ratio Treatment.
(b) Dallas Soil-Second Ratio Treatment. (c) Dallas Soil-Third Ratio Treatment. (d)
Effect of LISS Dosages and Curing Time on UCS ............................................... 84
Figure 4.3 UCS test results of Carrollton soil. (a) Carrollton Soil-First Ratio
Treatment. (b) Carrollton Soil-Second Ratio Treatment. (c) Carrollton Soil-Third
Ratio Treatment. (d) Effect of LISS dosages and curing time on UCS ................ 87
Figure 4.4 Resilient Modulus of Dallas soil before and after treatment ............... 94
Figure 4.5 Resilient Modulus of Carrollton soil before and after treatment ......... 96
Figure 4.6 Swell potential of Dallas soil. (a) Dallas Soil-First Ratio Treatment. (b)
Dallas Soil-Second Ratio Treatment. (c) Dallas Soil-Third Ratio Treatment .... 100
Figure 4.7 Swell potential of Carrollton soil. (a) Carrollton Soil-First Ratio
Treatment. (b) Carrollton Soil-Second Ratio Treatment. (c) Carrollton Soil-Third
Ratio Treatment .................................................................................................. 101
Figure 4.8 Fatigue of swelling. (a) Dallas Soil. (b) Carrollton Soil.................... 103
Figure 5.1 FESEM images of Dallas soil. (a) control sample. (b) treated sample
after 28 days ........................................................................................................ 107
Figure 5.2 FESEM of Carrollton soil. (a) control sample. (b) treated sample after
28 days ................................................................................................................ 108
Figure 5.3 The FESEM sideview image of expansive soil after treatment ....... 109
xx
Figure 5.4 The effect of a high pH system is to release silica and aluminum from
the clay surface (Little 1995) .............................................................................. 110
Figure 5.5 XRD analysis of expansive soils. (a) Dallas soil. (b) Carrollton soil 114
Figure 5.6 Variation of moisture content after third ratio treatment. (a) Dallas soil.
(b) Carrollton soil ................................................................................................ 116
Figure 5.7 Variation of pH after the third ratio treatment. (a) Dallas soil (48 hours).
(b) Dallas soil (20 days) ...................................................................................... 118
Figure 5.8 Variation of pH after the third ratio treatment. (a) Carrollton soil (48
hours). (b) Carrollton soil (20 days) ................................................................... 119
Figure 5.9 The texture change of expansive soil before and after treatment ...... 121
Figure 6.1 Pavement location (1311 FM 1807, Venus, Texas) .......................... 125
Figure 6.2 Bar chart of pavement life of flexible base located on expansive subgrade
soils before and after treatment ........................................................................... 128
Figure 6.3 The desiccation cracks in the upper side of the slope ....................... 129
Figure 6.4 The geometric configuration of the slope .......................................... 130
Figure 6.5 The geometry of slope in the software .............................................. 132
Figure 6.6 FOS of slope with untreated and treated Dallas soil ......................... 133
xxi
LIST OF TABLES
Table 2.1 Comparison of Lime, Cement, and Fly Ash (Chittoori 2008) .............. 41
Table 3.1 Three LISS Ratios Considered for Soil Treatment Studies .................. 54
Table 3.2 Physical Test for Control Soils ............................................................. 57
Table 3.3 Mineralogical Tests Performed on Two Soils ...................................... 58
Table 3.4 Clay Mineralogy Contents of Two Soils .............................................. 59
Table 4. 1 Three LISS ratios for Consistency Limits on two expansive soils ...... 81
Table 4.2 Resilient Modulus of soils before and after treatment. (a) Dallas soil (b)
Carrollton Soil ....................................................................................................... 90
Table 4.3 Dallas Soil-Regression coefficients of resilient modulus and coefficient
determination before and after treatment .............................................................. 94
Table 4.4 Carrollton Soil-Regression coefficients of resilient modulus and
coefficient determination before and after treatment ............................................ 97
Table 4.5 Three LISS Ratios for Consistency Limits of Two Expansive Soils .... 98
Table 5.1 Al/Si ratio change for Dallas and Carrollton soil before and after
treatment ............................................................................................................. 111
Table 5.2 Al/Si ratio change for Dallas and Carrollton surface reaction products
after treatment ..................................................................................................... 111
Table 5.3 Variation in Consistency Limits with curing time .............................. 121
Table 6.1 The properties of subgrade Dallas soil before and after treatment ..... 127
Table 6.2 The properties of subgrade Carrollton soil before and after treatment 127
xxii
Table 6.3 The pavement design life of flexible base on untreated and treated
Expansive soil ..................................................................................................... 128
Table 6.4 Basic properties of Dallas soil before and after treatment .................. 132
1
Chapter 1
INTRODUCTION
1.1 General
Expansive soils are widely distributed in the arid and semi-arid regions
around the world (Al-Rawas and Goosen 2006), and tend to experience excessive
changes in volume during the ingress and egress of water due to changes and
fluctuations in the moisture content in soils (Punthutaecha et al. 2006, Jones and
Jefferson 2012, Pranav et al. 2012). Expansive soils can absorb a significant amount
of water after rainfall and swell substantially, but during the drought seasons, they
lose moisture and shrink, often resulting in desiccation cracks. The swell-shrink
behavior of expansive soil is not completely reversible. The recurring cracks on the
ground surface that do not seal perfectly after re-wetting become a source of
potential problems (Jones and Jones 1987, Jones and Jefferson 2012). Every year,
the State of Texas spends at least $1 billion to repair damaged houses, pavements,
buried utilities, and embankments established on expansive soils; the estimated
annual damage of facilities built on expansive soils in the United States is over $9
billion (Punthutaecha et al. 2006, Zhao et al. 2014, He et al. 2018a).
Various treatment methods have been developed and used over the past
decades to prevent or mitigate the losses incurred due to the swell-shrink behavior
of expansive soils. Most often, conventional soil stabilizers, including lime,
Portland cement, fly ash, or a combination of them are utilized to improve the
2
workability of the soil, reduce swell and shrinkage behavior, and enhance the
strength and stiffness properties of the foundation soil of residential homes and
subgrades of pavements (Katz et al. 2001, Rauch et al. 2002, Zhang et al. 2013,
Puppala et al. 2014b). However, calcium-based stabilizers have a negative impact
on sulfate-rich expansive soils that leads to excessive volume changes and heaving
(Katz et al. 2001, Rauch et al. 2002). Such phenomenon occurs when the calcium
in the stabilizer reacts with sulfate and alumina in the soil to form ettringite (Rauch
et al. 1993, 2002, Puppala et al. 2014b). Because of crystal growth due to hydration
reactions, ettringite tends to swell up to 250% when it comes in contact with water
(Adams et al. 2008, Zhang et al. 2015). Furthermore, conventional soil stabilizers
are harmful to the environment. For instance, lime treatment dramatically raises the
pH of the soil, and its production emits a large amount of carbon dioxide, which
exacerbates the global greenhouse effect (Zhang et al. 2013).
Due to the reasons mentioned above, non-traditional stabilizers that do not
have calcium as one of the main constituents are emerging in the market for the
treatment of sulfate-rich soils. Most non-traditional stabilizers are classified into
three categories: ionic, polymer, or enzyme (Rauch et al. 1993, 2002). Some of the
products also contain secondary additives, including surfactants, catalysts, and
ultraviolet inhibitors (Tingle et al. 2007). In the field, several trucks are required to
freight tons of traditional stabilizers for treating expansive soil, whereas non-
traditional chemical stabilizers are available as concentrated liquids. They are
3
diluted with water at the site, and then pressure-injected into the deep layers of soils
or spread on the surface of the problematic soil. Furthermore, according to the
description from the manufacturer, LISS is able to treat up to 30000 sq. ft. in one
day (Scott 2019). This leads to a reduction in the transportation cost and time of
non-traditional stabilizers such as LISS, as compared to the traditional soil
stabilizers (Katz et al. 2001).
Despite being environmentally friendly and having several benefits as
mentioned above, many engineers and manufacturers are reluctant to accept LISS
as a viable stabilization alternative to treat problematic expansive soils. The lack of
acceptance can be attributed to a number of issues that are listed below:
1. Published and independent studies of non-traditional stabilizers are insufficient,
and the test results provided by the suppliers are not convincing.
2. Knowledge of the stabilization mechanisms of non-traditional stabilizers is
limited.
3. There is a lack of laboratory test methods that can be utilized to effectively
predict the in-situ performance of LISS-treated soils. Well-established methods
are thus required to select the optimum dilution ratio of certain ionic products
to improve the properties of a specific soil.
4. The information provided by the suppliers about the ionic stabilizers is not
adequate. Many companies regard LISS as the proprietary, which makes it even
4
more difficult for researchers to evaluate the stabilization mechanism and
efficiency of treatment (Rauch et al. 1993).
Several research studies highlighted significant improvements in
engineering properties of expansive soils upon treatment with LISS additives
(Dong et al. 2004, Xiang et al. 2010, Wang and Liu 2011, Alhassan and Olaniyi
2013, Latifi et al. 2015, Zhang et al. 2018, Gautam 2018, Hariharan et al. 2018, He
et al. 2018c, 2018b, 2018a). Contrarily, some research studies reported no
appreciable improvement in engineering properties when some fat clay, lean clay,
and elastic silts were treated with LISS (Rauch et al. 1993, 2002, Katz et al. 2001).
The majority of literature that reported successful treatment of problematic soils
summarized the improvements based on engineering properties, such as soil
strength and volumetric changes (Zhao et al. 2014, He et al. 2018c, 2018b, 2018a).
Unfortunately, these studies did not highlight the fundamental mechanisms
responsible for the time-dependent improvement in engineering properties of
treated expansive soils; therefore, further studies involving extensive laboratory
experiments are necessary for evaluating the effects of different dosages of LISS
on problematic soils and understanding the stabilization mechanisms from
microanalysis studies.
In this study, LISS was used to treat expansive soils collected from Dallas
and Carrollton, Texas, both of which have a high frequency of expansive soil
(Figure 1.1). LISS is composed of sulfuric acid, phosphoric acid, citric acid, water,
5
and a surfactant. The performance of the treated soils was analyzed based on the
results of a series of tests, including physical, chemical, engineering, and
microstructural tests. The efficacy of LISS was evaluated by studying the
improvements in the engineering properties of the problematic soils and comparing
them to the untreated control specimens. Microstructural analysis tests were
performed to comprehend the probable stabilization mechanisms and gain some
fundamental understanding of the reasons behind the improvement in engineering
properties of LISS-treated soils with different curing times. Two hypothetical case
studies, including remedying a slope which incurred a surficial failure and treating
a problematic subgrade soil using LISS, were analyzed to assess the applicability
of using the ionic stabilizer to improve the performance of geotechnical
infrastructures. These analyses were performed using soil properties obtained from
laboratory testing before and after treatment.
Figure 1.1 Expansive soil distribution throughout the United States (Source:
http://www.tellafirma.com/find-texas-expansive-soils)
6
1.2 Research Objectives
The primary objective of this research was to determine the probable
stabilization mechanisms by which a liquid ionic stabilizer improves the
engineering properties of problematic expansive soils. To address this objective, a
locally available stabilizer that has been extensively used in Texas for a couple of
decades to treat subgrades efficiently and effectively was considered as the main
ionic stabilizer. Several specific objectives were formulated, which are listed in the
following:
1. Study and evaluate the effectiveness of treatment on selected soils at different
application dilution ratios.
2. Investigate and identify the mechanisms by which clayey soils are modified or
stabilized by LISS (Comprehensive mineralogical studies were designed to
address this objective).
3. Study and investigate soil strength and volume change properties of expansive
soils modified at different dilution ratios.
4. Study the improvement in performance of geotechnical infrastructures by
considering hypothetical case scenarios in which LISS is used to stabilize the
surficial slope of a failed embankment and to enhance the performance of a
pavement section by stabilizing the subgrade soil.
7
1.3 Organization of the Dissertation
This dissertation consists of seven chapters. Chapter 1 introduces the topic
and provides some background information about the chemical stabilization of
problematic soils. The purpose and specific objectives of this research study are
highlighted to emphasize the necessity and importance of this study.
Chapter 2 presents the salient findings of a thorough review of existing
literature on properties of expansive soils and its behavior when exposed to
moisture and highlights the detrimental impacts the swell-shrink behavior of
expansive soils has on the overlying civil infrastructures. Various stabilizers used
to mitigate the damage caused by expansive soils, including traditional stabilizers
and non-traditional stabilizers, with emphasis on the liquid ionic soil stabilizer
(LISS), are introduced in detail. Previous studies related to the effects of LISS on
the engineering properties of expansive soil are also summarized in this chapter.
Chapter 3 includes the framework of the current research. The basic soil
properties and the selection of soils are covered in this chapter. The details of the
experimental programs, including engineering, physical, chemical and
microstructural tests are elucidated. The procedure adopted to select the optimum
LISS dosage, based on the engineering test results, is presented in this chapter,
along with the method followed to comprehend the probable stabilization
mechanisms. Two case studies, including slope and pavement design, are
introduced that were used to evaluate the effectiveness of LISS treatment of
8
expansive soils. The laboratory test procedures, devices, and methods of the
different tests are explained in this chapter.
Chapter 4 summarizes the laboratory test results of both untreated and
treated soils, including Consistency Limits, standard Proctor compaction,
unconfined compressive strength (UCS), resilient modulus, 1-D swell, fatigue
swelling, and linear shrinkage bar test results. The test results are analyzed in this
chapter to determine the optimum LISS dosage. In addition, the applicability of
LISS treatment to enhance the performance of geotechnical infrastructures is
assessed.
Chapter 5 focuses on the probable mechanism responsible for the
improvement of engineering properties of LISS-treated soils. The probable
mechanism is postulated based on the analyses of Field Emission Scanning
Electron Microscope (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), and
X-ray Powder Diffraction (XRD) results before and after treatment. The variations
in moisture content, pH, Consistency limits, and grain size distribution of treated
soils, with curing period, are used as supplementary evidence that support the
hypothesized stabilization mechanism.
Chapter 6 includes descriptions of two case studies related to slope failure
and pavement design that are used to assess the suitability of implementing LISS
treatment as a viable option for treating expansive soils.
9
Chapter 7 summarizes the findings of the research study, expounds on
conclusions drawn from the analysis of test results, and makes recommendations
for the scope of future research.
10
Chapter 2
LITERATURE REVIEW
Expansive soils have a detrimental effect of the performance of overlying
infrastructures and require recurring repair works that cost billions of dollars (Jones
and Holtz 1973, Puppala and Cerato 2009, Puppala et al. 2016, Atahu et al. 2019).
These problematic soils exhibit significant swelling and shrinkage when exposed
to variations in moisture content (Adem and Vanapalli 2015, Yixian et al. 2016,
Belchior et al. 2017, Gupta et al. 2017, Soltani et al. 2017, Atahu et al. 2019, Julina
and Thyagaraj 2019). The prominent swell-shrink behavior of expansive clay, when
exposed to moisture, primarily depends on the mineralogy of the predominant clay
minerals such as Montmorillonite (Liu et al. 2015, Shahbazi et al. 2017, Ural 2018,
Lu et al. 2019). Expansive soils inevitably swell when they absorb the water after
rainfall events and shrink due to loss of water during prolonged dry phases.
The characteristics of different clay minerals were thoroughly reviewed and
are summarized in Section 2.1. The interaction between clay and water is briefly
introduced in Section 2.2. Due to the swell-shrinkage behavior of expansive clays
when exposed to water, the problems caused by them are elaborated on in Sections
2.3 and 2.4. In order to mitigate the losses caused by expansive soils, different
chemical stabilization methods, including traditional, nontraditional, and by-
product stabilizers, are often used to stabilize the soils. These methods are discussed
in detail in Section 2.5, where the benefits and shortcomings of the chemical
11
stabilizers are scrutinized. The salient findings of the limited research work on the
use of LISS treatment of expansive soils around the world were also reviewed, and
the lacunae in the available information that led to this research study are identified
in Section 2.6. All detailed information about the above testing is described below.
2.1 Clay Mineralogy
2.1.1 General
The soil classification system defines clay particles according to an
effective diameter of two microns or less (Sedmale et al. 2017, Liu et al. 2018).
