Testing and Modeling the Short-Term Behavior of ...

Geotech Geol Eng DOI 10.1007/s10706-015-9890-8

ORIGINAL PAPER

Testing and Modeling the Short-Term Behavior of Lime and Fly Ash Treated Sulfate Contaminated CL Soil Ahmed Mohammed . Cumaraswamy Vipulanandan

Received: 15 December 2013 / Accepted: 22 April 2015 Ó Springer International Publishing Switzerland 2015

Abstract In this study, the effects of calcium sulfate contaminated soil treatment methods on the index properties, compacted soil properties, free swelling and compressive stress strain relationship of a CL soil obtained from the field was investigated. Calcium sulfate concentration in the soil was varied up to 4 % (40,000 ppm) and the soil samples were cured for seven days at 25 °C and 100 % humidity before testing. With 4 % sulfate contamination the liquid limit and plasticity index of the soil increased by 44 and 81 % respectively. The free swelling increased from 7 to 18 % and the compressive strength decreased by 65 % with 4 % of calcium sulfate, Also the study investigated the effects of fly ash (class C) and hydrated lime treatment on the behavior of treated sulfate soils. X-ray diffraction (XRD) was used to characterize the soil and the reaction products of lime and fly ash treated soils. Based on XRD analyses, major constituents of the CL soil were calcium silicate (CaSiO3), aluminum silicate (Al2SiO5), magnesium silicate (MgSiO3) and quartz (SiO2). Addition of calcium sulfate resulted in the formation of calcium

silicate sulfate [Ternesite Ca5(SiO4)2SO4] and aluminum silicate sulfate [Al5(SiO4)2SO4]. Treatment with lime resulted in the formation of ettringite [Ca6Al2(SO4)3(OH)1226H2O]. Treating with fly ash resulted in the formation of calcium silicate hydrate (CaSiO3H2O) and magnesium silicate hydrate (Mg3SiO3H2O), cementing by products. Contaminated soil treatment with lime and fly ash reduced the index properties and free swelling and increased the shortterm compressive strength of the soil. Behavior of the compacted sulfate soils, with and without treatment, has been quantified using a unique model that was used to represent both linear and nonlinear responses. Also the model predications were compared with other published data in the literature. Compressive stress– strain relationships of the sulfate soil, with and without lime and fly ash, have been quantified using a nonlinear constitutive model. The constitutive model parameters were sensitive to the calcium sulfate content and the type of treatment. Compared to the fly ash treatment, the lime treatment reduced the strain at peak stress making the lime treated soil more brittle.

A. Mohammed  C. Vipulanandan (&) Center for Innovative Grouting Material and Technology (CIGMAT), Texas Hurricane Center for Innovative Technology (THC-IT), Department of Civil and Environmental Engineering, University of Houston, Houston, TX 77204-4003, USA e-mail: [email protected]

Keywords Calcium sulfate  Free swelling  Compaction  Compressive strength  Lime  Fly ash

A. Mohammed e-mail: [email protected]

1 Introduction In the past few decades, it has been reported that sulfate rich soils have become a challenge in

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engineering projects because of swelling and also chemically attacking the construction materials such as steel and concrete (Mitchell and Dermatas 1992; Petry and Little 1992; Kota et al. 1996; Rollings et al. 1999; Puppala et al. 2002). Sulfate heave distress problems have been reported in Texas, Nevada, Louisiana, Kansas, Oklahoma, and Colorado where lime, fly ash and cement have been traditionally used to treat the natural soils rich in sulfates (Kota et al. 1996; Rollings et al. 1999). Hunter (1988) indicated that lime treated sulphate bearing clay is risky even at relatively low sulphate concentrations. Based on short-term (1–30 days) studies it has been observed that treating the sulfate soils with calcium-based chemicals such as lime and ordinary Portland cement has resulted in increased heave (Mitchell and Dermatas 1992; Petry and Little 1992). Bell (1996) studied the linear shrinkage of montmorillonite clay with different percentages of lime additive and showed that the shrinkage decreased with the addition of lime, but the decrease was not a linear. The study also showed that the unconfined compression strength did not increase linearly with the addition of lime and excessive addition of lime actually reduced the strength. During this treatment, mineralogical and microstructural changes occurred, which lowered the plasticity and also enhanced the loadbearing capacity and enable soil compaction to higher density. Arabani and Veis (2007) observed that any increase in lime content beyond 6 % had a negligible effect on the compressive strength of a treated CL soil. However, an increase in lime content up to 6 percent resulted in a noticeable increase in compressive strength and the results reported are for 1 day of curing. Reaction of lime with alumino-silicate in clays, produced hydrated cementitious products that bonded to the soil particles and the results reported are for 7 and 28 days of curing (McCarthy et al. 2009). During this treatment, mineralogical and microstructural changes occurred, which lowered the plasticity and also enhanced the load-bearing capacity and enable soil compaction to higher density. Ramesh (2009) concluded that adding barium chloride to lime treated soil prevented the formation of ettringite and thaumasite in lime treated soils containing sulphate. Cokca (2001) used low calcium and high calcium fly ash to stabilize expansive CH soils. The study also included comparison with lime and cement treated

