Innovative ground improvement techniques for expansive … · Stabilization of expansive soils...
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TECHNICAL PAPER
Innovative ground improvement techniques for expansive soils
Anand J. Puppala1 • Aravind Pedarla1
Received: 3 May 2017 / Accepted: 2 June 2017 / Published online: 19 June 2017
� Springer International Publishing AG 2017
Abstract Annual infrastructure damage expenses arising
from expansive problematic soils cost millions of dollars.
These damages signify the need to study the treatment
methods in a much more comprehensive manner with a
focus on resiliency and sustainability elements. Many
advances are made in recent years with respect to chemical
additive-based stabilization methods. This keynote paper
covers innovative ground improvement advances majorly
focusing on civil and transportation infrastructure. Four
research studies highlighting the importance of additive
soil stabilization are presented. Chemical stabilization
advances ranging from shallow stabilization design
guidelines with incorporation of fundamental soil chem-
istry principles, clay mineralogy, novel chemical additives,
durability studies and resiliency elements are covered.
Enhancement of soil strength due to the addition of lime
and cement and the mixture’s resiliency to climatic chan-
ges are studied. Sustainable biopolymer treatments to arrest
desiccation cracking on slopes have been addressed. In the
case of deep soil treatment, deep soil mixing technologies
are described for stabilization of soils to support pavement
infrastructure. Future research directions related to sus-
tainable ground improvement practices are presented.
Keywords Expansive soils � Ground improvement � Clay
mineralogy � Stabilization effectiveness � Shallow and deep
soil stabilization
Introduction and background
Natural expansive soils have been found in many places
around the world. These soils undergo large volumetric
changes due to moisture fluctuations from seasonal varia-
tions and cause swell and shrinkage movements in soils,
which in turn will inflict severe damage to structures built
above them [22]. Examples of expansive clays include high
plasticity or high PI clays, over consolidated clays rich
with montmorillonite clay minerals, and shales. It was
reported that the expansive soils damage to structures,
particularly light buildings and pavements that are much
greater than the damages caused by other natural disasters
like earthquakes and floods [13].
The problem with expansive soils was first recognized
by engineers as early as late 1930s [4]. Since then, the
increase in population and subsequent urbanization pres-
sure encouraged the use of problematic sub-soils, including
soft and expansive soils, for construction purposes. This
initiated researches and practitioners to find structural
alternatives to minimize the distress caused to superstruc-
ture due to differential expansive soil movements [31, 33]
Several countries in the world, including the United
States, Turkey, Egypt, India, China, South Africa, and
Australia, have reported infrastructure damage caused by
the movements of expansive soils. The damages and repair
costs are estimated to be several billions of dollars annually
[2, 12, 21]. Below presented are some of the commonly
observed infrastructure distresses caused due to swell/
shrink behavior of expansive soils.
Damages to roads from expansive clays
Numerous roads constructed on expansive clay subgrades,
especially in the east and central Texas, USA, though over-
This paper was selected from GeoMEast 2017—Sustainable Civil
Infrastructures: Innovative Infrastructure Geotechnology.
& Anand J. Puppala
1 University of Texas at Arlington, Arlington, TX, USA
123
Innov. Infrastruct. Solut. (2017) 2:24
DOI 10.1007/s41062-017-0079-2
designed, still encounter severe pavement cracking with
short serviceability life. The maintenance costs, in some
cases, are even more than their construction costs [33].
Pavements or roads that are constructed on soft and prob-
lematic soils have frequent maintenance problems. The
subgrade soils, in particular expansive soils, should be
better accounted for both during design and construction of
the roads [29]. Figure 1 presents some of the deformations
and cracks occurred in pavements constructed on expan-
sive soils in Texas, USA.
Shallow Slope failures caused due to expansive soils
Surficial failures are often witnessed at a number of earth
fill dam sites, levees, highway embankments, and cut
slopes. Surficial slope failures on earthen dams constructed
on expansive soils are commonly observed due to the soils
unstable nature to seasonal events. These surficial failures
are classified as shallow slope failures as the average depth
of failure varies from 1 to 4 ft. [11], with only a surficial
portion of soil sliding downward. Rahardjo et al. [35]
showed that surficial failure occurs after wetting–drying
cycles, when water infiltrates the soil through desiccation
cracks and reduces the shear strength of the soil mass.