However, soils cannot be merely classified based on particle size, as the behavior
of different clay types primarily depends on the mineralogical composition (Chen
2012). Clay minerals are crystalline materials formed by chemical weathering of
different rock-forming minerals (Holtz and Kovacs 1981, Pedarla 2013). In fact,
clay minerals belong to the mineral family called phyllosilicates, in which the
structures of common layer silicate are composed of tetrahedral and octahedral
units (Mitchell and Soga 2005). Schematic representation of these tetrahedral and
octahedral sheets (Figure 2.1). The tetrahedral sheet is composed of silica
tetrahedral units, in which the Si4+ cation is surrounded by four oxygen atoms on
all four sides. The octahedral sheet consists of octahedral units, in which six
oxygens or hydroxyls groups surround the central magnesium or aluminum atoms
(Holtz and Kovacs 1981, Mitchell and Soga 2005, Karpiński and Szkodo 2015,
12
Zhang et al. 2016, Liu et al. 2018, Ural 2018). Although different clay minerals are
characterized by the stacking arrangements of these two sheets, the three most
common groups of clay minerals are kaolinite, Illite, and Montmorillonite (Figure
2.2) (Bell 1996).
Kaolinite, the principal component of china clay, is a phyllosilicate mineral
that is widely found in warm and moist regions. Illite is a group of non-expansive
clay minerals that is found predominately in marine clays and shales.
Montmorillonite is a member of smectite that results from the weathering of rock
rich in Calcium (Ca) and Magnesium (Mg), and has a high swell-shrinkage
potential (Grim 1953, Chittoori 2008). These minerals are relatively small, and are
present in varying proportions in different types of soil. The type and quantity of
the constituent clay minerals indictate the behavior of different soils (Pedarla 2013).
The composition of soil can be determined via cation exchange capacity
(CEC), total potassium (TP), and specific surface area (SSA), based on the methods
described by Chittoori (2008) and Chittoori and Puppala (2011). CEC is defined as
the sum of exchangeable cations balancing the negative charge in clay particles,
and is expressed in milliequivalent per 100 grams of soil (Chapman 1965, Grim
1968, Nelson and Miller 1997, Mitchell and Soga 2005, Chittoori and Puppala 2011,
Chen 2012). In general, a high swelling potential of a soil indicates a high CEC
value due to a high surface activity (Nelson and Miller 1997). Specific surface area
or SSA is the total surface area of a material per unit of mass or bulk volume(Holtz
13
and Kovacs 1981). Generally, soils with smaller particles have a larger specific
surface area. A typical example of a soil with high SSA is bentonite
(Montmorillonite), which has a high SSA of 600-800 m2/g (Mitchell and Soga
2005). The high surface area of clayey soils is also associated with a high negative
surface charge that attracts water and leads to substantial swelling when exposed to
water. Owing to the high SSA, clayey soils with high ontmorillonite content are
prone to have a higher swell potential. TP is used to test potassium content in the
clay, which reflects the content of Illite. Marine clay, with high Illite content, is
regarded as non-expandable clay. The test process and detailed information of CEC,
TP, and SSA are explained in the next chapter.
Figure 2.1 Silicon tetrahedral and octahedral units (Genedy et al. 2014)
14
Figure 2.2 Synthesis pattern for three common clay minerals (Chittoori 2008)
2.1.2 Kaolinite
Kaolinite (Al2Si2O5(OH)4), is a dioctahedral 1:1 mineral, with the basic unit
consisting of one sheet of silica tetrahedral and one sheet of aluminum octahedral.
It is formed by the weathering of feldspar and mica, and is a major component of
china clay (Holtz and Kovacs 1981) (Pedarla 2013, Sun et al. 2016, Deng et al.
2017, Su et al. 2017) (Figure 2.3). The strong hydrogen bonds and Van der Waals
force between the two basic units of kaolinite prevent the intrusion of water and
subsequent swelling (Deng et al. 2017, Su et al. 2017). Therefore, kaolinite does
not have a high propensity for swelling, and hence has a very low value of CEC (3
to 15 meq/100g) (Holtz and Kovacs 1981, Nelson and Miller 1997, Mitchell and
15
Soga 2005). Figure 2.4 presents the SEM image of kaolinite, which shows the plate-
like structure of the individual crystals. These kaolinite platelets gradually
accumulate to form large aggregates with a ‘booklet’ structure (Christidis 2013,
Wilson et al. 2014, Dedzo and Detellier 2016, Mansa et al. 2017). The specific
surface of the kaolinite ‘booklets’ is very small (10-20 m2/g), which reduces the
plasticity and water-holding capacity (Holtz and Kovacs 1981, Chittoori 2008,
Dedzo and Detellier 2016).
Figure 2.3 Schematic diagrams of the structure of kaolinite (Aboudi Mana et al.
2017)
16
Figure 2.4 SEM image of kaolinite (Source:
http://webmineral.com/specimens/picshow.php?id=1283#.XHNZZuhKg2w)
2.1.3 Illite
Illite, one of the fundamental clay minerals in the soil, was first discovered
and named by Professor R.E. Grim at the University of Illinois (Holtz and Kovacs
1981, Wang et al. 2017a). Illite is one of the primary clay minerals in argillaceous
rocks, and is formed by the weathering of feldspar and degradation of muscovite
(Chittoori 2008, Pedarla 2013).
The basic structural unit is composed of one central octahedral sheet
sandwiched between two silica tetrahedral sheets (Figure 2.5). As one-fourth of the
silicon is replaced by aluminum, and the charge deficiency is balanced by
potassium present between the two layers, the cation exchange capacity of Illite is
17
higher than kaolinite (10-40 meq/100g) (Grim 1968, Nelson and Miller 1997,
Mitchell and Soga 2005, Zhang et al. 2016). Figure 2.6 shows the SEM image of
small and flaky particles of Illite, along with other clay minerals. The specific
surface area of Illite ranges from 65 to 100m2/g, which suggests that the swell
potential of Illite is slightly higher than that of kaolinite (Mitchell and Soga 2005).
Figure 2.5 Schematic diagrams of the structure of Illite (muscovite)
18
Figure 2.6 SEM imagine of Illite (Source:
http://webmineral.com/specimens/picshow.php?id=1284#.XHNZEOhKg2w)
2.1.4 Montmorillonite
Montmorillonite is the most important member of the smectite family and
is classified as a 2:1 mineral group. Similar to Illite, it consists of two silicon
tetrahedral sheets and one aluminum octahedral sheet (Figure 2.7) (Holtz and
Kovacs 1981, Avisar et al. 2010, Segad et al. 2010). In the basic unit of
Montmorillonite, the octahedral sheet contains aluminum, magnesium, or iron, and
is sandwiched between two silica sheets coordinated with oxygen and hydroxyls
(Figure 2.8) (Holtz and Kovacs 1981, Chittoori 2008, Segad et al. 2010, Pedarla
2013). The bonding between the two silica sheets in Montmorillonite is very weak
compared to the potassium bonds in Illite or the hydrogen bonds in kaolinite.
19
Consequently, water and other exchangeable ions can easily separate the basic
layers that swell significantly in the presence of moisture (Grim 1953, 1968).
Montmorillonite is composed of extremely small units of 1 nm thickness
that are flaky shape (Figure 2.9). Due to the small particle size and weak interlayer
bonding, Montmorillonite has a high specific surface area (600-800 m2/g) and CEC
value (80-150 meq/100g) (Holtz and Kovacs 1981, Nelson and Miller 1997,
Mitchell and Soga 2005, Chittoori 2008). The volume of clay with significant
Montmorillonite content may increase more than fifteen times after absorbing the
water; thereby causing significant damage to overlying infrastructures built on
these expansive soils (Kaur and Kishore 2012, Katti et al. 2015).
Figure 2.7 Schematic diagrams of the structure of Montmorillonite (Zhu et al.
2016)
20
Figure 2.8 Atomic structure of Montmorillonite (Grim 1953)
Figure 2.9 SEM imagine of Montmorillonite (Source:
http://webmineral.com/specimens/picshow.php?id=1285&target=Montmorillonite
#.XHL9VOhKg2w)
21
2.2 The Mechanisms of Clay-Water Interaction
Clayey soils have a high affinity for water because of their small particle
size and high surface activity. This affinity for water can be attributed to hydrogen
bonding (oxygen or hydroxyl molecules attract the hydrogen of water), van der
Waals attractions, and charged surface-dipole attractions (Figure 2.10) (Murray and
Quirk 1980, Ural 2018). Among these different types of bonding, the hydrogen
bonding is the strongest and is considered to be the primary reason behind the
swelling of expansive soils due to water absorption (Holtz and Kovacs 1981). In
the clay-water system, some molecular layers of water, designated as adsorbed
water, surround the clay particles and are tightly held by the clay surface (Chen
2012). Figure 2.11 presents a schematic representation of the comparison between
adsorbed water layers of Montmorillonite and kaolinite. Although the thickness of
absorbed water is almost the same in both cases, the size of the kaolinite particle
far outweighs that of the Montmorillonite. This indicates that Montmorillonite has
a higher propensity towards moisture than kaolinite to a undergo larger volume
changes when exposed to water (Holtz and Kovacs 1981).
The clay particles hold a high concentration of cations to balance the
negative surface charge attributed to the presence of broken bonds and isomorphous
substitution. These cations are termed as ‘adsorbed cations’ and are strongly held
by the negatively charged clay particles. The cations tend to diffuse away from the
clay surface in order to balance the low cation concentration within the absorbed
22
water. However, this kind of diffusion is offset by the electrostatic attraction
between the positively charged cations to the negatively charged clay surface,
which is more dominant close to the clay particles. The negatively-charged clay
surface, along with the strongly held cations (close to the clay particle) and the
relatively loosely held diffused cations (further away from the clay particle), form
the diffuse double layer (Holtz and Kovacs 1981, Mitchell and Soga 2005). Figure
2.12 shows the distribution of ions adjacent to a clay surface in a diffuse double
layer (Holtz and Kovacs 1981, Mitchell and Soga 2005). The diffuse double layer
governs the clay-water interaction and affects the engineering properties of clay,
including swelling and plasticity (Mitchell and Soga 2005).
Figure 2.10 Clay particle and surface charge display (Source:
http://ees2.geo.rpi.edu/geo1/lectures/lecture6/Weathering_07.html)
23
Figure 2.11 The comparison between adsorbed water layers on Montmorillonite
and kaolinite (Lambe 1958)
Figure 2.12 Distributions of ions adjacent to a clay surface in a diffuse double
layer (Mitchell and Soga 2005)
24
2.3 Expansive Soils
In general, expansive soils are clayey soils with a high specific surface area
and cation exchange capacity that usually have a Montmorillonite content
(Madhyannapu et al. 2009, Wanyan et al. 2010, Pedarla et al. 2011, Puppala et al.
2014a, Liu et al. 2015, Sharma and Sivapullaiah 2016, Yixian et al. 2016, Shahbazi
et al. 2017). They tend to undergo large volume changes when exposed to variations
in moisture content, and have a detrimental impact on the service life and
performance of overlying structures (Puppala et al. 2014a, Liu et al. 2015, Adem
and Vanapalli 2016, Sharma and Sivapullaiah 2016, Yixian et al. 2016, James and
Pandian 2016, Belchior et al. 2017, Alazigha et al. 2018b, Banerjee et al. 2018c,
Biswas and Ghosh 2018, He et al. 2018a, George et al. 2019b, Huang et al. 2019).
Expansive soils are abundant in arid and semi-arid regions around the
world, including Australia, Canada, China, South Africa, India and the United
States (Sharma and Sivapullaiah 2016). In the United States, these soils range from
the Gulf of Mexico to the Canadian border, and from Nebraska to the Pacific Coast
(Figure 2.13) (Nelson and Miller 1997). In the United States, Texas has the most
severe type of expansive soils, with high swell pressure (2000-8000 psf) and PI (30-
60 %) (Chen 2012). The expansive soils in Houston, Texas expand 10% after
rainfall. Conversely, during the drought season, they lose moisture and shrink, often
resulting in desiccation cracks. The swelling and shrinkage behaviors of expansive
soils are not completely reversible, and the recurring cracks on the ground do not
25
seal completely after rewetting, resulting in degradation of engineering properties
with each additional wetting and drying cycle (Jones and Jones 1987, Jones and
Jefferson 2012, Adem and Vanapalli 2015, Mohanty et al. 2016, Jamsawang et al.
2017). Therefore, expansive soils are regarded as an unstable construction material
due to their high potential for swelling and shrinkage, and they do not offer
adequate strength and stiffness properties required for supporting civil
infrastructures (Pedarla 2013, Soltani et al. 2018).
Figure 2.13 Expansive soil distribution throughout the United States (Witczak
1972)
2.4 Problems Caused by Expansive Soils
Due to the significant volume changes, expansive soils cause more severe
damage to structures, especially foundations, light structures, pavements, and
slopes than any other natural disaster (Jones and Holtz 1973, Nelson and Miller
26
1997, Puppala and Cerato 2009, Estabragh et al. 2015, Sharma and Sivapullaiah
2016, Yixian et al. 2016, Banerjee 2017, Shahbazi et al. 2017, James and Pandian
2018, Banerjee et al. 2018b, 2019, Puppala et al. 2019a). In Australia, major cities
are heavily affected by expansive soils (Kapitzke and Reeves 2000). It is reported
that the insurance companies in Australia provide compensation to owners of
approximately 50,000 houses that incur cracks caused by expansive soils per year
(Alazigha et al. 2018b). In the United States, expansive soil-related damage to
structures is estimated to range from $2 to $9 annually (Pedarla 2013), and it has
been reported that the annual cost of repairing homes and other infrastructures
exceeds $15 billion (Jones 1992, Al-Rawas and Goosen 2006, Shahbazi et al.
2017). Figure 2.14 shows the annual cost of damages caused by structures built on
expansive soils in the United States from 1973 to 2009; the total losses resulting
from expansive soil amounted to nearly $375 billion from 1973 to 2016 (Adem and
Vanapalli 2016). In the state of Texas alone, at least $1 billion is spent per year to
repair damaged houses, pavements, buried utilities, and embankments constructed
on expansive soils (Punthutaecha et al. 2006, He et al. 2018a).
27
Figure 2.14 The annual cost of damage to structures built on expansive soils in the
United States since 1973(Adem and Vanapalli 2016)
In summary, the problems associated with the presence of expansive soils
and its detrimental impact on the performance of overlying infrastructures are
primarily attributed to the excessive swell-shrink behavior. The swelling clays can
exert uplift pressures as much as 5,500 psf, which is enough to cause moderate
damage to structures and pavements (Rogers et al. 1993, James and Pandian 2016,
Sharma and Sivapullaiah 2016). Some case studies of engineering failures related
to expansive soils are listed below.
2.4.1 Pavement Failures
Expansive soils exhibit significant volume changes due to seasonal
moisture fluctuations, resulting in different types of stresses on the pavements built
over them (Wanyan et al. 2010, 2014, Dessouky et al. 2014). The pavements
undergo distresses such as cracking, settlement, and heaving due to the stresses
induced by the underlying expansive soil subgrade (Puppala et al. 2003, Djellali et
28
al. 2017). Different types of cracks emanate on the pavement surface built on
expansive soils, and expose the underlying layers to rain water (Figure 2.15)
(Pedarla 2013).
Among the different types of pavement cracks mentioned above,
longitudinal cracks (Figure 2.16) are the most commonly encountered on
pavements built on expansive soil subgrades in Texas (Wanyan et al. 2014). As the
cracks on the pavement can be extensive, it is essential to repair the pavements. The
annual cost for maintenance and rehabilitation of the pavements is estimated at
around $1 billion in the USA and $150 million in the UK (Djellali et al. 2017). In
order to mitigate the loss from failure of pavements built on expansive soils,
chemical stabilizers are frequently used to treat the expansive soil subgrades and
improve the engineering properties (Wanyan et al. 2010, Puppala et al. 2012).
29
Figure 2.15 Crack types on pavements built on expansive soils (Dafalla and
Shamrani 2011)
30
Figure 2.16 Longitudinal cracks in a road pavement in Texas (Zornberg and
Gupta 2009)
2.4.2 Foundation Failures
Swell pressure results in heave or uplift in humidifying climates, while
shrinkage leads to differential settlement in the drought season (Khademi and
Budiman 2016). Therefore, failure occurs when volume changes are unevenly
distributed underneath the ground. Figure 2.17 reflects cracks caused by expansive
soils on a building in northern Oman.
Drilled pier foundations have been widely used in California, Colorado, and
Texas since 1950 to mitigate the severe structural damage caused by expansive soil.