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soils. The results showed that a the soil treated with 20 % fly ash had nearly the same stabilizing effect on the swelling potential as a soil treated with 8 % lime. Nalbantoglu (2004) investigated the effectiveness of class C fly ash as a stabilizer to expansive CH soils and the results reported are for 28 days. This study showed that the plasticity index of high plasticity soils was reduced but the effect was minimal with low plastic soils. The study also found that fly ash was an effective method to reduce the swelling potential for one of the tested soil but had adverse effects with other soils. Little et al. (2010) stated that civil engineers are at times required to stabilize sulfate-bearing clay soils with calcium-based stabilizers. Deleterious heaving in these stabilized soils may result over time. Recently, the potential of polymer treatment on a sulfate CL soil was investigated and the polymer was effective in modifying the soil properties in less than a day (Mohammed and Vipulanandan 2014). According to the studies summarized in Table 1 on clay soils stabilized with lime and fly ash, most of the specimens were prepared and tested near optimum moisture content (OMC %) from 1 to 30 days of curing. Both 6 % lime and 10 % fly ash have been used to treat the soil (Tables 1, 2). Calcium components in the stabilizers such as lime, cement and fly ash are known to react with free alumina and soluble sulfates in the soils to form ettringite mineral a weak sulfate mineral that will undergo significant heaving when subjected to hydration. This heave, termed as sulfate-induced heave in the literature, is known to severely affect the performance of highways, runways, parking lots, residential and industrial buildings, and other earth structures built on fly ash and lime treated sulfate rich soils (Hunter 1988; Mitchell and Dermatas 1992; Petry and Little 1992; Rajendran and Lytton 1997; Rollings et al. 1999). The formation of ettringite mineral (Ca6(Al(OH)6)2(SO4)326H2O) in treated soils and its exposure to moisture variations from seasonal changes result in differential heaving, which in turn causes cracking of pavement structures built on the treated soils. If not addressed immediately, this heave will further deteriorate the structures to a condition where they need immediate and extensive rehabilitation (Mitchell and Dermatas 1992; Petry and Little 1992). Hence there is a need to develop relationships to quantify the effect of calcium sulfate on the behavior of treated and untreated soils.

OMC

Mainly OMC was used Up to 40 °C and 100 % humidity

OMC

40 °C

25 °C

OMC

OMC (25–40) °C

100 % humidity

OMC

Natural water content

OMC

100 % humidity

–

OMC Not specified

25 °C

Water content for the study Curing temperature, humidity

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2 Objectives The overall objective was to quantify the changes in the properties of a field CL soil contaminated with varying percentage of calcium sulfate up to 4 % (40,000 ppm). Also of interest was to investigate the treatment of sulfate contaminate soil with lime and fly ash. The specific objectives are as follows: 1.

1

–

Not specified

7,14 and 28

2

1–30 days

4

0, 5, 10, 15, 20

6 and 8

Mainly 6 % of lime and 10 % fly ash

14 and 28 0, 10, 18, 30

6

14 and 28

0, 5, 10, 15, 20

7 and 30 6

10

3 Materials and Methods

Fly ash

OMC optimum moisture content—(standard compaction) ASTM D698

Expansive and sulfate soils Fly ash and lime have been used Clay soils Remarks

Expansive clay CH, CL Aravind et al. (2011)

Expansive clay

Lime

CH Kumar et al. (2007)

Lime

Sulfate soil Clay

Expansive clay

Puppala et al. (2006)

Lime

Sulfate soil

CH Phani and Sharma (2004)

Fly ash (class C)

Clay Harris et al. (2004)

Soil Stabilization Fly ash (class C) Clay Acosta et al. (2003)

Roadway over soft subgrade

Sulfate soil Lime

Fly ash (class C)

CL

Clay

Sivapullaiah et al. (2000)

3.