Figure 2 below presents a surficial failure occurred at
Bardwell Dam, Texas, USA.
Joe Pool Dam and Grapevine Dam which are located in
the Dallas Fort Worth Metroplex in the state of Texas, USA
are victims of surficial failures due to the presence of
expansive soils. Both the dams selected have experienced a
large number of surficial failures since their inception [20].
At Joe Pool Dam, the first failure occurred within 2 years
of its construction, followed by number of surficial failures.
At Grapevine Dam, more than 20 surficial failures were
observed within 40 years of its construction [20]. Most of
the embankment failures were attributed to prolonged
rainfall events immediately after summer droughts that
result in desiccation cracking of the surficial parts of the
embankments. Figure 3a, b shows the failures occurred at
two dam sites due to surficial slope failures.
Analysis of these failures reveals that the highest num-
ber of failures occurred during the hotter summer months
between March and August. The failures have sometimes
repeated either at the same location or close proximities,
due to the expansive nature of the in situ soils.
Stabilization of expansive soils
Enhancement of soil strength and stiffness properties and
mitigation of volume change behavior with additive
inclusion has been implemented as early as 1930s [4]. The
increase in population and subsequent urbanization has
often resulted in the construction of highways on soft and
problematic sub-soils. Soil treatment alternatives such as
chemical additive-based stabilization, pre-wetting, soil
replacement and compaction control, moisture control,
surcharge loading and thermal methods are often used to
stabilize expansive soils [22].
Additive stabilization technique is widely used in the
construction of roads, airports, embankments, or canal
Fig. 1 Cracking in pavements
caused by expansive soils in
Texas, USA [29]
Fig. 2 Surficial slope failure at Bardwell Dam, Texas, USA [20]
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linings by mixing with clayey soils to improve their
workability, strength, stiffness, swelling characteristics and
bearing capacity of native soils [30, 31].
Modifications in physio-chemical properties of expan-
sive soils prove to be more effective on a long-term basis
[29–33]. Physical changes due to macro structural changes
in treated soils could help in the reduction of expansive soil
behavior by reducing void ratios of natural expansive soils.
The permanency of chemical treatments often controls
overall effectiveness of soil stabilization.
Traditional chemical stabilizers typically depend on
pozzolanic and cationic exchange reactions to modify and
stabilize soils (NCHRP 114 2009). Pozzolanic reactions
occur when siliceous and aluminous materials in soils react
chemically with calcium hydroxide and other chemicals
from stabilizers to form cementitious compounds or gels.
Cation exchange also occurs when the soil is able to
exchange free cations available in exchange locations,
thereby resulting in changes of moisture affinity charac-
teristics (Mitchell and Soga [21]; [7]. Lime, cement, and fly
ash are the most frequently used chemical additives in soil
stabilization practices.
Lime and cement are the most widely used stabilizers in
engineering practice since early times and have applica-
tions over wide range of soils [17, 26]. Lime/cement
additive stabilization technique is considered to be very
effective for reducing swell/shrink potential, plasticity,
strength and increasing workability of expansive soils
[4, 22, 33]. The most substantial improvements in these
properties are seen in moderately to highly plastic clays
[10, 16, 32], Puppala et al. [28].
When a clayey soil is treated with lime and reacts in the
presence of water, compounds are formed through the
processes of cation exchange, flocculation, carbonation and
pozzolanic reaction [1]. Tobermorite gel formation in
cement-treated soils is a well-known factor for soil strength
enhancement. Stabilizers react with soils at physio-chem-
ical and micro-structural level altering the properties as
mentioned above [37].
In projects where soil compressibility properties need to
be enhanced to reduce undesirable settlements, either lime
or combinations of lime with cement or other additives are
typically used in deep soil mixing treatments [33, 34].
This paper presents select studies including four
research studies on these soil treatments with an aim to
further advance these stabilization methods by incorporat-
ing durability studies as well as soil mineralogy details into
the mix design. The following research studies conducted
at UTA provide the importance of both clay mineralogy of
expansive soils, wetting and drying studies to address the
efficacy of chemical treatments and deep soil mixing
treatment studies and all these aim to improve the prob-
lematic nature of expansive soils.
Description of stabilization studies
Research study 1: durability issues
In any stabilization application, the stabilized material is
desired to withstand climatic variations, such as being
subjected to severe wetting and drying cycles from sea-
sonal changes. The action of wetting and drying plays an
important role in assessing the durability of treated soils.