However, this type of foundation is not effective in resisting the high swelling
potential of expansive soils unless the pier is drilled to a sufficient depth beneath
the ground surface (Rogers et al. 1993). Figure 2.18 shows the progressive damage
caused to light structures during cyclic drought and rainfall seasons. The corner
31
piers are suddenly lifted because of the heave of swelling soil in the wet season, but
after the soil shrinks in the following dry season, the skin friction between the pier
and soil gradually decreases, and the piers fail to support the whole structure.
Although there are several ways to tackle this type of problem, the best way to
mitigate this type of damage is to extend the foundation underneath the active zone
in which moisture content fluctuates with seasonal variations. This ensures
sufficient skin friction adhesion to prevent uplift of the pier (Rogers et al. 1993,
Biswas and Ghosh 2019). Embankments built with expansive soils are also affected
significantly. The slopes of earth structures such as dams, levees, or highway
embankments experience rainfall-induced stability issues that affect the
serviceability of structures. This aspect is elucidated in detail in the next section.
Figure 2.17 Building foundation failure (Al-Rawas and Goosen 2006)
32
Figure 2.18 Damage to home supported on shallow piles (Rogers et al. 1993)
2.4.3 Slope Failures
The number of rainfall-induced slope failures has increased in the past 20
years due to global climate change, which has caused huge economic damage to
tropical regions (Leung and Ng 2016, Yang et al. 2016). During the wet season, the
increase in pore water pressure caused by rainfall directly influences the shear
strength of the soil (Cho and Lee 2002, Runqiu and Lizhou 2007). However, during
the drought season, the soil experiences desiccation cracking, which facilitates the
intrusion of water during the next rainfall. The reduced shear strength and the
hydrostatic pressure exerted by the cracks filled with rainwater result in slope
33
sliding (Pedarla 2013). Figure 2.19 shows two typical slope failures in Texas that
were primarily caused by the formation of desiccation cracks followed by a rainfall
event. Another type of slope failure, surficial failure, always takes place near
highways and railways (Xiao et al. 2018), and can be attributed to the swelling and
shrinkage of fissures during the wetting and drying cycles, which significantly
reduces the strength of the slope surface (McCook 2012).
In Section 2.4, different problems caused by expansive soils, including
damage to pavements, slopes, and earth structures are described, as are the various
chemical stabilizers utilized as preventatives. In Texas, lime is widely used to treat
slope and pavement failures by enhancing the shear strength of the slopes
(Sirivitmaitrie et al. 2008). Chemical stabilizers are introduced in the next chapter,
where their stabilization mechanisms are discussed.
（a）
34
(b)
Figure 2.19 (a) Grapevine dam surficial slope failure, (b) Randell lake slope
failure in North Texas
2.5 Brief Introduction of Soil Stabilizer And Its Stabilization Mechanism
2.5.1 General
Various soil treatment methods have been developed in the past decades to
prevent damage from expansive soils. Soil stabilizers can be primarily divided into
three groups: traditional stabilizers, non-traditional stabilizers, and by-product
stabilizers. Traditional stabilizers, including lime, cement and fly ash; and by-
product stabilizers such as coffee husk, rice husk ash, bagasse ash, blast furnace
slag, steel slag, lignosulfonate, cement kiln dust (CKD), lime kiln dust (LKD) have
been comprehensively researched, and their stabilization mechanisms have been
identified and summarized (Tingle et al. 2007, Little and Nair 2009, Pranav et al.
35
2012, Ashango and Patra 2016, Ferreira et al. 2016, Sharma and Sivapullaiah 2016,
Shahbazi et al. 2017, Alazigha et al. 2018b, James and Pandian 2018, Atahu et al.
2019). Non-traditional soil stabilizers include ions, geopolymers, and enzymes
(Tingle et al. 2007).
Up to now, non-traditional stabilizers have not been widely used in practice;
nor have they been well accepted by engineers due to the lack of extensive
published research studies and documentations that unanimously highlight post-
treatment improvements in engineering properties. Moreover, the stabilization
mechanisms are not as well understood as the traditional calcium-based stabilizers
(Rauch et al. 1993, 2002, Tingle et al. 2007, He et al. 2018a, 2018c). Detailed
information pertaining to different soils stabilizers is provided below.
2.5.2 Traditional Stabilizers
2.5.2.1 Lime Stabilizers
Lime has been used as a soil stabilizer in construction practice since 1924.
It was extensively used for road construction during the Second World War (Bell
1996). In 1969, TXDOT used nearly half-a-million tons of lime to treat highways
and foundations (Chen 2012). Over the past several decades, it has been proven that
lime treatment is an effective and economic solution for enhancing the engineering
properties and mitigating the detrimental effects of expansive soils on pavements,
embankments, slopes, and light structures (Elkady 2016, Wang et al. 2016,
Chakraborty and Nair 2018a, 2018b, Elkady and Shaker 2018). Lime stabilization
36
enhances the workability, strength, and permeability coefficient of soils, and
inhibits the swell-shrink behavior (Jones and Jones 1987, Pedarla et al. 2010, Al-
Taie et al. 2016, Belchior et al. 2017, Wang et al. 2017b, Nguyen et al. 2017,
Puppala et al. 2018b, Patil et al. 2018, Bhuvaneshwari et al. 2019, George et al.
2019a).
Several well-documented research studies are available that highlight the
fundamental mechanism behind lime stabilization. Typically, when lime is added
into the expansive soil, the primary reactions are hydration, cation exchange,
flocculation-agglomeration (Figure 2.20), and pozzolanic (Basma and Tuncer 1991,
Nelson and Miller 1997, Rajasekaran et al. 1997, Khattab et al. 2007, Wang et al.
2017b, Hotineanu et al. 2015, Wang et al. 2015, 2016, Elkady 2016, Elkady and
Shaker 2018, Bhuvaneshwari et al. 2019). When quicklime and water are mixed
with clay soil, the quicklime reacts with water to form hydrated lime or calcium
hydroxide (Wang et al. 2016). After hydration, the Ca2+ available from the lime is
attracted to the clay surface and dispels the water and other ions.
The PI of soil reduces significantly at this stage, and becomes friable and
workable, and can be easily compacted. This change in plasticity and texture of the
soil is attributed to cation exchange and flocculation and agglomeration, which lasts
several hours after mixing lime with soil (Rajasekaran et al. 1997, Chittoori 2008).
When enough lime and water are added to the soil and the pH value of the soil rises
over 10.5, the clay particles begin to dissociate along the edges of the clay particles
37
(Hotineanu et al. 2015, Elkady and Shaker 2018). The silica and alumina available
from the dissolution of the clay particles react with calcium from the lime to form
calcium-silicate-hydrate (C-S-H) and calcium-aluminate-hydrate (C-A-H)
(Chittoori 2008, Elkady and Shaker 2018). These cementitious gels are similar to
that formed during hydration of cement, which binds soil particles and improves
the strength and stiffness properties. As the pozzolanic reaction may continue for
months or years, the strength and stiffness of lime-treated soils continue to increase
with curing time (Elkady 2016, Wang et al. 2016, Elkady and Shaker 2018).
Figure 2.20 Flocculation and agglomeration (Prusinski and Bhattacharja 1999)
2.5.2.2 Cement Stabilizers
Cement is produced through a closely controlled chemical combination of
calcium, silicon, aluminum, iron and other ingredients. It has been widely used in
construction since 1915 (Little et al. 2000). Among traditional stabilizers such as
lime, cement, and fly ash, cement is most commonly used in ground improvement
projects built on fine-grained soil with low-to-medium plasticity due to its
38
effectiveness (Sirivitmaitrie et al. 2008, Horpibulsuk et al. 2010, Bahmani et al.
2014, Raftari et al. 2014, Sasanian and Newson 2014, Kumar and Janewoo 2016,
Mengue et al. 2017, Puppala et al. 2018b). When cement is mixed with soil, a
chemical reaction may occur between the calcium hydroxide and soluble silica and
aluminum in the clay, resulting in altering the clay structure and inhibiting the
swell-shrink behavior of the soil (Prusinski and Bhattacharja 1999, Chittoori 2008,
Raftari et al. 2014, Puppala 2016, Mengue et al. 2017, Wang et al. 2018). However,
due to the high purity of the calcium hydroxide produced in the hydration progress,
it reacts with clay minerals much faster than lime, so the cement provides a greater
increase in soil strength than lime in the initial period of time (Raftari et al. 2014,
Sasanian and Newson 2014).
Although cement has been proven effective in treating the low or medium
plasticity of expansive soil, it is not recommended for treating very high expansive
soil (PI>30) due to the difficulty of mixing the cement into the soil (Chittoori 2008,
Puppala 2008). In these cases, lime must be added to the soil to reduce the PI and
improve the workability of the soil prior to adding the cement (Hicks 2002).
Sirivitmaitrie et al., (2008) compared the lime treatment with treatment of a
combination of lime and cement on low-to-medium expansive subgrades. The
combined treatment enhanced the soil strength and stiffness (Figure 2.21), and
reduced the swell potential and plasticity index more than the lime-only treatment.
39
Figure 2.21 Comparison of resilient modulus for untreated, lime-treated and
cement-lime- treated soils at the deviator stress= 68.9 kPa (Puppala 2008)
2.5.2.3 Fly Ash Stabilizers
Fly ash is an industrial by-product generated from the combustion of coal
(Misra 1998, Senol et al. 2006, Ahmaruzzaman 2010). According to the United Soil
Classification System (USCS), it is a combination of silica, aluminum, iron oxides
and unoxidized carbon, and the gradation is similar to that of non-plastic silt (Cokca
2001, Zha et al. 2008). Compared to lime and cement, the major benefits of using
fly ash are its relatively cheap price and its propensity for reducing greenhouse
gases (Phanikumar and Sharma 2007, Göktepe et al. 2008, Tastan et al. 2011).
Two major types of fly ash, Class F and Class C, are available in the market.
Class F fly ash, which is produced from bituminous coal, does not contain an
40
appreciable CaO content, and hence is not self-cementing in nature (Cokca 2001,
Chittoori 2008). To meet the demands of strength and stiffness for designing a
pozzolanic-stabilized mixture (PSM) road base, a source of calcium, such as lime
or cement must be added (Little 1995). Class C fly ash is self-cementing, with 20
to 30 percent of CaO that is obtained from lower-sulfur coal (Cokca 2001). When
fly ash is added to soil in the presence of water, the exchangeable cations provided
by the fly ash, including Al3+, Ca2+ and Fe3+, result in flocculation of the soil
particles (Zha et al. 2008). The fly ash serves as a rich source of silica that reacts
with lime in a high pH environment to form the cementitious products. The
pozzolanic reaction in a soil-fly ash mixture occurs slower than a soil-cement, but
is much faster than lime-treated soil (Chittoori 2008).
Many researchers have revealed that the addition of fly ash to soil can
reduce the swell-shrink potential, plasticity, and permeability, as well as increase
the stiffness, strength, and durability of the treated soils (Misra, 1998; Cokca, 2001;
Nalbantoğlu, 2004; Phani Kumar and Sharma, 2004; Edil, Acosta and Benson,
2006; Li et al. 2008). Table 2.1 compares the process, effects, and application types
of lime, cement, and fly ash (Chittoori 2008).
41
Table 2.1 Comparison of Lime, Cement, and Fly Ash (Chittoori 2008)
2.5.3 By-product Stabilizers
Various industrial and agricultural by-products, including coffee husk, rice
husk ash, bagasse ash, blast furnace slag, steel slag, lignosulfonate, cement kiln
42
dust (CKD), and lime kiln dust (LKD) have gradually replaced traditional soil
stabilizers to improve soil properties and reduce the costs (Ashango and Patra 2016,
Kumar and Janewoo 2016, Sharma and Sivapullaiah 2016, Shahbazi et al. 2017,
Alazigha et al. 2018a, James and Pandian 2018, Atahu et al. 2019). As the majority
of the by-products are siliceous and calcareous materials, their primary stabilization
mechanisms are similar to traditional stabilizers, including pozzolanic and cation
exchange reactions (Kumar and Janewoo 2016, Alazigha et al. 2018b). Non-
traditional stabilizers include enzyme stabilizers, geopolymer stabilziers,
biopolymers and ionic stabilziers, which are introduced below (Caballero et al.
2016).
2.5.3.1 Enzyme Stabilizers
An enzyme is defined as an organic catalyst that accelerates chemical
reactions in the soil (Rajoria and Kaur 2014, Malko et al. 2015, Gupta et al. 2017,
Thomas et al. 2018). It is an eco-friendly alternative soil stabilizer that is fermented
from vegetable extracts and effectively increases soil strength and stiffness (Tingle
et al. 2007, Rajoria and Kaur 2014, Das et al. 2016, Gupta et al. 2017, Gheytaspour
and Bigdarvish 2018, Sterpi et al. 2018, Habibzadeh-Bigdarvish et al. 2019, Lei et
al. 2019). The application of enzyme stabilization can be traced back to 1981, when
it was successfully utilized to treat a half-mile of pavement in Oklahoma (Renjith
et al. 2017). However, the effectiveness of the enzyme for treating problematic soils
is still questionable.
43
The stabilization mechanism of enzymes can be explained by the positively
charged enzyme-encapsulated organic molecules, which enable them to be attracted
to the net negative surface charge of clay minerals (Scholen 1992, Marasteanu et
al. 2005). The organic molecules that surround the clay minerals balance the
negative charge, and reduce the clay’s affinity for water (Figure 2.22) (Tingle et al.
2007, Rajoria and Kaur 2014, Gupta et al. 2017).
Several case studies indicate that enzyme stabilization is only effective for
treating specific soils (Tingle et al. 2007), with the researchers claiming that
enzyme additives fail to treat granular soils (Santoni et al. 2005). Minor changes
were observed in the XRD results for clays in the Texas region before and after
enzyme treatment (Rauch et al. 1993). It is recommended that enzymes be used to
treat soils with a clay content from 12% to 24 % and plasticity index from 8% to
35% (Kestler 2009). In summary, the stabilization mechanism of enzymes is still
in dispute, but it may not be effective for treating all expansive clay soils.
Figure 2.22 Proposed enzyme stabilization mechanism (Tingle et al. 2007)
44
2.5.3.2 Geopolymer Stabilizers
Geopolymer is an inorganic material that is synthesized by the
polymerization of silica and alumina tetrahedra (Zhang et al. 2013, 2015,
Phummiphan et al. 2016). It is regarded as an environmentally friendly alternative
soil stabilizer for treating expansive soils, and imparts high compressive strength
and low shrinkage and swell potentials in pavements and light structures (Samuel
et al. 2019). However, the descriptions of the stabilization mechanism of
Geopolymer stabilizers are conflicted in literature. Some research studies espouse
that Geopolymer stabilizers are typically suspended in an emulsion by surfactants,
and the soil strength is improved via physical bonding when the polymer coats the
soil particles (Rauch et al. 1993, Tingle et al. 2007).
Other studies infer that the cations of polymer are attracted to the negative
charges on the clay surface, leading to neutralization of the charge and a subsequent
reduction in affinity for water (Iyengar et al. 2012). The strength of silty sand
treated with polymer after 28 days was significantly increased (Santoni et al. 2005);
moreover, the Si/Al molar ratio influenced the effect of the polymer. Soil properties
were improved significantly when the Si/Al ratio was in the range 1-3 and the Na/Al
molar ratio was around 1 (Khadka et al. 2018).
2.5.3.3 Ionic Stabilizers
Ionic soil stabilizers are divided into two groups: acids and alkaline (Tingle
et al. 2007). Due to their low cost and simple construction, they have been regarded
45
as an alternative soil stabilizer for reinforcing clay soil (Katz et al. 2001, Cui et al.
2011). Scholen (1992) stabilized expansive soils with ionic stabilizers and indicated
that liquid ionic soil stabilizers (LISS) cause cation exchange and clay mineral
flocculation. Ionic stabilizers change the molecular structure via dissipating the
double-layer water film and flocculating the soil particles in the progress of the
reaction, as shown in Figure 2.23. This stabilization mechanism would be suitable
for Montmorillonites, where the double-layer water is much larger than the clay
particle size (Tingle et al. 2007).