3.1 Soil

Edil et al. (2002)

Stabilizer Soil type Reference

Table 1 Summary of clay soils stabilized with lime and fly ash

Application

% of Stabilizer (by dry weight)

Curing time (days)

2.

Identify the changes in the soil clay mineralogy due to calcium sulfate contamination and treatment with lime and fly ash. Quantify the changes in the index properties, compaction properties, free swell and compressive strength of a CL soil with vary amount of calcium sulfate with and without treatment. Quantify the compressive stress–strain relationship of clay soil contaminated with calcium sulfate up to 4 %, and treated with 6 % lime and 10 % fly ash.

Field clay soil sample was used in preparing the sulfate soil. Atterberg limits, grain size distribution and hydrometer, compaction, swelling and compressive strength tests were performed according to ASTM Standard. The results are summarized in Table 3. 3.2 Hydrated Lime Lime for soil treatment applications is typically used in the form of quicklime (CaO) or Hydrated lime (Ca(OH)2). Quicklime (CaO) is manufactured by chemical processes transforming calcium carbonate (limestone—CaCO3) into calcium oxide (CaO). When quicklime reacts with water it transforms into hydrated lime. The hydrated lime (Ca (OH)2) reacts with the clay particles and modifies the clay based on its mineralogy. 3.3 Fly Ash Class C ASTM C618-91 defines fly ash as the finely divided residue that results from the combustion of ground or powdered coal and is transported from the boiler by

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Geotech Geol Eng Table 2 Literature review on sulfate soil stabilization using lime Reference

Soil type

Lime (%)

Sulfate content (ppm)

Mitchell (1986)

Silty clay

4

Up to 15,000

Hunter (1988)

Silty clay

4.5

43,500

Perrin (1992) Perrin (1992)

Clays Clays

5 6–9 %

2000–9000 14,000–25,000

Mitchell and Dermatas (1992)

Sand mixed with 30 % clay content

3

3000–62,000

Rajasekaran et al. (1994)

Marine clay with 52 % clay fraction

3

30,000

McCallister and Tidwell (1997)

Expansive clays

NA

2775

Sridhran et al. (1995)

Black cotton soil

6

5000–30,000 [12,000

Kota et al. (1996)

Clayey subgrades

6–7 %

Burkart et al. (1999)

Clays

6–9 %

233–18,000

Remarks

Mainly clay soils

Lime content varied between 3 and 9 %

Sulfate content varied between 223 and 30,000 ppm (0.023–3 %)

Table 3 Test methods and physical properties of the CL soil Property

Test method

Value

Passing sieve #200 (%)

ASTM D 6913

64

Specific gravity

ASTM D 854

2.66

LL (%) PI (%)

ASTM D 4318 ASTM D 4318

40 19

ASTM D 698

16.5

OMC (%) (standard compaction) 3

Max. dry density (g/cm )

ASTM D 698

1.52

Sand (%)

ASTM D 6913

36

Silt (%)

ASTM D 6913

45

Clay (%)

ASTM D 6913

19

Free swelling (%)

ASTM D 4546

7.0

Compressive strength (kPa)

ASTM D 5102

573

Soil type

ASTM D 2487

CL

then mixed with different percentage of calcium sulfate and water. Soil samples were placed in moisture tight bags and cured for 7 days at room temperature before testing. Four tests, Atterberg limits, compressive strength, standard compaction and swell tests were conducted on contaminated soil with different percentages (by weight) of calcium sulfate up to 4 %. Sulfate soils were treated separately with 6 % of lime and 10 % of fly ash. Based on the compaction results, optimum moisture content was used to prepare soil specimen for the strength, swell and shrinkage tests. Cylindrical specimens (1.400 dia. 9 2.800 length) were used for UCS tests. After 7 days of curing, treated soil specimens were subjected to unconfined compression strength (UCS) and free swell tests. 3.4.1 XRD Analysis

flue gases. The physical and chemical characteristics of fly ash vary greatly and mainly depend on the combustion method, coal properties, and particle shape of the fly ash. According to the literature, coal from different sources will produce different combustion products and these differences will influence the effectiveness of fly ash as a soil stabilizer (Karim et al. 2011). 3.4 Test Methods Soil was first dried in the oven at a temperature of 60 °C, crushed, pulverized and sieved to get sizes finer than # 4 (0.075 mm) sieve. The pulverized soil was