Durability relates to the permanency of chemical stabilizers
and the ability for soil particles and stabilizers to hold
together and remain intact for a long period of time. Long-
term performance of the specimens can be replicated in the
laboratory by freeze–thaw and durability studies. The
effect of freeze–thaw on strength can be explained in terms
of the retardation or acceleration of the cementitious
reactions. At UTA, two experimental studies including
Fig. 3 Showing surficial slope failures at a Grapevine Dam b Joe Pool Lake Dam, Texas, USA [20]
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Chittoori et al. [7, 8] and Pedarla et al. [25] investigated
highly expansive soils from various regions in Texas, USA.
Soil specimens were prepared using the static compaction
method. All soils were subjected to clay mineralogy studies
and the techniques used to attain these results can be found
in Chittoori and Puppala [6]. Soils were later subjected to
durability studies and the summary of these test results is
presented in the following sections.
Wet-dry durability studies
Durability studies are typically conducted on soil samples,
either with or without stabilizers, to duplicate field climatic
conditions in the laboratory within a shorter time period.
ASTM D559 provides a testing guideline to replicate
moisture and temperature fluctuations occurring in the
field. Soil specimens were then cured for 7 days in a
moisture room prior to subjecting them to wet-dry cycles.
Each wet-dry cycle corresponds to submerging the soil
samples in water for 5 h and then placing them in a 70 �Coven for 42 h. Specimens were subjected to volume change
and moisture content measurements during the cycles.
The accelerated curing process requires that the soil
specimen be subjected to drying by placing it in a pre-
heated oven at 40 �C for 48 h. After drying, the soil
specimen was left to cool for a period of 1 h and then
subjected to back saturation for 24 h. Cured specimens
were brought to optimum moisture content (OMC) prior to
testing them for W/D cycles. Durability studies were
conducted on all soils by alternating wetting and drying
cycles as shown in Fig. 4. In accordance with ASTM D559
method, each wet-dry cycle consists of submerging the soil
specimens in water for 5 h and then placing them in an
oven at 70 �C for 48 h. Both volumetric changes and
strength loss were monitored and presented for all soil
samples at various cycles.
One of the important highlights of the UTA experi-
mental investigations is that all soils that were studied for
durability studies were first characterized to determine their
mineralogical composition. Details of these mineralogical
analyses can be found in Chittoori et al. [7, 8] and Chittoori
and Puppala [6]. Durability studies at UTA on lime- and
cement-treated expansive clays showed that the presence of
Montmorillonite diminishes stabilization effectiveness. For
example, two soils exhibited distinct behavior to stabi-
lization using recommended dosages. Keller soil belongs to
the family of low-plasticity clays (CL) and the clay fraction
of the soil contained 60% kaolinite and 20% Montmoril-
lonite and Illite. From the standard design procedures (Tex-
121-E), 6% lime was added for stabilization. Keller soil is
regarded as Kaolinite-rich soil.
Figure 5a, b shows the UCS test results and volumetric
strains of the control and treated soil specimens. Untreated
Keller soil showed an initial UCS of 31 psi (217 kPa) and
survived for one cycle of W/D, experiencing a maximum
volumetric strain of 27%. Treated soil specimen showed an
initial strength of 53 psi (370 kPa) and survived for 21
cycles of W/D, retaining 85% of its initial strength. The
Keller soil specimen was effectively stabilized as it met the
survivability criteria (i.e., 21 W/D cycles with a volumetric
strain of less than 10% and high retained UCS values).
Austin soil had 40% Montmorillonite content and
belongs to the class of high plasticity clays (CH). Austin
soil is regarded as Montmorillonite-rich soil in this paper.
The optimum amount of stabilizer required to effectively
stabilize the soil specimen was 6% lime according to the
standard stabilization charts. However, when subjected to
durability testing, the maximum volumetric strain
Fig. 4 a Wetting and b Drying cycle setup
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exhibited by the 6% lime-treated soil specimen is close to
15%, whereas the control soil specimen exhibited 55%.
The UCS of the treated soil specimens was higher than the
control, but the treated specimens did not survive all 21 W/
D cycles as presented in Fig. 6a and b.