A study by Rauch et al. (2002) showed a significant reduction in plasticity
property after sodium Montmorillonite was treated with an ionic soil stabilizer. The
chemical reaction was found to make the clay structure much more stable and to
dispel the excess double-layer water. The mechanism of stabilization using LISS
has also been attributed to the reduction of the cation-exchange capacity, decrease
in the thickness of double-layer water, and changes in the density of the electrical
charge of clay particle surfaces (Liu et al. 2009). LISS is an electrolyte that
dissolves in water. The strong cations of LISS can exchange with the cations of the
clay particle surface (Xiang et al. 2010), and the anions are able to impair the
surface tension of the water film. The absorbed water then easily becomes free
water, changing the soil from hydrophilicity to hydrophobicity (Figure 2.24).
Ali (2012) claimed that some strong cations, such as potassium (K+) and
magnesium (Mg2+), can replace weaker cations, such as H+, to satisfy the
46
unbalanced negative charge on the clay particles. This kind of replacement reduces
clay’s affinity for water, making it less susceptible to absorbing water, and leads to
better soil particle interlocking that results in enhanced dry density and improved
shear strength. Recently, an environmentally friendly product of LISS, hydrogen
ion exchange chemical treatment (HIEC), which is mainly composed of sulfuric
acid, was used to treat the expansive subgrades of Texas. The HIEC was diluted
with water before mixing it with soils. The treatment of the soil with HIEC caused
an electrochemical reaction, which broke the water bonding effect and reduced the
swell-shrink behavior of the soil. The proper stabilization mechanism of HIEC
might be attributed to the reduced negative charge on clay minerals that occurred
via releasing the aluminum atoms present in the interlayer of clay minerals, thereby
inhibiting the water molecules attracted to the clay (Hariharan et al. 2018).
Figure 2.23 Proposed stabilization mechanisms of ionic soil stabilizer (Tingle et
al. 2007)
47
Figure 2.24 Model of ionic soils stabilizer reducing water film (Xiang et al. 2010)
2.5.4 Comparison of Traditional Stabilizers and Non-traditional Stabilizers
Due to cation exchange, followed by flocculation and agglomeration,
traditional soil stabilizers effectively improve soil strength, workability, and
stiffness, as well as control its swell-shrinkage behavior (Zhang et al. 2013, Puppala
et al. 2014b, Hariharan et al. 2018, Khadka et al. 2018). However, due to the
formation of ettringite, which occurs when the sulfate in soils reacts with alumina
and silica in a high pH environment (Puppala et al. 2014), excessive heaving occurs
in sulfate-rich regions treated by traditional stabilizers (Sherwood 1962, Mitchell
and Dermatas 1992, Kota et al. 1996, Puppala and Musenda 2000, Puppala et al.
2012). The ettringite could easily expand up to 250% when coming in contact with
water (Adams et al. 2008). In addition, a large quantity of carbon dioxide is emitted
to the atmosphere during the production of traditional stabilizers, which
exacerbates the greenhouse effect (Zhang et al. 2015, He et al. 2018b).
As non-traditional soil stabilizers are calcium-free products, they are
effective for treating high-sulfate soils (Tingle et al. 2007, Xiang et al. 2010, Cui et
48
al. 2011, Wang and Liu 2011, Iyengar et al. 2012, Alhassan and Olaniyi 2013,
Zhang et al. 2015, Malko et al. 2015, Gupta et al. 2017, He et al. 2018c, 2018b,
2018a, Thomas and Yadu 2018). Most non-traditional soil stabilizers are provided
as concentrated liquids, are diluted with water in the field, and then injected deep
into the soil layers (Rauch et al. 2002, Jones and Jefferson 2012). The primary
benefit of non-traditional stabilizers is the low transportation cost of the additive
for field treatment application (Katz et al. 2001). An enzyme stabilizer is regarded
as an effective soil stabilizer due to its positive treatment outcome, low cost, and
simple application (Gupta et al. 2017). Unlike Geopolymer and enzyme stabilizers
that might only be effective to treat specific soils, LISS is an alternative stabilizer
that can be used to treat expansive soils without any restrictions. Hence, one kind
of LISS was selected to treat expansive soils in this study. Previous studies related
to LISS treatment are summarized in Section 2.6
2.6 Effect of LISS on the Soil per Previous Studies
LISS is regarded as an alternative stabilizer for treating expansive soil.
Previous studies related to the LISS treatment of expansive soils and subsequent
improvements in different engineering properties such as Consistency Limits,
moisture-density relationship, UCS, and volume change test are summarized in this
section. However, the content for each test was too limited, some tests results were
conflicted and inconvincible, and the stabilization mechanisms of LISS were not
clearly explained, making it difficult for engineers to accept and practice LISS
49
treatment (Liu et al. 2009, Cui et al. 2011, Wang and Liu 2011, He et al. 2018a,
Zhang et al. 2018). Therefore, it is essential to carry out a series of tests, including
physical-chemical tests, engineering tests, and microstructural tests. The
stabilization mechanism of LISS and detailed information derived from
comprehensive tests before and after treatment will be discussed in the next
chapters.
2.7 Summary
This chapter introduced expansive soil as clay soil that undergoes a
significant volume change when it comes in contact with water. The distribution of
expansive soil in the United States; the swell-shrinkage behavior of expansive soil
during drought and wet seasons; and the problems caused by expansive soil to
pavements, foundations, and slopes are discussed. Three primary clay minerals,
Illite, kaolinite, and Montmorillonite, and their clay structure and characteristics
were briefly introduced. Of the three clay minerals, Montmorillonite has the
greatest swell potential.
Soil stabilizers have been used in past decades to prevent losses incurred by
damages to infrastructures caused by expansive soil. The concept and stabilization
mechanisms of traditional soil stabilizers, by-product stabilizers, and non-
traditional stabilizers were listed in this chapter, and their advantages and
disadvantages were compared. This study focuses on LISS. The limited literature
review of LISS treatment of expansive soils was summarized, including a soil pH
50
test, Consistency Limits, moisture-density relationship, UCS, RM test, volume
change test, and microstructural test. The stabilization mechanisms of LISS are not
clearly described in the literature, and some of the test results are conflicted.
Therefore, a series of comprehensive laboratory tests were carried out in this
dissertation study to evaluate the optimum dosage ratio of LISS, as well as to
understand LISS’s stabilization mechanisms.
51
Chapter 3
EXPERIMENT PROGRAM
3.1 Introduction
In this study, a commercially available Liquid Ionic Soil Stabilizer, LISS,
was used to treat two expansive soils from Dallas and Carrollton, Texas. The
stabilizer is mainly composed of sulfuric acid, phosphoric acid, citric acid, water,
and surfactant (Figure 3.1). According to the description provided from the
manufacturer, it is a non-toxic and environmentally friendly alternative soils
stabilizer that has shown promising results and has been used effectively to treat
expansive soils in Texas. Treating soil with LISS decreases the potential vertical
rise by 50% within a year of treatment.
In the field, the LISS additive is diluted with water and then pressure-
injected into the ground to mix and treat the soil (Figure 3.2). The dilution ratio
suggested by the manufacturer is 8 gals of the chemical concentrate to 340 g of
surfactant with 6,000 gals of water. Surfactant is regarded as the secondary
additives in LISS. It changes the surface charges on the clay particles, which
reduces the surfwotension of the pore fluid (Tingle et al. 2007).
At the site, the five perforated rods are hydraulically pressed 6 inches into
the ground, and the solution is injected at a rate of 100 gals per minute to complete
the chemical pass in approximately 12 seconds. At the end of the first pass, the rods
are further penetrated 6 inches, and the pressure injection process is repeated. For
52
residential buildings in Texas, this process is typically continued until the top 10 ft.
of the soil layer has been treated with LISS.
In the laboratory, the field application ratio recommended by manufacturer
was carried out by mixing 5 ml of concentrated LISS and 0.057 g of surfactant with
1 gal of water. Two other dilution ratios were also selected to assess the degree to
which the LISS dosage improved the engineering properties of problematic soil
(Table 3.1).
To avoid the influence of fertilizers and plant roots, all of the bulk soils were
collected after the top 3 ft. of the soil was removed from the ground surface. The
soils were classified as highly plastic clay (CH) as per the Unified Soil
Classification System (USCS) (Table 3.2) and were found to be suitable candidates
for chemical stabilization. Treated soil samples were prepared by hand mixing dry
soil with LISS solutions at the respective optimum moisture content (OMC). A
series of laboratory tests were conducted to comprehensively study the effect of
LISS on the problematic soil and comprehend the probable stabilization mechanism.
The research works were conducted in four major steps:
(1) Physical, chemical, and microstructural tests on untreated and LISS-treated
specimens;
(2) Engineering tests on untreated and LISS-treated specimens;
(3) Assessment of stabilization mechanism;
53
(4) Numerical modeling to assess the applicability of using LISS to stabilize a slope
which had incurred a surficial failure, and to enhance the design life of a road built
on a problematic subgrade soil.
Figure 3.1 LISS: Concentration liquid chemical and surfactant
Figure 3.2 Deep injection rake for pressurized injection of LISS (Source:
http://www.prochemtex.com/Services.html)
54
Table 3.1 Three LISS Ratios Considered for Soil Treatment Studies
LISS Proportion
(Chemical/Water)
First Ratio
(5 ml/gallon)
Second Ratio
(2.5 ml/gallon)
Third Ratio
(10 ml/gallon)
Chemical Concentrate (ml) 5 5 10
Surfactant (g) 0.057 0.057 0.114
Water (gallon) 1 2 1
Figure 3.3 presents a flow chart of the major research tasks performed in
this study. A summary of the laboratory procedures followed, and an introduction
of the equipment used are presented in this chapter.
Figure 3.3 Flowchart for the research tasks
55
3.2 Physical, Chemical and Microstructural Studies of Test Soils
A series of physical and chemical tests was performed on the control soils
and LISS-treated soils to characterize and comprehend the behavior of the soil
before and after treatment. The tests were performed on the treated soils, after
varying curing periods, to observe the time-dependent changes in the properties.
Physical tests included the hydrometer analysis, specific gravity, Consistency
Limits, and standard compaction tests. The cation exchange capacity (CEC), total
potassium (TP), specific surface area (SSA), and pH were evaluated as a part of the
chemical tests. The results of the microstructural tests (SEM, XRD, and EDS), both
before and after treatment, were analyzed to identify the modifications experienced
by the clay particles when treated with LISS. The details of the different tests
performed during this research study are explained in detail in the following
sections.
3.2.1 Physical Tests
The physical tests included basic soil characterization tests, such as specific
gravity, grain size distribution, consistency limit, and standard compaction. These
tests provided the basic soil properties.
3.2.1.1 Specific Gravity and Grain Size Distribution Tests
The specific gravity of soil solids (Gs) is defined as the mass of a unit
volume of soil solids to the mass of the same volume of gas-free distilled water at
20º C and was determined in accordance with ASTM D854. As the two candidate
56
soils belong to CH (Table 3.2), the grain size distribution test was determined using
wet sieve analysis as per ASTM D1140. The same procedure was used to measure
the grain size distribution for treated soil to detect whether the reaction products
could bind the clay particles. The detailed information is listed in section 3.4.3.
3.2.1.2 Consistency Limits Tests
Consistency Limits, Including liquid limit (LL) and plastic limit (PL),
provide information on the effect of moisture content on the mechanical properties
of soil (Kalinski 2011). The LL tests of soil before and after treatment were carried
out as per ASTM D4318-17. After the LL test, the wet samples were air dried to
reach the plastic limit (PL) state. An E-180 PL rolling device (Figure 3.4), initially
developed by the Texas Department of Transportation, was used to measure the PL
of untreated and treated soils (Tex-105-E). The consistency limits of the treated
soils were also determined after various curing periods, so that changes in soil
plasticity properties could be observed. They are discussed in Section 3.4.4.
Figure 3.4 The E-180 plastic limit rolling device (He et al. 2018a)
57
3.2.1.3 Standard Proctor Compaction Tests
A standard Proctor compaction test determines the relationship between
OMC and maximum dry density (MDD) (Das 2002). The standard compaction test
of untreated soils was carried out as per ASTM D698. For treated soils, at least 1.8
kg of pulverized dry soils were mixed with different dilution ratios of LISS in
separate containers. The moist soil specimens were kept in the moisture room the
night before the Proctor test in order to allow proper moisture equilibration. This
also allowed adequate time for chemical reactions between the liquid chemicals and
the soil before compaction testing. All of the samples in this research were prepared
at OMC and 95% MDD for engineering tests listed in Figure 3.3. Table 3.2
summarizes the physical test of control soils.
Table 3.2 Physical Test for Control Soils
Soil Properties Dallas Soil Carrollton Soil
Liquid Limit, LL (%)
(ASTM D4318) 76 73
Plastic Index, PI (%)
(ASTM D4318) 58 48
Specific Gravity, Gs
(ASTM D854) 2.84 2.71
Maximum Dry Density,
(MDD) (pcf) 85.7 96.5
Optimum Moisture Content
(OMC) (%)
(ASTM D698)
31.0 23.0
USCS Classification CH CH
% Clay Fraction
(ASTM D1140) 40 11
58
3.2.2 Chemical Tests
Chemical tests include the CEC, TP, SSA, and pH tests, which indicate the
clay mineralogy and the progressive chemical reaction between the soil and LISS.
3.2.2.1 Clay Mineralogy Measurement of Soil
The three major clay minerals are Illite, kaolinite, and Montmorillonite. The
percentage of each mineral was determined based on correlations among SSA, TP,
and CEC, established by Chittoori (Chittoori 2008, Chittoori and Puppala 2011,
Gautam 2018). The related formulas are listed below. M, K, and I are
Montmorillonite, kaolinite, and Illite, respectively.
Table 3.4 displays the clay mineralogy content of the two candidate soils.
The procedures of CEC, TP, and SSA are shown in Figure 3.5, Figure 3.6, and
Figure 3.7, respectively. Table 3.3 shows the results of the mineralogical tests
performed on the two test soils;
Table 3.4 displays the clay mineralogy content of the two soils.
%𝑀 = −2.87 + 0.08 ∗ 𝑆𝑆𝐴 + 0.26 ∗ 𝐶𝐸𝐶 (3.1)
%𝐼 = [𝑇𝑃
6] ∗ 100 (3.2)
%𝐾 = 100 −%𝐼 −%𝑀 (3.3)
Table 3.3 Mineralogical Tests Performed on Two Soils
Soil CEC (meq/100g) TP (%) SSA (m2/g)
Dallas 163.5 1.0 197
Carrollton 120.7 2.06 181
59
Table 3.4 Clay Mineralogy Contents of Two Soils
Soil Montmorillonite (%) Illite (%) Kaolinite (%)
Dallas 55.4 27.1 17.4
Carrollton 52 14 34
Figure 3.5 Flowchart of detailed procedures for CEC (Gautam 2018)
60
Figure 3.6 Flow chart of determining TP in the soil (Chittoori 2008)
61
Figure 3.7 Flow chart for the SSA test (Chittoori 2008)
62
3.2.2.2 pH Test
The pH test results may provide understanding of the long-term impact of
LISS on the environment, and its suitability to be used as a stabilizer. They were
carried out according to ASTM D4972. Approximately 300 grams of soil were
completely submerged in the LISS for curing periods of 1, 7, 14, 21, and 28 days.
The pH of the supernatant liquid was monitored at the end of each curing period to
study the variations of pH due to progressive chemical reactions. Figure 3.8 shows
the device used for testing for the pH of soil.
Figure 3.8 pH test device
3.2.3 Microstructural Tests
Microstructural tests are composed of Field Emission Scanning Electron
Microscope (FESEM), Energy Dispersive X-Ray Spectroscopy (EDS), and X-Ray
Powder Diffraction (XRD). This test provided understanding of the interactions
63
between the soil and LISS additive, and morphology changes before and after LISS
treatment.
3.2.3.1 Field Emission Scanning Electron Microscope (FESEM) Test
FESEM study was used to study the microstructural changes in clay
particles before and after treating the soil with LISS. A sample prepared by the low
temperature-dry suspension liquid method was used in this research to observe the
morphological changes. Approximately 250 g of pulverized dry soil was soaked in
1 liter of a chemical solution for one month. The suspended liquid was filtered and
then placed in the oven at a low temperature.
In order to enhance the quality of images, a CRC-100 sputtering machine
(Figure 3.9) was used to coat the samples with silver. The samples were placed on
the aluminum stub uniformly by using double-sided carbon tape. The coating
process generally took around 3 minutes at the pressure of 5 to 10 millitorr when
the chamber was full of argon gas.
The Hitachi S-4800 II FESEM (Figure 3.10) was used to obtain images for
control and treated specimens. The morphological changes were monitored from
similar images to detect any reaction product formed due to LISS treatment.