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An X-ray diffraction (XRD) analyses was performed in order to determine the effect of calcium sulfate contaminated and treatment with lime and fly ash. X-ray diffraction (XRD) was used to characterize the field soil and reaction products of soil with 4 % calcium sulfate and treated contaminated soils with 6 % of lime and 10 % of fly ash at 25 °C. The XRD pattern of the particles was obtained by using Siemens D5000 powder X-ray diffraction (Jenkins and Snyder 1996) (Fig. 1). Specimens for XRD were prepared from air-dried soils and ground with a mortar and pestle until the material passed through sieve No. 200 (75 lm). The powder (&2 g) was placed in an acrylic sample holder (3 mm)

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depth. All samples were analyzed by using parallel beam optics with CuKa radiation at 40 kV and 30 mA. Samples were ground to a fine texture using a mortar and pestle and were mounted on plastic sample holders. The average grain size of the soil crushed with an agate mortar and pestle is expected to be in the 10–15 lm range. All samples were scanned for reflections (2h) from 0° to 80° in steps of 0.02° and a 2 s count time per step. 3.4.2 Free Swelling Test (FS) The optimum water contents of clay soil contaminated with different percent of calcium sulfate with and without 6 % lime and 10 % fly ash treatment were determined by standard proctor tests in accordance with ASTM D 698. For cyclic free swelling tests, cylindrical samples were prepared at optimum water content for the natural clay soil and clay soil treated using 6 % lime and 10 % fly ash. The swelling tests were carried out in the conventional oedometer apparatus for natural soils and treated soils using lime and fly ash. The consolidation ring was pushed through the compacted soil samples at optimum moisture content, using standard proctor and the extra material was carefully trimmed in accordance with the ASTM Test Method D 2435-96 to match the height of the consolidation ring. The inside of the ring was lubricated with silicone grease to minimize side friction between the ring and the soil specimen. After 7 days curing period at 100 % humidity and 25 °C temperature, the swelling tests were performed based on ASTM D 4546. Filter papers were placed on top and bottom of the soil specimen to prevent finer particles from being forced into the pores of the porous stones placed on both sides of the specimen. Soils trimming were used to obtain the moisture content data of the specimens before start of the test. Each ring was weighed to cross check the maximum dry unit weight. The specimens were inundated with water and were allowed to swell freely under 7 kPa (1psi) pressure. Free swell measurements for first day were made at various time intervals similar to that used for consolidation test (ASTM D 4546-08). Each test was performed for at least 7 days. Times versus swelling measurements were then recorded. The percent free swell may be expressed as:

 FS% ¼

DH Ho

  100

ð1Þ

where: DH is height of swell due to saturation; Ho is the original height of specimen. 3.4.3 Unconfined Compression Tests (UCS) Unconfined compression tests were conducted according to ASTM D-5102. The unconfined compressive strengths were determined from the stress–strain relationships. The natural soil contaminated with calcium sulfate up to 4 % and treated sulfate soils using 6 % of lime and 10 % of fly ash were compacted at optimum moisture content and maximum dry density in standard compaction molds. Thin wall cylindrical steel samplers (1.400 dia.* 2.800 length) were carefully pushed in- the standard compaction mold, the soil samples were then extruded using a hydraulic jack. Soils trimming were used to obtain the moisture content data of the specimens before starting the test. Soil samples were weighed to crosscheck the maximum dry unit weight. The specimens were cured for 7 days period at 100 % humidity and 25 °C temperature. Loading was continued until the load decreased with increasing strain, or until 20 % strain was reached (Fig. 1).

4 Modeling Hyperbolic relationship has been used to present the behavior of cement and polymer modification soils (Ata and Vipulanandan 1998; Usluogullari and Vipulanandan 2011; Mohammed and Vipulanandan 2014). Relationship between index properties, compacted soil properties, free swell strain and compressive strength of the sulfate-contaminated soil with and without treatments was investigated. Based on the inspection of the test data following relationship is proposed. Y  Yo ¼

X AþBX

ð2Þ

where, Y is the soil property with varying sulfate contaminating. Yo is the soil property without contamination with calcium sulfate (natural CL soil). A and B: are model parameters (Table 4). X is the calcium sulfate concentration.