To determine the effective stabilizer dosage, this soil
was further stabilized with 8% lime, 3% cement, and 6%
cement. The optimum amount of stabilizer for Austin soil
for effective performance was 6% cement. 6% cement-
treated soil specimen exhibited only 5% volumetric strain
for 21 W/D cycles. The maximum UCS exhibited by the
treated soil specimen was 225 psi (1575 kPa) as shown in
Fig. 6a. This value is very high when compared with the
UCS of the control soil specimen, which was 34 psi
(238 kPa). Images of the Austin test specimen collected
after different durability cycles are presented in Fig. 7.
The volumetric strain for the soils was effectively
reduced when the stabilizer dosage increased [25]. Table 1
summarizes the retained strength measurements along with
the maximum volumetric strain change at the end of the
Fig. 5 a Volumetric changes and b unconfined compressive strength variation with W/D Cycles for treated and untreated Kaolin-rich Keller soil
specimens
Fig. 6 a Volumetric changes and b unconfined compressive strength variation with W/D cycles for treated and untreated Montomorillonite-rich
Austin Soil Specimens
Innov. Infrastruct. Solut. (2017) 2:24 Page 5 of 15 24
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W/D tests with a W/D cycle survival count listed for all the
eight soils tested. Further discussion on these results and
observations is presented in the following section.
This indicates that soils containing Montmorillonite as a
dominant mineral are more susceptible to premature
strength failures after chemical stabilization when they are
exposed to volume changes caused by moisture move-
ments. Figure 8 presents a modified chemical stabilizer
design method by accounting for clay mineralogy, mostly
by including the percent of Montmorillonite (M). It can be
observed from Fig. 8 that, as the Montmorillonite per-
centage increased in the clay fraction, the retained strength
after 7 W/D cycles decreased while the volumetric strain
change increased. This is an important finding as it shows
the influence of clay mineralogy on the durability of
chemical stabilizers in providing sustained strength over a
long time period. In this research, three dominant clay
mineral types are studied and their influence on stabiliza-
tion effectiveness is addressed. Mix design procedures
outlined in this paper are valid to these soils as well and
author recommends performing comprehensive laboratory
mix designs to limited field verification studies when soils
encountered in the field contain characteristics that are
different from those discussed in the paper.
Additional soil types with different mineralogical and PI
properties should be studied to expand and further validate
the proposed design chart. From this study, it is found that
the influence of mineralogy on the long-term performance
of stabilized expansive soils is evident, and soils having
high mineral content show less resistance to failure when
stabilized.
It was observed in this study that samples that retained
at least 80% of their initial strength after seven W/D cycles
lasted for all 21 W/D cycles retaining at least 50% of their
initial strength. Based on this observation, it can be
deduced from Fig. 8 that soils containing more than 40%
montmorillonite minerals in their clay fraction may not be
efficiently stabilized with lime, as 8% lime content is
considered the upper limit for stabilization purposes and
anything beyond 8% may not be economical.
Research study 2: surficial slope treatments
Two dam sites, Joe Pool Lake dam and Grapevine Dam
located in Fort Worth, Texas area were selected for the
research, where surficial slope failures have occurred in the
past. To mitigate these failures, a research study was
undertaken by The University of Texas at Arlington
Fig. 7 Images of treated Austin samples subjected to different wetting/drying cycles
Table 1 Volumetric strain and retained strength at the end of wetting/drying cycles for all eight W/D cycle surviving soils treated with lime
using standard procedures
Soil name Dominating clay mineral Amount of additive,
(% by weight)
# of cycles sample survived Volumetric strain (%) Retained strength (%)
Austin Montmorillonite 6% 7 15 0
Fort Worth Montmorillonite 6% 10 15 0
Paris Montmorillonite 8% 7 15 0
Pharr-A Montmorillonite 4% 4 30 0
Bryan Kaolinite 8% 21 6 93
Keller Kaolinite 6% 21 5 80
Pharr-B Kaolinite 3% 8 18 0
El Paso Illite 8% 21 12 80
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(UTA). The main objective of this study is to explore the
best field stabilization method to mitigate desiccation
cracks in the upper embankment soils of the two dams.
The soils collected from the dam slopes were first sub-
jected to basic laboratory tests for their classification.
Table 2 presents a summary of the basic soil characteri-
zation studies of test soils.