64
Figure 3.9 CRC-100 sputtering machine
c
Figure 3.10 Hitachi S-4800N variable pressure FESEM
65
3.2.3.2 Energy Dispersive X-ray Spectroscopy (EDS)
Energy dispersive spectroscopy was used in conjunction with FESEM
imaging to identify the chemical composition of the reaction products identified in
the SEM images. In this study, the Hitachi S-3000N variable pressure SEM-EDS
machine was used (Figure 3.11). The peak intensity of common elements in the
clay soil, such as calcium, aluminum, potassium, silicon, sulphur, and magnesium
were monitored before and after treatment. In addition, aluminum-to-silica ratios
were analyzed to determine the change in the silicon ratio, which could partially
explain the difference in the strength and stiffness of the untreated and treated soil
(Rauch et al. 1993, 2002, Katz et al. 2001),.
Figure 3.11 Hitachi S-3000N SEM-EDS
3.2.3.3 Powder X-ray Diffraction (XRD) Analysis
XRD enabled qualitative identification of clay minerals in the control soils
66
and facilitated the assessment of changes in clay mineralogy due to LISS treatment.
The location of the peaks obtained from XRD was compared to known mineral
powder diffractograms for Montmorillonite, Observations of the changes in the
relative intensity of the peaks and the presence of new additional peaks initially
absent in the untreated soil are useful in identifying the formation of stabilization
products in the treated soil specimens. A Bruker D8 x-ray diffractometer was used
for the XRD analysis (Figure 3.12).
The samples for powder XRD were ground and pulverized to a fine
homogeneous powder. The specimen was scanned through a 2θ range of 10° to 90°
at the scanning speed of 0.01 degree per second. The diffraction peaks were
collected at an acceleration voltage of 40kV, with a current of 40mA. The Cu Kα
radiation, with a wavelength of 1.5406 A°, was used for the XRD analysis. Match
3 software was utilized to analyze the soil XRD patterns from a crystallographic
database before and after treatment. The information obtained from FESEM-EDS
and XRD was used to identify the reaction products and predict the probable
stabilization mechanism formed in the LISS-treated the soil.
67
Figure 3.12 Bruker D8 x-ray diffractometer machine
3.3 Engineering Tests
This section presents a detailed description of the methodology and purpose
of the individual tests conducted to evaluate improvement in the engineering
properties of the LISS-treated soils. Each of the soils was treated with three
different LISS dosages, and the specimens were prepared at the respective target
optimum moisture content (OMC) and compacted to 95% of maximum dry density
(MDD), to simulate the field conditions. The soil was uniformly hand mixed with
a liquid chemical stabilizer and then stored overnight in a 100% humidity controlled
room for mellowing and equilibration. After compaction, the soil specimen were
cured for varying time periods in the moisture room. Replicates of the sample were
prepared for the different types of tests to avoid drawing erroneous conclusions.
Unconfined compressive strength (UCS) and resilient modulus (MR) were
performed on the control and LISS-treated samples, after which they were cured
68
for varying times, to evaluate the time-dependent improvements in strength and
resilient moduli properties. Swelling and shrinkage related volume change tests
were performed to evaluate the reduction in the soil’s affinity for water after
treatment with LISS. Direct shear tests were performed on soils to assess the shear
strength properties of soils before and after LISS treatment. The details of the
individual tests, along with their applications, are elucidated in the following
sections.
3.3.1 Unconfined Compressive Strength (UCS) Tests
The UCS test on the soils was performed before and after treatment
according to ASTM D 2166. The purpose of this test was to obtain the unconfined
compressive strength of the soil at constant shearing rate of 0.1 in./min (Banerjee
and Puppala 2015). For control samples, soils were mixed with water and
immediately prepared through a static compaction machine. Treated soil samples
were uniformly mixed with different dilution ratios of liquid chemicals, and then
kept in a 100% humidity-controlled room overnight to allow chemical reactions
between the soil and stabilizer. After compaction, soil specimens were cured in the
moisture room for 7 days and 28 days, respectively. The unconfined compressive
strength of control and treated specimens, prepared at various dilution ratios, were
evaluated to judge the effectiveness of LISS in terms of increase in unconfined
compressive strength with curing time. All of the specimens were tested on a
Geocomp triaxial machine (Figure 3.13).
69
Figure 3.13 Geocomp triaxial machine
3.3.2 Resilient Modulus (MR) Tests
Resilient modulus tests on untreated and treated soils were conducted
according to AASHTO T307 method. The test includes 15 stress sequences of
repeated load testing at various confining pressures. Each of the sequence was
performed at an unique confining pressure and deviator stress. During the test, each
loading cycle was comprised of 0.1 sec of haversine load pulse followed by 0.9 s
of the relaxation period. Each sequence consisted of 100 cycles, the mean value of
the resilient modulus was however calculated from the determination of resilient
strains of the reloading curve for the last five cycles of each loading sequence
(Buchanan 2007, Banerjee 2017, Bhuvaneshwari et al. 2019, George et al. 2019a).
The relationship between the resilient modulus (MR) and the deviator stress during
each test sequence was analyzed for both untreated and treated soils that had been
70
cured 7 days and 28 days, respectively. Comparisons provided the effects of LISS
on the resilient moduli of soils.
The resilient modulus values of control and treated samples, prepared at
different dilution ratios, were evaluated after various curing periods, to study the
impact of curing time on the performance of the stabilized soils. Figure 3.14 shows
the resilient modulus test equipment used in the laboratory tests.
The relationship between the UCS and MR results were also analyzed to
generate ready-to-use correlation equations similar to the universal model used in
the literature. The universal model is suitable for soils varying from cohesive to
non-cohesive, and was utilized to analyze the relationships among resilient
modulus, bulk stress, shear stress, and elastic moduli of soil (George 2004). This
model provided an engineer to design the pavements in a realistic manner (Han and
Vanapalli 2015).
Figure 3.14 Resilient modulus test setup
71
3.3.3 1-D Swell Test
The purpose of 1-D swell test is to provide an understanding of the affinity
of soil for water before and after treatment. The 1-D swell test was performed in
accordance with ASTM D 4546 via the conventional oedometer apparatus (Figure
3.15). The soil specimens were obtained by statically compressing wet mixed soil
samples to achieve their optimum compaction state. All treated specimens were
kept in the moisture room for 7 or 28 days. During the swell tests, the specimens
were completely soaked in the oedometer, with an initial seating load of 1 psi or 7
kPa for at least 48 hours. A dial gauge was put on the loading frame to monitor the
vertical displacement during water absorption. The swell potential for control and
treated specimens prepared at different dilution ratios were analyzed. The swell test
results of the treated specimens provided an understanding of soil’s affinity for
holding water molecules around the soil particles.
Figure 3.15 1-D Swell test setup
72
3.3.4 Fatigue of Swelling Test
The effect of swell-shrink behavior on pavements built on expansive soils
was observed to be insignificant after a couple of years of wetting and drying cycles
(Chen 2012). The treated samples were allowed to swell completely in the
oedometer, then were air-dried to their initial moisture content, before being put
them back into the oedometer to undergo swelling again. This repeated swell and
drying process, which is called fatigue of swelling, was performed to simulate the
long-term swell-shrinkage behavior of expansive soil in the field condition.
The fatigue of swelling test provided an in-depth understanding of the effect
of ingress and egress of water into the LISS-treated soil and its impact on the
overlying structure. The optimum treatment dosage was assessed, based on the
fatigue of swelling test results in conjunction with the observed gain in strength and
stiffness with curing time.
3.3.5 Linear Shrinkage Strain Test
In general, swelling and shrinkage of expansive soils are interrelated;
however, whether high swelling soils indicate corresponding high shrinkage is still
uncertain. Linear shrinkage bar tests were performed on untreated and treated
samples to quantify the shrinkage potential of the soil as per Tex-107-E. The
pulverized soil was mixed with water or LISS until the liquid limit. Then the wet
soils were transferred into the linear bar mode and gently vibrated to allow the soil
flow, as well as eliminate the bubbles (Figure 3.16). After the molds were fully
73
filled, the sample was exposed to air for approximately five hours, and then oven-
dried at 110 ºC. The linear shrinkage ratio was determined to evaluate the
effectiveness of LISS treatment. Additionally, the results were compared with the
swell potential to understand swell-shrinkage interdependency of LISS-treated
soils.
Figure 3.16 Linear shrinkage bar test setup
3.3.6 Direct Shear Test
The direct shear test was performed in accordance with ASTM D 4546. It
provided the shear strength properties of soils including soil cohesion and friction
angle under conditions of drained loading, which were later used to assess the
stability of earthen embankment slopes. The soil specimens were obtained by
statically compressing wet mixed soil samples to achieve their optimum
74
compaction state. All treated specimens were kept in the moisture room for 7 or 28
days.
3.4 Assessment of Stabilization Mechanisms
A series of tests which included monitoring (a) changes in pH, (b) variations
in water content, (c) shifts in grain-size distribution patterns from hydrometer
analysis, and (d) changes in Consistency Limits with curing time were performed
on the soil samples treated by the third ratio. These tests, in conjunction with the
microanalysis studies, provided insight into the short-term and progressive
chemical reactions which may have resulted in the formation of new reaction
products. An attempt was made to justify the observed changes in engineering
properties, based on the above-mentioned test results, and gain some understanding
of the probable reaction mechanism.
3.4.1 Variations in pH
The primary purpose of the pH tests was to gain some understanding of the
extent of the chemical reactions between soil particles and LISS. A variation in pH
with curing time indicated a progressive chemical reaction and formation of new
reaction products, which might explain the improvement in engineering properties
reported in the available literature review. The rate of change in pH with curing
time (1, 7, 14, 21, and 20 days) might also act as a surrogate measure of the reaction
rate. The rate of chemical reaction, along with the rate of strength gain, was used
to judge the efficacy of the different treatment concentrations of LISS. Available
75
literature and brochures of LISS manufacturing companies suggested that one of
the biggest advantages of LISS is its environmental-friendly nature (Katz et al.
2001, Rauch et al. 2002, He et al. 2018a). The pH test results provided more
understanding of the long-term impact of LISS on the environment and its
suitability to be used as a stabilizer.
3.4.2 Variations in Moisture Content
The variations in water content of the treated soils with curing time
supported the hypothesis of the formation of new reaction products that used up
some portion of the mixing water that was initially used to prepare the sample.
Oven-drying the soil specimen at 110°C for 24 hours could only remove the loosely
bound water present in the macropores of the soil. The chemically bound water,
which might be used for the formation of the new reaction products, was not
removed at 110°C in 24 hours. Hence a reduction in available water implied the
utilization of water for the formation of reaction products. The variations in water
content, along with the changes in pH values, supported the progressive chemical
reaction and led to the improvements in engineering properties.
Approximately 500 grams of soil were mixed with LISS at OMC and stored
in Ziploc bags for curing periods of 1, 7, 14, 21, and 28 days. The moisture content
was recorded at the end of each curing time. The variations of water content with
curing time provided information on the formation of reaction products that require
water for hydration.
76
3.4.3 Variations in Consistency Limits for Treated Soils
Consistency Limits of the treated soils were determined after various curing
periods to observe changes in plasticity. The observed changes in PL, LL, and PI
provided some additional information on the soils’ affinity for water, and it was
observed that PI and LL values can indirectly reflect the soil’s swell potential before
and after treatment. The decrease in PI and LL values were generally associated
with a reduction in the potential for swelling and water absorption. The variations
of PI and LL values with curing time were related to the changes in the soils’ swell
potential after treatment. The results were utilized to judge the efficacy of LISS
with various dilution ratios.
Consistency Limits was determined as per ASTM D4318. Approximately
500 grams of soil were mixed with LISS until optimum moisture content, after
which they were stored in Ziploc bags and cured for 1, 7, 14, 21, and 28 days. The
Consistency Limits reading was recorded at the end of each curing time. Since the
liquid limit and the swelling of clays both depend on the amount of water that clay
tries to absorb, it is not surprising that the Consistency Limits can indicate the
swelling behavior of clays. The Consistency limit results provided insight into the
swelling behavior of LISS-streated soils.
3.5 Numerical Modeling
Two case studies were selected to assess the suitability of implementing LISS
treatment as a viable option for treating soils with lower engineering properties. A
77
typical failed slope in North Texas was considered for this task. The stability analysis
was performed using a commercially available two-dimensional finite-element-
based software package to study the improvement in the stability of the embankment
after treating the surficial slopes with LISS. The embankment was modeled using the
material properties (cohesion and friction angle) corresponding to untreated soils and
LISS-treated soils. The global factor of safety was compared before and after
treatment to evaluate the efficacy of stabilizing problematic soils with LISS.
Flexible Pavement Design System (FPS21) software was later utilized to
analyze the design life of a road hypothetical scenario where LISS treated soil was
used as one of the base layers. The subgrade soil properties of control and treated
soils were used as input parameters to the software package. The cracking life and
rutting life were calculated and compared before and after treatment to evaluate the
pavement design age of treated soil section.
3.6 Summary
The progress of in-situ LISS treatment and basic soil properties performed
on three expansive soils were presented in this chapter, as were a series of
engineering tests that were utilized to determine the soil strength, stiffness, and
volumetric behavior. Chemical tests on soils indicated the mineral content of
expansive soils. The volumetric behavior of compacted soil samples was
determined via fatigue of swelling, 1-D swell, and swell pressure. The strength and
stiffness of expansive soils were measured by performing UCS, and resilient
78
modulustests. The detailed procedures of these tests are described in this chapter.
Advanced techniques such as SEM, EDS and XRD that were utilized to study
morphology changes in expansive soils before and after the tests, along with their
working principles, were discussed.
The stabilization mechanism was assessed, based on the above tests and
additional variation tests in the field of pH, moisture content, grain-size distribution
of treated soil, and Consistency Limits. Details of the tests are provided. Two case
studies of slopes and pavements were selected for judging the suitability of
implementing the LISS treatment. The next chapter deals with the test results
obtained from a comprehensive test listed in this chapter.
79
Chapter 4
THE EFFECT OF LISS ON PHYSICAL AND ENGINEERING PROPERTIES
OF EXPANSIVE SOILS
4.1 Introduction
The limited amount of literature on the subject related to LISS treatment of
soils and unclear stabilization mechanisms prompted the research to address this
topic. Hence, in the current research, a series of comprehensive tests, including
physical and engineering tests, were carried out to evaluate the effectiveness of
LISS treatment on different expansive soils. Details of the test procedures and
working principles were described in Chapter 3. The results of two tests performed
on expansive soils, before and after treatment, are presented in this Chapter.
4.2 Physical Tests
4.2.1 Standard Compaction Test
The test results of the standard Proctor compaction curve are presented in
Figure 4.1. In treated soil, chemical reactions between the soil particles and the
LISS additive tend to happen prior to compaction, which causes soil particle
flocculation. From the figures, it can be seen that the MDD of all of the soils
reduced, while the OMC increased. The decrease in MDD can be attributed the
specific gravity of the LISS-treated soil being lower than that of the expansive soil
(Sweeney et al. 1988). The increase in OMC can be attributed to the chemical
reactions between LISS and the soils that consume extra water (He et al. 2018a).
80
(a)
(b)
Figure 4.1 Standard Compaction Curve for Expansive Soils Before and after
Treatment. (a) Dallas Soil. (b) Carrollton Soil
81
4.2.2 Consistency Limits Tests
Test results of the consistency limits of two expansive soils are presented in
Table 4. 1. The liquid limit (LL), plastic limit (PL), and plastic index (PI) of all
twosoils are similar, before and after LISS treatment. In addition, LL, PL, and PI
are indirect parameters that indicate moisture affinity changes in the engineering
properties of soils, and provide estimates of the soil swell potential (Chen 2012).
These features of expansive soils, before and after treatment, are discussed in the
following sections. The LISS treatment is not very effective at reducing the
consistency limits of expansive soils.
Table 4. 1 Three LISS ratios for Consistency Limits on two expansive soils
Dallas Soil
ISS Concentration to Water (ml/gallon) LL (%) PL (%) PI (%)
0 (Untreated) 76 18 58
2.5 (Second Ratio) 72 15 57
5 (First Ratio) 79 29 50
10 (Third Ratio) 74 19 55
Carrollton Soil
ISS Concentration to Water (ml/gallon) LL (%) PL (%) PI (%)
0 (Untreated) 73 25 48
2.5 (Second Ratio) 72 22 50
5 (First Ratio) 73 18 55
10 (Third Ratio) 70 25 42
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4.3 Engineering Tests
4.3.1 Unconfined Compressive Strength (UCS) Test
Unconfined compressive strength tests were performed on the untreated and
LISS-treated soil samples, using three different dilution ratios. For the Dallas and
Carrollton soils, two specimens were prepared for each stabilizer ratio, to avoid
erroneous results.