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Fig. 1 XRD Pattern of: a natural CL soil. b Soil contaminated with 4 % calcium sulfate. c Soil contaminated with 4 % calcium sulfate treated with 6 % of lime. d Soil contaminated with 4 % calcium sulfate treated with 10 % of fly ash

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Fig. 1 continued

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Geotech Geol Eng Table 4 Model parameters for treated and untreated soils contaminated with calcium sulfate

Treatment

Soil property (Y)

Figure

Model parameters Yo

Untreated

6 % Lime

10 % Fly ash (C)

A

R2

B

LL

3a

40

0.04

0.05

0.94

PI

3b

19

0.04

0.06

0.92

OMC (%) cdmax. (g/cm3)

5a 5b

17 1.52

0.21 -6.45

0.20 -9.18

0.95 0.92

Free swell (%)

9

7.0

Compressive strength (kPa)

11

553.6

0.094 -0.0019

0.065

0.95

-0.002

0.88

LL

3a

37

0.285

0.0

0.97

PI

3b

15.7

0.085

0.069

0.95

OMC (%)

5a

18.4

0.84

0.0

0.98

cdmax. (g/cm3)

5b

1.64

-14.48

-7.26

0.82

Free swell (%)

9

5.54

0.223

0.240

0.89

Compressive strength (kPa)

11

716

-0.003

-0.002

0.91

LL

3a

31.5

0.282

0.0

0.92

PI

3b

12

0.079

0.044

0.94

5a

20

0.802

0.0

0.95

cdmax. (g/cm )

5b

1.59

-9.278

0.94

Free swell (%)

9

5.85

Compressive strength (kPa)

11

807.4

OMC (%) 3

-10.64 0.181

0.172

0.91

-0.002

-0.002

0.96

5 Results and Analyses 5.1 XRD

Fig. 2 Modeling the linear and non linear responses of treated sulfate soils

Based on the experimental results the trends were either linear or nonlinear with the calcium sulfate content. As shown in Fig. 2 relationship proposed in Eq. 2 can be used to represent various linear and nonlinear trends based on the values of the parameters A and B. When parameters A and B are positive the relationship was hyperbolic. Linear relationship is represented by Eq. 2 when B = 0 and A will take any value. When parameters A and B are negative the inverse hyperbolic relationship is obtained.

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The soil had calcium silicate (CaSiO3) (2h peaks at 26.33°, 35.12°, 36.20° and 73.53°), aluminum silicate (Al2SiO5) (2h peaks at 39.55°, 57.19° and 60.09°), magnesium silicate (MgSiO3) (2h peak at 43.17°) and quartz (SiO2) (2h peaks at 14.02°, 20.92°, 27.98°, 45.87°, 64.21°, 68.36° and 75.68°). Addition of 4 % calcium sulfate modified the clay composition with the formation of ternesite (Ca5(SiO4)2SO4) (2h peaks at 20.85°, 28.43° and 29.88°) and aluminum silicate sulfate (Al5(SiO4)2SO4) (2h peaks at 40.03° and 60.09°) and merwinite (Ca3Mg(SiO4)2) (2h peak at 46.0°). XRD analyses also showed that the fly ash class C composition was quartz (SiO2), mullite (Al2O3SiO2), aluminum oxide (Al2O3), iron oxide (Fe2O3), calcium silicate (Ca2SiO4) and magnesium silicate (Mg2SiO4). The major quartz peaks were found at 2h of 19.75°, 20.92°, 23.23°, 27.59° and 50.21°. The main mullite peaks were at 2h of 12.77°, 31.21°, 35.16°, 55.12°, 60.09° and 63.83°. Duchesne and Reardon (1999) also reported mullite (Al2O3SiO2) peak for fly ash in their study. Addition of lime to

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(a) 75

(b) 50 No. of Data=19

Puppala (2004) Harris (2008) Cerato (2011)

45

65

Arvind (2007) Chakkrit (2008) Current Study

40

PI (%)

LL (%)

35 55

45

30 25

Sivapullaiah (2002) Harris (2004) Cerato (2011) Model

35

Puppala (2004) Chakkrit (2008) Current Study

20 15

25

No.of Data=17

10 0

1

2

3

4

Calcium Sulfate Concentraon (%)

5

0

1

2

3

4

5

Calcium Sulfate Concentraon (%)