For this study, the four admixtures that were selected to
treat surficial soils were: 20% compost, 4% lime with
0.30% polypropylene fibers, 8% lime with 0.15%
polypropylene fibers, and 8% lime. Five test sections,
including four treated sections and one control section
without any surface treatment, were constructed at each
dam site as shown in Fig. 4a and b. During the construction
of the dam, the core soil was overlain by a topsoil of about
23 cm (9 in.) thick for the purpose of vegetation growth.
The treatment of admixtures was intended to be mixed with
the core soil of the dam. First, the top soil was excavated
using a back hoe, then stockpiled aside for reuse to place it
back over the treated section after compaction of the 45 cm
(18 in.) thick soil layer mixed with admixtures on the slope
surface. The core dam soil was excavated and placed in the
level pad area. It was then pulverized, moistened and
mixed with admixtures before being transported and placed
back in the embankment as shown in Fig. 9b.
The test sections were instrumented with inclinometers
as shown in Fig. 9c. The test sections as shown in Fig. 9d
have been monitored for a period of 3.5 years at Joe Pool
Dam and 2.5 years at Grapevine Dam. With the different
types of soil at each dam site, the results gave a better
insight into the aspects of the behavior of clayey soils when
treated with chemical admixtures.
From Fig. 10a and b, it can be understood that the
control soil section continued to show lack of resistance
against shrinking and swelling phenomenon, resulting in
the maximum movement compared to other treated sec-
tions at both Joe Pool Dam and Grapevine Dam. 20%
compost-treated sections started displaying their
Fig. 8 Modified stabilization
process, results, and post-test
recommendations by UTA
Group
Table 2 Summary of
laboratory test results of GV and
JP soils
Soil properties Joe Pool Lake soil Grapevine soil
% passing No.200 Sieve 70 58
% clay fraction 20 18
Specific gravity, Gs 2.71 2.73
Liquid limit, LL 58 30
Plasticity index, PI 34 13
Maximum dry density, MDD (kg/m3) 1494 1733
USCS classification CH CL
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inconsistencies in long-term performance. 4%
lime ? 0.30% fibers and other lime-treated sections per-
formed well at both sites.
It may also be inferred from the above graphs that the
shrinkage tendency of the soil from both sites exceeded
swelling-related movements, specifically at Joe Pool Dam
site. The control section continued to exhibit the highest
movement in comparison with other treated sections.
Chemical stabilization of expansive soils using calcium-
based stabilizers like lime improved soil strength, stiffness,
durability and a reduction in soil plasticity and swell/
shrinkage potential. The above research study revealed that
lime with and without fiber treatment of shallow soils is
regarded as a promising way for slope stabilization, which
can mitigate desiccation cracking of expansive soils on
embankments and, thereby, enhances surficial slope
stability.
Research study 3: biopolymer soil treatments
Biopolymer is an organic polymer that is produced natu-
rally from living things [36]. These are mostly high
molecular weight polysaccharides that contain chemically
active groups with electrical charges and interact with clay
minerals [36]. The natural benefits of biopolymer are sur-
face adhesion, self-adhesion of cells into biofilm, formation
of protective barriers, water retention around roots of
vegetation, and nutrient accumulation [14]. These attri-
butes enhance the shear strength of soil to reduce erosion
and surficial failure of slopes [24].
Guar-Gum biopolymer is naturally occurring biopoly-
mer and is a neutrally charged plant polysaccharide.
Researchers found Guar-Gum to be more effective than
xanthan gum due to the higher viscosity of the guar gum
solution [5, 23]. Improvements to soil structure by electric
double layer thickness reduction and cation bridging
between polymer and clay were observed in Guar-Gum
treated soils [23].
In this study, same Grapevine and Joe Pool soils were
mixed with Guar-Gum and compacted at the 95% of
maximum dry density and optimum moisture content.
Specimens for direct shear tests were prepared by static
compression of the soil–biopolymer–water mixture. After
mixing, 25 mm thick and 63.5 mm diameter specimens
were carefully molded and then placed in an airtight plastic
wrap and transferred to a humidity chamber. Treated
Fig. 9 Showing a Excavation, b lime treatment, c Inclinometer casings and d Shallow-treated soil sections [15]
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specimens were allowed 7 days of curing time before the
test. The curing method was aimed at achieving moisture
homogenization within the specimen, yet maintaining the
optimum moisture content. Direct shear tests were per-
formed at the designated normal stresses of 50, 100, and
200 kPa. The tests were performed using a very slow shear
rate of 0.005 mm/min (0.0002 in/min). Figure 11 presents
the direct shear test results for Grapevine (GV) and Joe
Pool (JP) soils.