4.3.1.1 Dallas Soil
The UCS values of the Dallas soil, before and after treatment with various
LISS dosages, are shown in Figure 4.2. As the OMC and MDD values were almost
the same for the control samples and samples treated by the first ratio from the
standard compaction curve, the compressive strength of the soil before and after
treatment was very similar. The mean maximum strength dropped slightly, to 13
psi, for the second ratio, even though the specimen was kept in the moisture room
for 28 days due to OMC being higher and MDD being lower than those of the
untreated samples. In the third ratio, the mean compressive strength of the control
and treated samples, cured after 7 days and 28 days, were 16 psi, 24 psi, and 28 psi,
respectively. Although the MDD of the soil samples treated by the third ratio was
slightly less than that of the control sample, the vertical compressive strength
boosted to 75% after chemical treatment and curing for 28 days, which can be
attributed to the soil flocculation after chemical treatment. In addition, an increase
in curing time resulted in higher compressive strength after treatment, due to a
83
continuous chemical reaction between the soil and LISS stabilizer (Sweeney et al.
1988, He et al. 2018a).
(a)
(b)
84
(c)
(d)
Figure 4.2 UCS Test Results of Dallas Soil. (a) Dallas Soil-First Ratio Treatment.
(b) Dallas Soil-Second Ratio Treatment. (c) Dallas Soil-Third Ratio Treatment.
(d) Effect of LISS Dosages and Curing Time on UCS
85
4.3.1.2 Carrollton Soil
The UCS values of the Carrollton soil, before and after treatment with
various LISS dosages, are listed in Figure 4.3. The first ratio OMC of treated soils
(27%), was larger than that of the original samples (24.5%), and the MDD of treated
soils (90 pcf) was less than that of the control samples (97 pcf). The test results
showed that the strength value rose almost 30% after treatment, due to the chemical
reaction between LISS and the soil, and the curing time had a slight impact on the
Carrollton soil that was treated by the first ratio. The mean compressive strength of
the samples treated with the second ratio and cured after 7 days and 28 days, was
47 psi and 58 psi, which boosted the unconfined compressive strengths by 7% and
32%, respectively. This was due to the OMC (23%) being lower than that of the
control sample. As the OMC and LISS content of the soil treated with the first ratio
was higher than that of soil treated with the second ratio, and the MDDs were being
close and similar, the compressive strength of the soil treated by the second ratio
was close to the strength of the soil treated by the first ratio. The vertical strength
of the soil treated by the third ratio and cured for 7 days and 28 days, was 45 psi
and 55 psi, respectively, because of the high LISS content. These results represent
moderate improvements in the soil’s UCS values (25% increment for treated soil
cured for 28 days).
86
(a)
(b)
87
(c)
(d)
Figure 4.3 UCS test results of Carrollton soil. (a) Carrollton Soil-First Ratio
Treatment. (b) Carrollton Soil-Second Ratio Treatment. (c) Carrollton Soil-Third
Ratio Treatment. (d) Effect of LISS dosages and curing time on UCS
88
4.3.1.3 Summary
The UCS values are highly dependent on the soil type, LISS content, OMC,
and MDD conditions. Among all of the parameters, the LISS content has the biggest
impact on the compressive strength of expansive soils, and the treated soils were
stronger than the control soils. The longer curing time also enhanced the
compressive strength.
4.3.2 Repeated Load Triaxial Test (RLT) to Determine Resilient Modulus (MR)
RLT tests of untreated and treated samples were conducted according to
AASHTO T307 (Rahman and Tarefder 2015). Table 4.2 presents the resilient
moduli of Dallas and Carrollton soils before and after treatment. The MR values
were influenced by LISS dosages, OMC, and MDD of soil. In general, samples
compacted at high density have a higher resilient modulus than those compacted at
low density. If samples are prepared with a higher OMC, their resilient modulus
normally reduces (Mohammad et al. 1995, Puppala and Hanchanloet 1999,
Chakraborty et al. 2017, Banerjee et al. 2018a, 2019, He et al. 2018c, George et al.
2019c). In Dallas soils, although the LISS content in the third ratio is higher than
the first ratio, the MR value of the first ratio was found to be slightly higher than
that of the soils prepared at the third ratio. This may be due to relatively lower OMC
and higher MDD of first ratio as compared with those of third ratio.
For the second ratio dosage, as the OMC of treated soil was larger than that
of other treated soils, and the MDD of treated soil was less than that of treated soil
89
by first ratio or third ratio, the MR value of the second ratio was less than that of the
other two ratios. The MR value of treated soil using three different dosages, after
curing for 28 days, was improved at least 43% due to the soil flocculation after
treatment in section 5.2.1.
For Carrollton soils, the MDD of all of the treated soils was nearly the same
for all of the dilution dosages; however, the OMC of the soils treated with the
second ratio (22.5%) was less than that required for treating the soil with the first
ratio (27.5%). The soils treated with the third ratio exhibited the highest OMC value
(32%). Despite the higher LISS contained in the third ratio compared with that in
first ratio, MR of the soils treated with the third ratio was still lower than that
required for treating the soil with the first ratio. Among the three dilution ratios
used in this study, the soils treated with the second ratio exhibited the highest MR
due to lowest OMC content. To some extent, the treated soils, after being cured for
28 days, exhibited 90% to 180% higher resilient moduli as compared with control
samples.
90
Table 4.2 Resilient Modulus of soils before and after treatment. (a) Dallas soil (b) Carrollton Soil
Confining
Pressure
(kPa)
Deviator
Stress
(kPa)
Control Dallas-Curing 7 days Dallas-Curing 28 days
MR (MPa)
MR (MPa) MR (MPa)
First
Ratio
Second
Ratio
Third
Ratio First Ratio
Second
Ratio
Third
Ratio
41.4 12.5 44.5 91.1 39.2 53.8 84.6 68.0 63.7
41.4 25.1 45.6 85.5 39.1 51.5 80.5 63.9 60.4
41.4 37.6 43.7 81.2 35.5 49.0 77.2 60.4 57.1
41.4 49.9 41.6 77.7 32.0 46.7 74.8 57.8 54.7
41.4 62.7 39.4 74.6 28.7 44.6 72.5 54.4 51.8
27.6 12.6 44.7 86.2 37.0 50.7 81.6 64.9 61.3
27.6 25.2 44.0 82.6 34.3 48.7 77.8 61.7 58.1
27.6 37.6 42.3 78.3 31.4 46.5 75.5 58.6 54.9
27.6 50.1 40.3 75.8 29.2 44.9 72.4 56.3 52.9
27.6 62.2 38.5 73.7 27.5 43.3 71.4 54.0 50.9
13.8 12.5 40.8 81.4 33.7 47.9 77.3 63.1 58.6
13.8 25.2 40.8 78.8 30.8 46.1 71.7 60.0 55.6
13.8 37.7 39.4 75.8 28.8 44.2 70.1 57.5 53.1
13.8 50.2 37.9 73.6 27.1 43.0 69.2 55.2 51.3
13.8 62.6 36.7 71.8 25.9 41.7 67.7 52.9 49.5
(a)
91
Confining
Pressure
(kPa)
Deviator
Stress
(kPa)
Control Carrollton-Curing 7 days Carrollton-Curing 28 days
MR (MPa)
MR (MPa) MR (MPa)
First Ratio Second
Ratio
Third
Ratio First Ratio
Second
Ratio
Third
Ratio
41.4 12.7 36.3 69.6 39.2 67.6 86.9 102.4 68.9
41.4 24.9 42.0 71.5 40.4 74.2 79.7 103.4 75.7
41.4 37.1 49.8 71.9 44.6 75.5 76.9 99.6 75.4
41.4 49.5 57.5 71.1 65.4 75.5 76 97.1 73.9
41.4 62.1 72.7 69.7 75.8 74.8 72.3 96.0 72.4
27.6 13.0 35.1 75.9 47.0 51.0 81.1 110.9 76.3
27.6 25.4 43.8 72.8 57.6 63.2 76.9 103.3 73.7
27.6 37.6 55.8 70.4 65.4 67.6 74.1 98.1 71
27.6 49.8 63.3 68.4 71.4 68.7 72 94.2 69.5
27.6 62.0 69.6 67.4 75.9 69.7 69.7 92.3 68.5
13.8 12.5 33.5 71 54.8 56.2 74.8 102.6 69.6
13.8 24.9 44.8 68.1 63.6 61.3 71.6 96.9 66
13.8 37.8 56.1 66.2 67.7 62.1 69.5 93.7 64.1
13.8 49.8 64.1 64.9 69.9 62.2 67.8 91.1 63.4
13.8 62.0 70.0 63.9 71.9 63.4 67.3 89.0 63.2
(b)
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4.3.3 Universal Model for Predicting Mr Value
The universal model was developed on the basis of the bulk stress created
by Uzan (1985). In this model, the octahedral stress was substituted for the deviator
stress, which explains the stress state of the material (George 2004).
32
1 1
kk
octr a
a a
M k PP P
= +
(4.1)
The model constants, k1, k2, and k3 are coefficients that depend on the
material type and physical properties. Pa is the atmospheric pressure. is the bulk
stress, oct is the octahedral shear stress, k1 is proportional to Young’s modulus, and
k2 indicates the soil stiffness or hardening of the material. A regression analysis of
the expansive soils before and after treatment, and the regression coefficient are
summarized below.
4.3.3.1 Dallas Soil
Figure 4.4 reflects the regression analysis of the resilient modulus of Dallas
soil before and after chemical treatment. Table 4.3 summarizes all of the regression
coefficients and coefficients of determination values.
93
(a) Control soil
(b) First ratio-7 days (c) First ratio-28 days
(d) Second ratio-7 days (e) Second ratio-28 days
94
(f) Third ratio-7 days (g) Third ratio-28 days
Figure 4.4 Resilient Modulus of Dallas soil before and after treatment
Table 4.3 Dallas Soil-Regression coefficients of resilient modulus and coefficient
determination before and after treatment
k1 k2 k3 R2
Control 469.11 0.1278 -0.9712 0.9152
First Ratio 914.03 0.0999 -1.0427 0.9868
7 days
First Ratio 854.13 0.1504 -1.0330 0.9687
28 days
Second Ratio 423.06 0.2295 -2.0311 0.9641
7 days
Second Ratio 692.89 0.0711 -1.1302 0.9921
28 days
Third Ratio 543.97 0.1287 -1.1195 0.9935
7 days
Third Ratio 651.49 0.0865 -1.1562 0.9955
28 days
4.3.3.2 Carrollton Soil
Figure 4.5 reflects the regression analysis of the resilient modulus of
95
Carrollton soil before and after chemical treatment. Table 4.4 summarizes all of the
regression coefficients and coefficients of determination values.
(a) Control soil
(b) First ratio-7 days (c) First ratio-28 days
96
(d) Second ratio-7 days (e) Second ratio-28 days
(f) Second ratio-7 days (g) Second ratio-28 days
Figure 4.5 Resilient Modulus of Carrollton soil before and after treatment
97
Table 4.4 Carrollton Soil-Regression coefficients of resilient modulus and
coefficient determination before and after treatment
k1 k2 k3 R2
Control 285.35 -0.0204 3.6540 0.974
First Ratio 744.68 0.0741 -0.5528 0.6162
7 days
First Ratio 854.13 0.1504 -1.0330 0.9687
28 days
Second Ratio 367.49 -0.3354 3.2118 0.8031
7 days
Second Ratio 1094.99 0.0692 -0.8207 0.8169
28 days
Third Ratio 607.85 0.2337 0.2742 0.7363
7 days
Third Ratio 752.52 0.1474 -0.6390 0.6166
28 days
The majority of the resilient moduli results, and analyses showed that k1 and
k2 are positive. However, some k3 is negative, as the increasing deviatoric or shear
stress appear to soften the material. In addition, in most cases, k1 and k2 values of
treated soils are greater than those of untreated soil, due to the higher strength and
stiffness of soils after treatment.
4.3.4 Linear Shrinkage Test
Linear shrinkage bar tests are performed on expansive soils before and after
treatment to quantify their shrinkage limits. Table 4.5 illustrates the test results of
two expansive soils. A slight difference of shrinkage potential can be observed
among the samples of the control soil and the soil that was treated with various
98
dosages. Hence, it seems that LISS proven to be less effective in inhibiting the
shrinkage potential.
Table 4.5 Three LISS Ratios for Consistency Limits of Two Expansive Soils
Dallas Soil
LISS Concentration to Water (ml/gallon) Average Linear Shrinkage (%)
0 (Untreated) 22
2.5 (Second Ratio) 24
5 (First Ratio) 23
10 (Third Ratio) 23
Carrollton Soil
LISS Concentration to Water (ml/gallon) Average Linear Shrinkage (%)
0 (Untreated) 16
2.5 (Second Ratio) 15
5 (First Ratio) 16
10 (Third Ratio) 14
4.3.5 One-Dimensional Swell Test
One-dimensional swell tests were performed on untreated soil and soil
treated by three different dilution ratios. Figure 4.6 and Figure 4.7summarize the
swell potential of Dallas and Carrollton soils, respectively. The swell potential
reduced significantly after treatment in both soils. Furthermore, a longer curing
time and LISS dosages had a positive effect on inhibiting the swelling behavior of
the expansive soils. The swell potential of the Dallas soil treated by the third ratio
after curing 28 days reduced almost 90%, compared with the untreated specimen.
The swell potential of the original Carrollton soil was 7.6%, while that of the
Carrollton soil treated with the third ratio dropped to 3.5% after being cured for 28
days. In terms of the results listed above, it can be stated that the double chemical
99
ratio of LISS is most effective among all dilution ratios in reducing the soil swelling
potential.
(a)
(b)
100
(c)
Figure 4.6 Swell potential of Dallas soil. (a) Dallas Soil-First Ratio Treatment. (b)
Dallas Soil-Second Ratio Treatment. (c) Dallas Soil-Third Ratio Treatment
(a)
101
(b)
(c)
Figure 4.7 Swell potential of Carrollton soil. (a) Carrollton Soil-First Ratio
Treatment. (b) Carrollton Soil-Second Ratio Treatment. (c) Carrollton Soil-Third
Ratio Treatment
102
4.3.6 Fatigue of Swelling Test
Figure 4.8 displays the fatigue of swelling test for treated Dallas and
Carrollton soils that were cured for 7 days to allow enough time for the chemical
reactions between the soil and LISS to occur. After the drying-wetting cycles were
repeated several times, over a period of at least three weeks, the swelling trend
became smooth and reached a stable condition.
As Montmorillonite is 2:1 phyllosilicate, the bonding between the tops of
the silica sheet is weak, resulting in the water and exchangeable ions easily
separating the basic layers, which attracts more water (Holtz and Kovacs 1981).
Although the Montmorillonite content of Dallas soil is very similar with that of
Carrollton soil, the OMC of Carrollton soil is much less than that of Dallas soil,
which may explain why the Carrollton soil has a slightly larger potential for
swelling than the Dallas soil. Overall, it can be concluded that LISS is helpful in
controlling the swell potential of soil during long-term drying-wetting cycles.
103
(a)
(b)
Figure 4.8 Fatigue of swelling. (a) Dallas Soil. (b) Carrollton Soil
104
4.4 Summary
The comprehensive evaluation of test results from the physical and
engineering tests listed above showed that the expansive soils treated with the
double chemical ratio experienced increase in soil strength and resilient modulus,
as well as a decrease in the swell potential. The stabilization mechanism of LISS
was assessed by chemical and microstructure tests that are described in the next
chapter.
Because of these improvements, two case studies, one on slope treatment
and another utilizing a treated base to support pavements, were formulated and
analyzed to determine the benefits of using LISS (double chemical ratio) treated
soils.
105
Chapter 5
STABILIZATION MECHANSIMS OF LISS TREATMENT
ON EXPANSIVE SOILS
5.1 General
This chapter presents the mechanisms most probably responsible for the
improvement in engineering properties of the expansive soils treated with liquid
ionic soil stabilizers. While the previous chapter focused on analyzing the test
results from a macro level, this chapter presents the possible reason(s) behind the
observed improvements, which are primarily based on microstructural test results.