Fig. 3 Variations of index properties with calcium sulfate content. a Liquid limit (LL). b Plasticity Index (PI)

sulfate contaminated soil resulted in the formation of ettringite which is hydrous calcium aluminum sulfate mineral [Ca6Al2(SO4)3(OH)1226H2O)] (2h peaks at 9.01°, 22.06°, 27.62°, 35.04°, 37.45° and 75.48°), calcium silicate hydrate (CaH2O4Si) (2h peaks at 39.7°, 42.7° and 46.0°) and aluminum silicate hydrate (AlSiO3H2O) (2h peak at 60.0°). 5.1.1 Liquid Limit (LL) Additional of calcium sulfate to the natural CL soil increased the liquid limit and the change was nonlinear as shown in Fig. 3a. When the calcium sulfate content in the soil was 4 %, the liquid limit increased from 40 to 57 % and can be attributed to the changes in the clay mineralogy. The change in the LL with calcium sulfate concentration was represented using hyperbolic relationship Eq. (2) and the parameters A, B and Yo are summarized in Table 4, and the coefficient of determination (R2) for the relationship was 0.94. Total of 19 data were collected from the literature and the liquid limit varied from 31 to 73 % with a mean and standard deviation of 52.3 % and 13.2 respectively. The collected data from the literature are compared to the model prediction and 47 % of these data located above the model prediction as shown in Fig. 3. Addition of 6 % of lime and 10 % of fly ash to the sulfate soil with 4 % of calcium sulfate decreased the liquid limit by 12 and 22 % respectively. Linear trends were observed between the LL and calcium sulfate concentration of sulfate soils modified using 6 % of lime and 10 % of fly ash (by dry weight) as shown in Fig. 4 (a). Fly ash treatment showed greater reduction in LL than lime treatment. The model parameters for lime and fly ash treatment are summarized in Table 4 with parameter B

being zero and the coefficient of determination (R2) were 0.97and 0.92 respectively. 5.1.2 Plasticity Index (PI) Plasticity index of natural CL soil increased from 19 to 34 % by increasing calcium sulfate content to 4 % because of the formation of calcium silicate sulfate and aluminum silicate sulfate in the soil. Total of 17 data were collected from various research studies in the literature and the plasticity index varied from 14 to 48 % with a mean and standard deviation of 22.2 and 11.3 respectively. About 65 % of the research data located below the model prediction as shown in Fig. 3b. Plasticity index of the natural soil contaminated with 4 % of calcium sulfate decreased by 25 and 16 % when the sulfate soil modified using 6 % of lime and 10 % of fly ash (by dry weight) respectively as shown in Fig. 4b. In this study, total of 21 soil samples were tested. Hyperbolic relationship was used to relate plasticity index to calcium sulfate concentration for treated and untreated sulfate soil as shown in Fig. 4b. The parameters A, B and Yo for untreated sulfate soil and treated using 6 % of lime and 10 % of fly ash are summarized in Table 4. The coefficients of determination (R2) for the hyperbolic relationships for untreated and lime and fly ash treated sulfate soils were 0.92, 0.95 and 0.94 respectively. 5.1.3 Compacted Soil Optimum moisture content for the field CL soil increased from 17 to 21.8 % when the calcium sulfate concentration increased from 0 to 4 % as shown in Fig. 5a. Total of 17 data on optimum moisture content

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(a) 65

(b) 40

60 35 55 30

45

PI (%)

LL (%)

50

40

25

Field Soil 6% lime 10% Fly ash Model

35 30 25

Field Soil 6% lime 10% Fly ash Model

20 15

20

10 0

1

2

3

4

5

0

Calcium Sulfate Concentraon (%)

1

2

3

4

5

Calcium Sulfate Concentraon (%)

Fig. 4 Variations of Index properties of untreated and treated calcium sulfate soil with 6 % of lime and 10 % of fly ash. a Liquid limit (LL). b Plasticity Index (PI)

(b) Maximum Dry Density (gm/cm3)

Opmum Moisture Content (%)

(a) 28 No.of Data=17

26 24 22 20 18 16

Harris (2008) Cerato (2011) McCarthy (2012) Model

14 12

0

1

2

Michael (2011) McCarthy (2012) Current Study

3

4

5

Calcium Sulfate Concentraon (%)

2

Gerald (2000) Michael (2011) McCarthy (2012)

1.9 1.8

Harris (2008) Cerato (2011) Current Study

1.7 1.6 1.5 1.4 1.3 1.2

No.of Data=16 0

1

2

3

4

5

Calcium Sulfate Concentraon (%)

Fig. 5 Variations of compacted soil properties with calcium sulfate content. a Optimum moisture content (OMC). b Maximum dry density