Figures 12 and 13 present the variation in the effec-
tive cohesions and friction angles with Guar-Gum dosa-
ges for both soils. The effective cohesion of the
Grapevine soils increased abruptly up to a Guar-Gum
dosage of 0.5% and then started decreasing gradually.
The effective cohesion for 1 and 1.5% Guar-Gum con-
tents was lower than that for 0.5% Guar-Gum. On the
other hand, the friction angle remained almost at
constant level over the range of the Guar-Gum contents.
However, the friction angles for 0.25 and 0.5% dosages
were slightly higher than those for the rest of the
dosages. Similarly, effective cohesion of the Joe Pool
soil showed a major increase up to 0.5% dosage and
then it increased gradually at higher concentrations. 1.5%
dosage had the maximum effective cohesion. On the
other hand, the friction angles of the Guar-Gum treated
soils showed a gradual downward trend with increase in
the Guar-Gum dosage.
The above observations indicate that the optimum Guar-
Gum stabilizer dosage is around 0.5% for these soils.
Therefore, the optimum dosage of 0.5% Guar-Gum was
considered for additional tests and slope stability analyses.
The general trend of decrease in shear strength at higher
contents of Guar-Gum can be attributed to the lubrication
of the soil particles by the biopolymer.
Fig. 10 Showing comparison
of movement measured at
different test sections by
inclinometer at a Grapevine
Dam, b Joe Pool Dam [15]
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0 50 100 150 200 250
Effective normal stress (kPa)
0
20
40
60
80
100
120
140
160
180
Shea
r st
ress
(kPa
)
0
400
800
1200
1600
2000
2400
2800
3200
3600
Shea
r st
ress
(psf
)
Soil typeControl soilControl soil0.25%BP treated0.25%BP treated0.5% BP treated0.5%BP treated1%BP treated1%BP treated1.5%BP treated1.5%BP treated
0 1000 2000 3000 4000 5000Effective normal stress (psf)
Grapevine soil
(a)
0 50 100 150 200 250Effective normal stress (kPa)
0
20
40
60
80
100
120
140
160
180
Shea
r st
ress
(kPa
)
0
400
800
1200
1600
2000
2400
2800
3200
3600
Shea
r st
ress
(psf
)
Soil typeControl soilControl soil0.25%BP treated0.25%BP treated0.5% BP treated0.5%BP treated1%BP treated1%BP treated1.5%BP treated1.5%BP treated
0 1000 2000 3000 4000 5000Effective normal stress (psf)
(b)
Fig. 11 a Failure envelopes of
Grapevine soil, b Joe Pool soil
0 0.4 0.8 1.2 1.6
Biopolymer content (%)
0
5
10
15
20
25
Effe
ctiv
e co
hesi
on (k
Pa)
0
5
10
15
20
25
Effe
ctiv
e co
hesi
on (k
Pa)
Soil typeJP BP treatedGV BP treated
0 0.4 0.8 1.2 1.6Biopolymer content (%)
Fig. 12 Variation in the effective cohesions of the Grapevine and Joe
Pool soils at different dosages of biopolymers
0 0.4 0.8 1.2 1.6
Biopolymer content (%)
20
25
30
35
Effe
ctiv
e fr
ictio
n an
gle
(deg
rees
)
20
25
30
35
Effe
ctiv
e fr
ictio
n an
gle
(deg
rees
)Soil typeJP BP treated GV BP treated
0 0.4 0.8 1.2 1.6Biopolymer content (%)
Fig. 13 Variation in the effective friction angles of the Grapevine
and Joe Pool soils at different dosages of biopolymers
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Current research studies are exploring the use of
biopolymer treatments in real field test sections. Based on
the field performance studies, these methods can be good
alternates for stabilizing surficial soils as any increase in
effective cohesion intercepts would enhance their stabili-
ties in the case shallow slope failures.