As mentioned in Chapter 4, the third ratio was found to be the most effective dosage
for treating expansive soils. This stabilizer dosage enhanced the soils’ strength and
stiffness and reduced the swell potential significantly. Therefore, an attempt was
made to predict the probable stabilization mechanism(s) of LISS treatment of
expansive soils, based on different physical, chemical, and microstructural tests
performed on untreated soils and soils treated with the third ratio only.
5.2 Microstructural Tests
Microstructural tests that were performed to gain an in-depth understanding
of the fundamental reaction mechanisms and these tests and studies include
FESEM, EDS, and XRD methods. These test results were analyzed to identify the
chemical reaction products formed in LISS-treated soil that may have enhanced the
probable stabilization mechanisms.
106
5.2.1 Field Emission Scanning Electron Microscope (FESEM) Test
In this study, FESEM imaging was used to study the microstructural
changes of control and treated soils, namely Dallas soil and Carrollton soil. The
FESEM images for both the treated and untreated soils were obtained at 10k
magnification, and these images are presented in Figure 5.1 and Figure 5.2. Unlike
the control soil, a stark difference in morphology can be observed after the soil was
treated. The individual clay particles present in the untreated soil are not visible in
the treated soil (Figure 5.1b and Figure 5.2b). Instead, the FESEM images indicate
the presence of abundant flaky reaction products and fused clay particles, and this
binding of the clay particles may contribute towards imparting higher strength and
stiffness in the treated soils. A similar phenomenon was also observed and
documented by Zhang et al. (2015). The probable elemental composition of the
flaky products that were observed to bind the clay particles together (Figure 5.3)
was determined through EDS, and the results are presented in the next section.
107
(a)
(b)
Figure 5.1 FESEM images of Dallas soil. (a) control sample. (b) treated sample
after 28 days
108
(a)
(b)
Figure 5.2 FESEM of Carrollton soil. (a) control sample. (b) treated sample after
28 days
109
Figure 5.3 The FESEM sideview image of expansive soil after treatment
5.2.2 Energy Dispersive X-Ray Spectroscopy (EDS) Tests
The EDS tests were performed and analyzed to evaluate the changes in the
elemental composition of the soil specimens, before and after treatment. As clay
minerals are composed of silicon tetrahedron and aluminum octahedron layers, the
reaction of the clay particles with LISS was expected to affect the Al:Si ratio after
treatment, due to the preferential dissolution of a particular layer in a low pH
environment (Figure 5.4). Hence the Al:Si ratios before and after treatment were
compared to gain an in-depth understanding of the possible reaction mechanism
between LISS and clay particles (Rauch et al. 1993). From the FESEM images of
the treated sample, a cluster of clay particles can be observed to be bound by a layer
of the reaction product (Figure 5.3). Hence, the Al/Si ratio was analyzed, both for
110
the reaction product formed at the surface and the underlying clay particles (Figure
5.3).
Figure 5.4 The effect of a high pH system is to release silica and aluminum from
the clay surface (Little 1995)
Table 5.1 shows the Al/Si ratio of clay particles for Dallas and Carrollton
soils before and after treatment. As LISS is an acid-based stabilizer (Section 5.3.2),
part of the aluminate layer of clay particles dissolved in the LISS, thereby reducing
the Al/Si ratio after treatment. This is in agreement with the observations made by
Rauch et al. (1993). The Al/Si ratio of the Dallas soil reduced by 28%, while that
of the Carrollton soil decreased by 16%, indicating the greater extent of chemical
reaction between LISS and the Dallas soil as compared to the Carrollton soil.
Hence, the post-treatment improvement in engineering properties in the Dallas soil
was more pronounced than in the Carrollton soil in terms of increase in strength
111
(Figure 4.2 in Section 4.3.1) and decrease in swell potential (Figure 4.7 Section
4.3.6).
Table 5.2 presents the Al/Si ratio of the reaction products observed in the
FESEM images of treated Dallas and Carrollton soil specimens. The Al/Si ratio of
the binding product formed at the surface was higher than that present in the clay
particles after treatment. This indicates the utilization of the Al3+ that dissolved
from the clay particles to form the new products, which partially supports the
observations made by Rauch (1993) (Section 5.2.1). Besides using FESEM and
EDS results to detect the formation of new compounds after LISS treatment, X-ray
diffractograms were also analyzed to further support the hypothesized stabilization
mechanisms.
Table 5.1 Al/Si ratio change for Dallas and Carrollton soil before and after
treatment
Soil Type Al: Si (clay particle)
Control Sample Third Ratio after 28 days
Dallas 0.402 0.291
Carrollton 0.384 0.324
Table 5.2 Al/Si ratio change for Dallas and Carrollton surface reaction products
after treatment
Soil Type Al: Si (reaction products)
Control Sample Third Ratio after 28 days
Dallas 0.402 0.426
Carrollton 0.384 0.376
112
5.2.3 Powder X-Ray Diffraction (XRD) Test
Figure 5.5 shows the XRD analyses results for control and treated samples
of Dallas soil and Carrollton soil, respectively. Different clay minerals, such as
quartz, kaolinite, Illite, and Montmorillonite, along with some new reaction
products that formed, were identified and studied before and after treatment. In the
X-Ray diffractograms, the clay minerals, quartz, and new reaction products are
denoted by letters C, Q, and R, respectively.
In Dallas soil, the quartz peak at 26 2ϴ and the Montmorillonite peak at 68
2ϴ reduced in the diffractogram of the treated soil, while new peaks appeared at 15
2ϴ, 23 2ϴ, 31 2ϴ, and 33 2ϴ, indicating the presence of new chemical products
that formed after treatment (Figure 5.5a). A similar reduction in clay mineral peaks
and the presence of new peaks corresponding to reaction products can be observed
for the Carrollton soil (Figure 5.5b).
The EDS data provided in Section 5.2.2 indicated a reduction in the Al/Si
ratio of the clay particles after treatment, due to dissolution of the alumina layer in
the low pH environment. As phosphoric acid is one of the main ingredients of LISS,
the alumina layers in clay will inevitably react with it to produce an aluminum
phosphate phase. It was reported by Moorlag in 2000 that monaluminum phosphate
(Al(H2PO4)3) initially forms at a low temperature, and the Al(H2PO4)3 continues to
react with the excess aluminum in the solution to form aluminum orthophosphates
(AlO4P) under dry conditions (100 ℃) (Moorlag 2000).
113
The AlO4P peaks (marked as ‘R’) can be observed in the XRD
diffractograms of treated soils presented in Figure 5.5. This further supports the
hypothesis about the formation of aluminum phosphate/aluminum orthophosphate
phases in LISS treated soil specimens. Aluminum phosphate/aluminum
orthophosphate phases were also observed in the FESEM images of treated soils,
which is similar to the observations made by Lee et al. (2017). Aluminum
orthophosphates are known to exhibit characteristics that contribute to binding and
strength. Hence, the formation of these phases in LISS-treated specimens resulted
in an increase in the UCS and resilient modulus of the treated samples, as presented
in Section 4.3.1 (Chung 2003).
In summary, the analyses of different microstructural test results
highlighted (i) the modifications in morphology observed in the FESEM images,
(ii) the changes in the Al/Si ratio evident from EDS data, (iii) the decrease in
intensity of XRD peaks of clay minerals, and (iv) the presence of new XRD peaks
initially absent in the untreated soil specimen, and provided ample evidence that
the stabilization mechanism is probably responsible for the improvement of the
engineering properties of LISS-treated soils. These microstructural test results
indicated the fusion of clay particles when exposed to LISS, and the formation of
new compounds such as aluminum phosphates/orthophosphates, predominantly
formed by chemicals reacting with the aluminate sheet present in the clay particles.
114
The fused clay particles, along with the formation of binding reaction products, aid
in the improvement of engineering properties of problematic expansive soils.
(a)
(b)
Figure 5.5 XRD analysis of expansive soils. (a) Dallas soil. (b) Carrollton soil
115
5.3 Additional Tests
In addition to the microstructural tests mentioned above, some additional
physical and chemical tests were also performed to verify the LISS stabilization
mechanism. These additional tests included monitoring (a) changes in water
content, (b) variations of pH, (c) shifts in the grain size distribution pattern, and (d)
changes in the Consistency Limits with curing time. These tests, in conjunction
with the microanalysis studies, provided insight into the short-term and progressive
chemical reactions in LISS-treated soils.
5.3.1 Changes in Water Content
Oven drying a specimen at 110 ºC for 48 hours can remove the water held
in the pores of the soil but cannot remove the water used for the formation of
chemical reaction products. Therefore, a reduction in water content indicates that
water was utilized for the chemical reactions between the soil and LISS. The
variations in the water content of Dallas and Carrollton soils after treatment are
shown in Figure 5.6. After 25 days, the moisture content of the Dallas soil dropped
4.5%, while the moisture content of the Carrollton soil reduced 1.2%. As the
variation in the moisture content of Dallas soil was larger than that of the Carrollton
soil, the extent of progressive chemical reactions in the Dallas soil was higher than
that in the Carrollton soil. This supports the greater increase in unconfined
compressive strength of the treated Dallas soil, as compared to the Carrollton soil
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(section 4.3.1), which is in consonance with the inference drawn from the EDS data
(presented in Section 5.2.2).
(a)
(b)
Figure 5.6 Variation of moisture content after third ratio treatment. (a) Dallas soil.
(b) Carrollton soil
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5.3.2 Variation of pH
In addition to the variations in water content, Figure 5.7 and Figure 5.8 show
the variations of the pH with increased curing time. As LISS is an acid-based soil
stabilizer, the pH of the solutions was around 3 when the soils were soaked in LISS.
The pH of the Dallas soil dramatically increased from 3.25 to 5.5 in the first 5 hours,
and then gradually increased to 7.5 in 20 days. Although the pH of the Carrollton
soil increased very slowly in the first 5 hours, it gradually increased to 7.8 after 20
days. The increments of pH after treatment can be attributed to the chemical
reactions between the soil and LISS.
Acid-based stabilizers initially provide abundant H+ ions to the soil-water
system and create a low pH environment (≈ 3) around the clay particles. The
negative charge of the clay particles attracts these H+ ions by an electrostatic force
of attraction. The removal of H+ ions from the system leads to an immediate
increase in the pH within a few hours of the treatment, as observed in Figure 5.7a
and Figure 5.8a. Even though the pH increased with curing time in both the soils,
the rate of change in the Dallas soil’s pH was significantly higher than that of the
Carrollton soil, especially in the early stages of curing (within 5 hours). This can
be attributed to the higher Montmorillonite and Illite contents of the Dallas soil, as
compared to the Carrollton soil (Table 3.4). The high Montmorillonite content, SSA,
and CEC of the Dallas soil suggests the presence of higher negative surface charges
that immediately attracted and held H+ ions available from LISS and led to an
118
increase in the pH of the solution within 5 hours (Section 4.2). Furthermore, the pH
of the solution quickly rose to 6 in 5 hours, and gradually increased to 7.8 in 20
days, indicating that LISS can be an environmentally friendly soil stabilizer.
(a)
(b)
Figure 5.7 Variation of pH after the third ratio treatment. (a) Dallas soil (48
hours). (b) Dallas soil (20 days)
119
(a)
(b)
Figure 5.8 Variation of pH after the third ratio treatment. (a) Carrollton soil (48
hours). (b) Carrollton soil (20 days)
120
5.3.3 Variation in Consistency Limits
Table 5.3 reflects the variations in consistency limits with curing time for
Dallas and Carrollton soil after treatment. The post-treatment LL, PL, and PI
remained almost the same with increased curing time, which is in agreement with
the consistency limits provided in Section 4.2.2. Unlike lime-treated soils, the
texture of clay soils after LISS treatment was very similar to that of the control soils
(Figure 5.9).
Since the H+ ions are readily available in the clay-water system in LISS-
treated soils, the negatively charged clay particles attract the H+ ions, instead of the
polar water molecules, due to a strong electrostatic force of attraction. This
phenomenon may be responsible for the reduction in the swell potential of LISS-
treated soils. However, the small size and low valency of H+ ions, as compared to
the Ca2+, does not facilitate significant flocculation or agglomeration of clay
particles around the H+ ions. Subsequently, there is no appreciable change in the
texture of the soil or its consistency limits after treatment.
121
Figure 5.9 The texture change of expansive soil before and after treatment
Table 5.3 Variation in Consistency Limits with curing time
Dallas Soil
Curing Time (days) LL (%) PL (%) PI (%)
0 74 19 55
7 75 22 53
14 75 18 57
21 76 18 58
28 74 17 57
Carrollton Soil
Curing Time (days) LL (%) PL (%) PI (%)
0 70 25 42
7 68 22 46
14 71 24 46
21 73 28 45
28 71 27 44
5.4 Probable Stabilization Mechanisms
Based on the physical, chemical, and microstructural tests performed on
untreated and LISS-treated soil specimens, the following mechanisms are
122
considered responsible for the improvements in engineering properties of
problematic expansive soils.
• The dilution of LISS in water provides ample H+ ions in the solution. The
initial pH close to 3 suggests the presence of 10-3 moles/l of H+ ions in the
diluted solution. These H+ ions are the only cations provided by the LISS,
which when added to the soil, adhere to the negatively charged clay
particles, thereby reducing the moisture affinity of the clay particles.
• Since the H+ ions are readily available in the clay-water system, the clay
particles attract the H+ ions, instead of the polar water molecules, due to a
strong electrostatic force of attraction. This phenomenon may be
responsible for the reduction in the swell potential of LISS-treated soils.
The removal of the H+ ions from the liquid phase leads to an increase in the
pH of the solution within a few hours of treatment.
• Even though the swell potential was observed to drop immediately after
treating the soil with LISS, there was no appreciable change in the
consistency limits, as observed in the case of soil treated with different
calcium-based stabilizers. This can be attributed to the small size and low
valency of H+ ions, as compared to the Ca2+, which did not facilitate
significant flocculation and agglomeration of clay particles around the H+
ions. Subsequently, there was no appreciable change in the texture of the
soil or its consistency limits after treatment.
123
• The LISS provides a low pH environment around the clay particles, which
facilitates preferential dissolution of the aluminate layer, as compared to the
silicate layer present in the clay minerals. The available Al3+ reacts with the
other ingredients present in the LISS to form a flaky substance (Figure 5.1a
and Figure 5.2a) that binds the clustered and fused clay particles, thereby
imparting strength and stiffness to the treated soil. The exact chemical
composition of the reaction products may be aluminum orthophosphophate.
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Chapter 6
CASE STUDIES AND MODELING
The effects of the enhancement of mechanical properties of LISS-treated
soils are demonstrated by considering two hypothetical cases, for which pavement
design and slope stability analyses was performed. This helps in evaluating the
feasibility of implementing LISS treatment as an alternative option for stabilizing
expansive soils, which was considered in this study.
6.1 Pavement Design - Case Study
Flexible pavement design systems (FPS21) was utilized to analyze the
design life of pavement located in Venus, Texas (Figure 6.1) by incorporating LISS
treated subgrade as a subbase layer. The subgrade soil properties from Dallas soil
and Carrollton soil before and after treatment with a curing time of 28 days was
used as the input parameters for the analysis. Pavement failure occurs when the
asphalt surface fails to hold the original shape and issues are caused by developed
material stress (Djellali et al. 2017). The main issues including fatigue cracking and
permanent deformation are compared before and after treatment to evaluate the
pavement design life (Huang 1993).
125
Figure 6.1 Pavement location (1311 FM 1807, Venus, Texas)
Two parameters such as horizontal tensile strain (εt) at the bottom of the
asphalt layer and the vertical compressive strain (εv) at the top of subgrade layer
are critical for design purpose (Behiry 2012). The fatigue cracking of flexible
pavement is caused by horizontal tensile strain. The failure criteria are related to
the allowable number of load repetitions and the tensile strain. The permanent
deformation or rut dept along the wheel paths result in rutting cracks on the surface
of flexible pavement. The limit of rutting should be controlled under the tolerated
amount (0.5 inches) (Huang 1993).
In general, the fatigue failure model and rutting failure model are expressed
as
32
1 1
ff
f tN f E −−
= (6.1)
( ) 5
4
f
rN f
−
= (6.2)
126
Nf is the allowable number of load repetitions to prevent fatigue cracking.
Nr is the allowable number of load repetition to prevent rutting crack. E1 is the
elastic modulus of the asphalt layer. And f1, f2, f3 are constants determined from
laboratory fatigue test while f4 and f5 are constants determined from road tests.
