Innovative ground improvement techniques for expansive … · Stabilization of expansive soils...

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

[email protected]

1 University of Texas at Arlington, Arlington, TX, USA

123

Innov. Infrastruct. Solut. (2017) 2:24

DOI 10.1007/s41062-017-0079-2

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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]

24 of 15 Innov. Infrastruct. Solut. (2017) 2:24

123

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]

Innov. Infrastruct. Solut. (2017) 2:24 of 15 24

123

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


123

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


123

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


123

(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]


123

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]


123

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


123

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


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]


123

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]


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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