Shallow soil stabilization is most often used method in
practice. Depths of the soil treatment vary from 0.3 to
1.5 m. However, when these soils extend beyond 2–3 m,
they need to be stabilized with soil mixing and grouting
techniques. Deep soil mixing (DSM) method is one such
ground modification technique that improves the quality of
ground by in situ stabilization of soft soil or by in situ
fixation of contaminated ground [27]. Deep mixing (DSM)
technology involves the auger mixing of soils extending to
large depths with cement, lime, or other types of stabilizers
and co-stabilizers. The final and last research study pre-
sented in the following briefly describes one such appli-
cation for stabilizing expansive soils of 3–4 m in depths.
Research study 4: deep soil mixing studies
Researchers at UT Arlington have studied in evaluating the
application of deep soil mixing (DSM) technique for sta-
bilizing expansive sub-soils of considerable depths beneath
the pavements. In the process, researchers proposed con-
struction and monitoring of two DSM-treated pilot scale
test sections along the median of Interstate 820 in Haltom
City, Texas [19]. The interstate is underlain by expansive
sub-soils and is under consideration for reconstruction and
expanding the current two lane highways to four lanes.
Laboratory mix design and details are presented in Mad-
hyannapu et al. [19].
A pilot test section was considered for deep soil mixing
and the details of test site are shown in Figs. 14, 15 and 16.
The dimension of test sections along the median is 40ft in
length and 15 ft in width.
The construction of DSM-treated prototype test sections
took place in May 2005 and installation of DSM columns
in each section was completed in 1� to 2 days. The col-
umn dimensions are 2 ft in diameter and 10 ft in length.
The construction of DSM-treated test sections is followed
by instrumentation to evaluate the performance of these
sections based on the data obtained from monitoring for a
period of 2 years (Aug 2005–Aug 2007). The construction
procedure of DSM column installation and the prepared
columns is shown in Fig. 15 below.
In this study, horizontal inclinometer (HI) casings of
3.34 in. dia. were installed at the surface of treated and
untreated sections. The inclinometers were surveyed reg-
ularly for every 2 weeks to observe the behavior of
treated sections with environmental changes. Results from
vertical inclinometers showing lateral movement of sub-
soils of untreated and treated sections are presented in
Fig. 17.
From Fig. 17, vertical soil movements monitored from
horizontal inclinometers installed in treated area showed
considerably lesser soil movements than those monitored
in untreated soil sections utilizing elevation surveys. The
reduction in surface movement in DSM-treated sections
was attributed to the improvement achieved through DSM
technique, thus indicating effectiveness of deep soil mixing
methods used in the present research [19]. Lateral soil
movements recorded using vertical inclinometers installed
in both treated and untreated sections were low.
Sustainability metrics in ground improvement
Sustainability topics for discussion and research in
geotechnical engineering have been mostly concentrated
on the ground improvement topics by introducing novel
and environment-friendly ‘greener’ materials, reusing
waste materials with some form of stabilization, enhancing
the durability performance of the materials, and use of
composite materials. It is essential to study and evaluate
the performance of the ground treatment options and their
sustainable benefits to the infrastructure.
Basu et al. [2] and very recently Correia et al. [9] pro-
vided a comprehensive literature on sustainability in
geotechnical engineering and its implication in trans-
portation infrastructure. Correia et al. [9] covered various
topics ranging from sustainable ground improvement
methods, earthworks constructed by minimizing the use of
energy and the production of CO2, and the use of recycled
alternative materials, foundation reuse, and rehabilitation
and maintenance without the consumption of large
amounts of primary natural geomaterials.
With respect to ground treatment options, Correia et al.
[9] noted that the choice of ground improvement option for
a particular infrastructure project which is usually made in
deference to the project cost and timelines is now consid-
ering sustainability standpoint as well. Engineers and
practitioners can design and choose two or three ground
improvement alternatives for a given project and then
perform comprehensive analyses of the carbon footprint,
life cycle cost and energy consumption of each of the
methods and then determine the one that proves to be the
most sustainable solution to the given project. In doing
such analyses, project cost details are implicitly covered.
There are many elements known as sustainable indica-
tors that one must consider in the evaluation phase of
ground treatment options and some of these are identified
as: use of materials resources, use of energy resources,
emissions to air, soil pollution, water use and reuse, noise
and vibrations, productions of waste and management,
species and ecosystem, population, societal involvement
Innov. Infrastruct. Solut. (2017) 2:24 Page 11 of 15 24
123
and many others. All these indicators have to be considered
and assessed. Typically, all these will provide information
to a more comprehensive sustainable analysis which must
include a comprehensive life cycle cost studies to address
the incorporation of new design features in ground
improvement, and a carbon foot print analysis that con-
siders stabilizer types and their use in the project. Many
sustainability rating organizations provide ratings based on
the material reuse along with consideration of recycled
materials of chemical nature for stabilizations.