These constants values vary with material type, environment, traffic conditions, and
the failure limits provided by different organizations including Asphalt Institute,
Research Laboratory (Huang 1993, Carpenter 2006). In this study, values of f1,f2,f3,
f4 and f5 are suggested as 0.0796, 3.291, 0.854, 1.365×10-9 and 4.477 by the Asphalt
Institute respectively (Institute 1982), which are often adopted by Texas Asphalt
Pavement Association (TXAPA).
Table 6.1 and Table 6.2 summarizes the properties of untreated soils and
treated soils curing 28 days of Dallas and Carrollton soils. The moisture unit weight
of subgrade soils before and after treatment are calculated from the standard
compaction curve in section 4.2.1. The resilient modulus of subgrade soils before
and after treatment were back-calculated via universal model (section 4.3.3)
(Buchanan 2007). Table 6.3 summarizes the pavement life of flexible base built on
the Dallas and Carrollton soils before and after treatment, respectively. The
pavement life of flexible base on subgrade Dallas soil after treatment (7.5 years) is
20% more than that of the control sample (6.3 years). The pavement life of flexible
base on subgrade Carrollton soil after treatment (8.5 year) increase nearly 50%
compared with control Carrollton soil (5.8 year) shown in Figure 6.2. As the
127
increase in resilient modulus of subgrade Carrollton soil (74%) far outweigh that of
Dallas soil (50%) (section 4.3.2), the rutting life increment of the flexible treated
subgrade Carrollton soil is more than treated subgrade Dallas soil, which caused
the relatively significant improvement in pavement life.
Table 6.1 The properties of subgrade Dallas soil before and after treatment
Untreated Dallas Soil
Pavement Layers Moist Unit Weight
(g/cm3)
Thickness
(cm)
Resilient
Modulus
(MPa)
Asphalt Concrete
Pavement 2.32 5.08 3447.38
Flexible Base 2.08 15.24 344.74
Untreated Subgrade 1.82 20.32 35.85
Subgrade 1.82 - 35.85
Treated Dallas Soil (Third Ratio)
Pavement Layers
Moisture Unite
Weight
(g/cm3)
Thickness
(cm)
Resilient
Modulus
(MPa)
Asphalt Concrete
Pavement 2.32 5.08 3447.48
Flexible Base 2.08 15.24 344.74
Stabilized Subgrade 1.79 20.32 53.78
Subgrade 1.79 - 35.85
Table 6.2 The properties of subgrade Carrollton soil before and after treatment
Untreated Carrollton Soil
Pavement Layers
Moisture Unite
Weight
(g/cm3)
Thickness
(cm)
Resilient
Modulus
(MPa)
Asphalt Concrete
Pavement 2.32 5.08 3447.38
Flexible Base 2.08 15.24 344.74
Untreated Subgrade 1.91 20.32 31.72
128
Subgrade 1.91 - 31.72
Treated Carrollton Soil (Third Ratio)
Pavement Layers
Moisture Unite
Weight
(g/cm3)
Thickness
(cm)
Resilient
Modulus
(MPa)
Asphalt Concrete
Pavement 2.32 5.08 3447.38
Flexible Base 2.08 15.24 344.74
Stabilized Subgrade 1.84 20.32 31.72
Subgrade 1.91 - 31.72
Table 6.3 The pavement design life of flexible base on untreated and treated
Expansive soil
Soil Type Underneath
Flexible Base
Cracking Life
(million ESAL)
Rutting Life
(million ESAL)
Design Life
(year)
Untreated Dallas Soil 0.37 0.28 6.3
Treated Dallas Soil 0.40 0.74 7.5
Untreated Carrollton Soil 0.36 0.21 5.8
Treated Carrollton Soil 0.40 0.77 8.5
Figure 6.2 Bar chart of pavement life of flexible base located on expansive
subgrade soils before and after treatment
129
6.2 Slope Stability - Case Study
This section presents a hypothetical case study of stabilizing the slope of a
failed highway embankment by treating the top 8 ft of soil with LISS. A failed
embankment located near Randell Lake in Denison, Texas, along U.S 75 frontage
road, was selected to obtain the geometric configuration representing a typical
highway embankment (Figure 6.3 and Figure 6.4). Prior to failure, the Randell Lake
slope had a height of 35 ft., with a 3H: 1V slope ratio (Figure 6.4). The native soil
used to build the embankment had a high PI of 37, and had experienced severe
desiccation cracking, resulting in the degradation of the shear strength parameters
from peak to fully softened shear strength (FSS) (Jafari et al. 2019). The reduction
in the shear strength parameters, especially the effective cohesion, coupled with
rainfall events, were found to be primarily responsible for the slope failure.
Figure 6.3 The desiccation cracks in the upper side of the slope
130
Figure 6.4 The geometric configuration of the slope
The Dallas soil had similar PI and swell-shrink characteristics as the Randell
Lake slope, and was, therefore, used for this hypothetical case study. The geometric
configuration of the slope was kept the same as that shown in Figure 6.4, but the
material properties of the untreated and LISS-treated Dallas soils were used for the
slope stability analyses. To assess the improvement in the post-treatment
performance of the slope, a stability analysis was performed, assuming that the top
8 ft. of the slope required treatment (Figure 6.5). A commercial software package
that uses the equilibrium method of slope stability analysis was utilized to compute
the factor of safety (FOS) of the slope before and after treatment (double chemical
ratio and curing for 28 days). The Morgenstern-Price (M-P) method was utilized to
calculate the FOS values since it considers both force and moment equilibrium.
131
The basic parameters of Dallas soil before and after treatment, such as
moisture density, cohesion, and friction angle are shown in Table 6.4 and were
utilized to perform the slope stability analysis. Prior to treatment, the critical
surficial slip surface had an FOS of 1.53. Even though an FOS > 1.5 is considered
sufficient to ensure the stability of a slope, it should be noted that peak shear
strength parameters were used for analyzing the stability of the slope before
treatment. However, the failure of the actual slope was attributed to the reduction
in shear strength parameters, due to FSS and rainfall events (Jafari et al. 2019).
Since the slope stability analysis conducted as a part of this research study
represents a hypothetical case study, a comprehensive analysis with actual rainfall
data, permeability, and shear strength parameters of unsaturated surficial soils was
not possible. Rather, an increase in FOS after LISS treatment was used in
conjunction with the decrease in swell potential and fatigue of swelling (Figure 4.6)
to assess the applicability of LISS stabilization for improving the performance of
highway embankment slopes. According to the slope stability analysis result
presented in Figure 6.6, the factor of safety of treated Dallas soil was 1.7, and
increased by 13%, as compared with the FOS before treatment (FOS =1.5).
Therefore, it can be concluded that LISS can be effective in preventing the surficial
slope failures by imparting additional strength to the soil and reducing the swelling
potential. The decrease in the swell-shrink potential is expected to be effective in
132
preventing the reduction in shear strength of the soil from peak to fully softened
(Jafari et al. 2019).
Table 6.4 Basic properties of Dallas soil before and after treatment
Soil Types Moist Unit Weight
(pcf)
Friction Angle
(degree)
Cohesion
(psf)
Untreated Dallas Soil 113.5 23.5 48
Treated Dallas Soil 111.9 27.4 96.8
Figure 6.5 The geometry of slope in the software
(a) Untreated Dallas Soil
133
(b) Treated Dallas Soil
Figure 6.6 FOS of slope with untreated and treated Dallas soil
134
Chapter 7
SUMMARY OF FINDINGS AND FUTURE RECOMMENDATIONS
7.1 Introduction
Liquid ionic soils stabilizers have been used to treat expansive soils in Texas
over past twenty years. Due to the limited literature review and patent proprietary
issues, engineers are not willing to accept and use it in the field. The main purpose
of this research is to study the effect of LISS treatment on the improvements in
engineering properties of problematic expansive soils and comprehend the probable
stabilization mechanisms.
Two expansive natural soils sampled from Dallas and Carrollton in Texas
were treated with LISS, and the improvements in engineering properties were
studied as a part of this research study. After the basic soil properties were estimated,
a comprehensive testing program involving different physical, chemical, and
engineering tests were performed on the control soils, and LISS treated soils. Three
different dilution ratios were used to treat the soils and the changes in soil properties
including strength, stiffness and volumetric changes, before and after treatment
were studied. The optimum dilution ratio was selected based on the all-round
improvements in different engineering properties including strength, stiffness and
swell behavior.
Microstructural tests and some additional physical and chemical tests such
as pH, consistency limits, grain size distribution and moisture content estimation
135
were performed on the soils treated at the optimum dilution ratio. The treated
specimens were cured for different time periods to study the time-dependent
improvements in the engineering properties. The probable stabilization
mechanisms responsible for improvement in engineering properties of LISS treated
soils were assessed primarily based on the morphological changes observed in the
FESEM images, and the variation in the elemental and mineralogical compositions
detected from the EDS and XRD test results.
Furthermore, two hypothetical case studies pertaining to the rehabilitation
of a distressed pavement and remediation of a failed highway embankment slope
were used to evaluate the feasibility of using LISS treatment as an alternative
stabilizer for improving the performance of infrastructures built on expansive soils.
7.2 Summary of Findings
Based on the results from different tests listed above, the major findings
obtained from this research study are summarized below.
7.2.1 Findings from Physical, Chemical and Engineering Tests
1. Basic soil classification tests were performed on Dallas and Carrollton soils.
Both soils exhibited high PI values and swell potential, and were classified as CH.
Grain size distribution analysis on these soils indicated that Dallas soil has more
clay content than Carrollton soil.
2. The mineralogical composition and contents of the expansive soils such as
Montmorillonite, Illite and kaolinite were determined from the CEC, TP and SSA
136
values. According to the test results, Dallas soil exhibited the highest
Montmorillonite and Illite content while Carrollton soil exhibited the highest
kaolinite content.
3. From standard compaction results on LISS treated and untreated soils, the
MDD of all soils reduced (2%-7%) and the OMC value increased after treatment
(1%-20%). Dallas soil and Carrollton soil treated by double chemical ratio
exhibited highest OMC due to chemical reaction between LISS and expansive soils.
4. According to the UCS test results, although MDD of Dallas soil treated by
double chemical ratio was slightly less than that of untreated sample, the
compressive strength increased by 75% after curing the treated soils for 28 days.
Despite having the highest OMC and lowest MDD values, the Carrollton soils
treated with double chemical ratio experienced a 25% increase in the UCS value
after 28 days curing because of the high LISS content. The rise of UCS values in
both soils may be attributed to the soil flocculation after LISS treatment. An
increase in curing time caused higher compressive strength due to the continuous
chemical reaction between LISS and soil.
5. The resilient modulus values (MR) were found out to be influenced by OMC,
MDD and LISS content. In Dallas soils, although LISS content in the double
chemical ratio was more than the recommended ratio by the manufacturer, MR
value of the recommended ratio was slightly greater than those obtained
corresponding to the double chemical ratio because of relatively high OMC and
137
low MDD. The treated Carrollton soils exhibited an increase in MR up to 180% of
the control sample after 28 days of curing. Among three dilution ratios, soils treated
by double water ratio indicated the maximum MR due to lowest OMC. In addition,
these tested MR values in the laboratory were also compared with predicted MR
values through universal model. K1 and K2 values of treated samples were greater
than those of control specimen because of higher strength and stiffness after
treatment. However, K3 decreased after treatment due to increasing shear stress
resulting in lower resilient modulus.
6. In the 1-D swell test, it was found out that both soils treated by double
chemical ratio and cured for 28 days inhibited swell potential significantly due to
the high LISS content. The swell potential of 28 days cured Dallas soil, treated at
the double chemical ratio, was smaller than that of Carrollton soil. This can be
attributed to the high Montmorillonite and Illite content of the Dallas soil which
facilitated the chemical reaction process with LISS. Furthermore, the swell
potential gradually decreased and reached a stable state in the fatigue swelling test,
which proves that LISS has a positive impact on inhibiting the swell behavior of
soils in the long-term drying-wetting cycles.
7. From the linear shrinkage bar tests, slightly difference of shrinkage
potential was observed among control soil and soils treated with various dilution
ratios, for both the soil types. Hence, LISS may not be very effective in reducing
the shrinkage potential.
138
7.2.2 Findings in Microstructural, Additional Tests and Numerical Modeling
results
1. In the FESEM tests, unlike the control samples, a stark difference in
morphology change could be observed after treatment in both soils. The
individual clay particle in the control samples was not visible in the treated
specimen. Conversely, the new flaky reaction products fused clay particles
together. The bonding characteristics of this new reaction product may be
responsible for imparting higher stiffness and strength in the treated soils,
as compared with control samples.
2. In terms of EDS tests, the Al/Si ratios of clay particles and new reaction
products were analyzed before and after treatment. The Al/Si ratio of clay
particles for Dallas and Carrollton soils after treatment reduced as compared
with the control Al/Si ratios. However, the Al/Si ratio of binding products
formed at the surface were higher than those clay particles after treatment.
As LISS is an acid-based stabilizer, part of aluminate layer of clay particles
dissolved in the LISS and new reaction products formed on the surface due
to utilization of Al3+ dissolved in the solution.
3. After analyzing the XRD results before and after treatment, aluminum
orthophosphate (AlO4P) was observed to be formed in both treated soils.
This new product is known to exhibit binding and strength contributing
139
characteristics, which results in the enhancements in strength and stiffness
of LISS treated soils.
4. In the progress of variation in moisture content test, a reduction in water
content for both treated soils indicated the utilization of water for the
chemical reaction between LISS and soil. Based on the variation in moisture
content data, the extent of progressive chemical reaction in Dallas soil was
higher than that of Carrollton soil. The presence of higher Montmorillonite
and Illite content in Dallas soil resulted in a stronger reaction with the LISS
which probably utilized a higher portion of the mixing water, as compared
to the Carrollton soil.
5. The pH values of treated Dallas soil and Carrollton soil increased from 3 to
7.8 in 20 days due to H+ in the LISS was attracted to the negative charges
on the surface of clays, which indicated progressive chemical reaction
between soil and LISS. The rate of pH change in Dallas soil was higher than
that of Carrollton soil in the early stages of curing (5 hours after treatment)
due to higher Montmorillonite and Illite in Dallas soil as compared with
Carrollton soil. In addition, the increase in pH of treated specimens (close
to 7) indicates that LISS is an environmental-friendly stabilizer.
6. In the variation of grain size distribution from hydrometer test, the percent
of clay particles finer than 0.002 mm reduced from 65% to 32% in 28 days
of curing, which implied the increase in the grain size after treatment. The
140
grain size increased possibly due to the fusion of clay particles and
formation of aluminum phosphates/orthophosphates which has got binding
and strength contributing characteristics. Furthermore, the percent of clay
particles finer than 0.002 mm dropped to 35% within one day, which
indicates a strong chemical reaction between LISS and soil at the early stage.
7. The consistency limits of both soils before and after treatment were almost
the same. Although negative charges distributed on the surface of clay
particles attracted H+ in the LISS solution, the small size and low valency
of H+ failed to significantly flocculate and change the texture of clay
particles after treatment. Hence, there is no significant difference in the
consistency limits among untreated and treated soils
8. The pavement design and slope stability analysis were used to evaluate the
feasibility of implementing LISS as an alternative option for improving
expansive soils in these studies. The design life of pavement after treatment
increased on both soils as compared with that of control soils due to
improvement in resilient modulus after treatment. The global factor of
safety of expansive soils after treatment increased by 13% as compared to
that of the untreated slope (FOS=1.5). To certain extent, the LISS can be
effective in preventing the surficial slope failure by imparting the soil
strength and reducing the swell potential.
141
7.3 Future Recommendations
The effect of LISS on two expansive soils collected from Dallas, TX and
Carrollton, TXwere evaluated in current research. The results from series of test
results such as physical, chemical, microstructural, engineering, numerical tests,
variation in pH, moisture content, grain size distribution and Consistency Limits
have provided an in-depth understanding of probable stabilization mechanisms of
LISS. However, in order to comprehensively understand other expansive soil
treatment by LISS, future recommendations are listed below:
1. The consideration of treating other expansive soils outside Texas by LISS
will provide better understand of LISS treatment
2. The new product formed in this research is sensitive to the temperature. It
is highly encouraged to find out the variation in the new products with
changing the temperature.
3. Except three dilution ratios mentioned in this study, other dilution ratios
should be studied to provide better understanding of LISS treatment.
142
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