Sustainable benefits of reusing in-place old pavement
materials with chemical stabilization offer many sustain-
able benefits including less amount of landfill, have to be
landfilled, lower overall carbon footprint of the project, less
pollution caused by quarrying, and reduced traffic delays
and others. Cost and environmental benefits, as well as
Fig. 14 Schematic of DSM columns at the pilot test site [19]
Fig. 15 a Auguring of DSM columns, b Manufactured DSM columns [19]
Fig. 16 Inclinometer instrumentation in the field [18]
24 Page 12 of 15 Innov. Infrastruct. Solut. (2017) 2:24
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environmental emission reductions of using in situ stabi-
lized old pavement material versus imported quarry
aggregate materials, clearly show the true benefits of using
chemical treatments in the field works.
Another aspect of sustainability design is the selection
and dosages of chemical additives and how much of a
carbon foot impact that they will have in the design of
composite stabilization method for a transportation
infrastructure construction project. For example, the
dosage amounts of carbon numbers and analyses with
respect to utilization of lime or cement or use of com-
binations of lime or cement and recycled co-additives
will determine the impacts of soil stabilization design
and selections in the present ground improvement
considerations.
More details on these analyses, along with life cycles
cost benefit studies, are implemented in the traditional
stabilization design and selection processes. This is
expected to preserve our natural resources and environ-
ment by reducing emissions and reducing carbon foot-
print analyses. Future studies focus on other
considerations including other energy considerations
from construction, air pollution and waste generation.
More such frameworks would enhance the utilization of
byproducts in the soil stabilization as a part of greener
infrastructure design.
Summary and findings
In the present paper, four research studies involving addi-
tive stabilization to mitigate expansive soil behavior at both
shallow and deep depths have been presented. First three
studies focused on shallow soil treatments and the final and
fourth study focused on deep soil mixing treatment
application.
In the first study, the role of clay minerals in the durable
performance of stabilized soils is explained and a novel
mix design method by accounting for clay mineral percent
in the design is developed. Second study involves mitiga-
tion of surficial slope failures caused from swell/shrink
behavior of expansive soils. The soils at the site were
treated with four stabilizers and elevation surveys over a
period of time showed the improvements of the treated
soils over the control or untreated soils. Among the treat-
ments, 8% lime ? 0.15% fibers and 8% lime-treated soils
were ranked the top two treatments as their sections
exhibited 50–60% less vertical movement than the control
untreated section.
In the third shallow stabilization study, biopolymers
have been addressed to improve the stability of slopes
constructed with problematic soils. Biopolymer-treated
soils showed a moderate improvement in the shear strength
but effectively mitigated the shrinkage characteristics of
the native material. This would prevent any further
Fig. 17 Inclinometer data from
untreated and treated sections
[18]
Innov. Infrastruct. Solut. (2017) 2:24 Page 13 of 15 24
123
moisture infiltration into the slope, thereby preventing
shallow slope failures.
The final research study focused on deep soil treatments
and the performance of DSM columns in expansive soils was
studied and evaluated. Both lime and cement additives were
used as stabilizers in this study. Test sections were built on
DSM columns and instrumented with inclinometers and
pressure cells. From the inclinometer data, it was observed
that the treated soil section did not undergo any movement
compared to the untreated sections. Considering that the
overall performance of DSM-treated sections compared to
untreated sections at sites, it can be concluded that DSM-
treated section has provided successful treatment in mitigating
the swell-shrink movements related to moisture changes.
A brief overview of sustainability framework incorpo-
rating additive stabilization has been discussed and this has
been a major focus of ongoing studies as sustainable
metrics of the treatments will enhance their green value
potential in the mega construction projects.
Acknowledgements The authors would like to thank Texas Depart-
ment of Transportation and US Army Corps of Engineers—FW
District for supporting these studies and in providing necessary help
for field implementation of these stabilization methods. Several for-
mer doctoral students, Bhaskar Chittoori, Raja Sekhar Madhyannapu,
Minh Le, Venkat Dronamraju assisted in the experimental works as a
part of their doctoral studies. Their assistance is acknowledged.
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