(OMC) for sulfate contaminated soils from various research studies were obtained and the mean and standard deviation were 20 and 4.5 %respectively. About 33 % of the literature data were located below the model predication as shown in Fig. 5a. Additional of 6 % lime and 10 % of fly ash (by dry weight) to the sulfate soil with 4 % of calcium sulfate in the current study increased the (OMC) by 6 and 12 % respectively as shown in Fig. 6a. Linear trends were observed between the (OMC %) versus calcium sulfate concentration for soils treated with 6 % of lime and 10 % of fly ash (by dry weight) as shown in Fig. 5a and the parameter B was zero. The model parameters A, B, Yo and coefficient of determination (R2 [ 0.9) for untreated sulfate soil and treated with 6 % of lime and 10 % of fly ash are summarized in Table 4. As shown in Fig. 5b, when the calcium sulfate concentration increased from 0 to 4 % the dry density of

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the CL soil decreased by 7 %. Total of 16 data on maximum dry density of calcium sulfate contaminated soils were collected from the literature and the mean and standard deviation were 1.66 g/cm3 and 0.11 respectively. All the data from the literature were located above the results from the current study as shown in Fig. 5b. In the current study, the maximum dry density of sulfate soil with 4 % calcium sulfate concentration increased 7 and 6 % by using 6 % lime and 10 % of fly ash respectively as shown in Fig. 6b. The model parameters A, B, Yo and coefficient of determination for untreated sulfate soil and treated with 6 % of lime and 10 % of fly ash are summarized in Table 4. 5.1.4 Free Swelling (FS) Total of 15 soil samples were tested in this study. Percent of free swelling with time for the CL soil with

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(b) Maximum Dry Density (gm/cm3)

Opmum Moisture Content (%)

(a) 26 24

22

20

Field Soil 6% Lime

18

10% fly ash Model

1.65 Untreated Soil 6% Lime 10% Fly ash Model

1.6 1.55 1.5 1.45 1.4 1.35

16 0

1

2

3

4

5

0

1

Calcium Sulfate Concentraon (%)

2

3

4

5

Calcium Sulfate Concentraon (%)

Fig. 6 Variations of compaction characteristics of treated soils with different calcium sulfate content. a Optimum moisture content (OMC). b Maximum dry density

different percentage of calcium sulfate are shown in Fig. 7. Free swelling percent of natural CL soil increased by 160 % when the calcium sulfate changed from 0 to 4 % as shown in Fig. 7 because of changes in the clay mineralogy. Free swelling versus calcium sulfate concentrations were compared with the several data from literature as shown in Fig. 8. About 50 % of the literature data were located above the model predication as shown in Fig. 8. Additional of 6 % of lime and 10 % of fly ash decreased the free swelling at 4 % of calcium sulfate concentration by 53 and 46 % respectively as shown in Fig. 9. Hyperbolic relationship between the percentage of free swelling and calcium sulfate concentration for untreated and treated sulfate soils were observed as shown in Fig. 9. The model parameters A, B and Yo are summarized in Table 4 and the coefficient of determination (R2) varied from 0.89 to 0.95. 5.1.5 Stress–Strain Relationship Stress–strain relationships for untreated and treated sulfate soils are shown in Fig. 10. With the increase in sulfate content the unconfined compressive strength and the initial modules of the treated and untreated compacted soils decreased as shown in Fig. 10. Total of 15 unconfined compression tests were performed in this study. Compressive strength of the CL soil used in the current study decreased by 65 % when the calcium sulfate content was increased from 0 to 4 % as shown in Fig. 11. The variation of strength with calcium sulfate content was represented using the

proposed model and the parameters are summarized in Table 4. Additional of 6 % of lime and 10 % of fly ash (by dry weight) to the sulfate soil with 4 % calcium sulfate increased the 7 days cured unconfined compressive strength by 130 and 120 % respectively as shown in Fig. 11. 5.1.6 Stress–Strain Behavior Modeling Soils are generally modeled as linear elastic, linear elastic—perfectly plastic or as strain hardening materials. In this study the soil, with and without treatment, exhibitored strain softening behavior as shown in Fig. 10. 5.2 p–q Model Based on experimental results, model proposed by Mebarkia and Vipulanandan (1992), was used to predict the stress–strain behavior of treated sulfate contaminated CL soil with different percentage of polymer solution (Eq. 3). The model is defined as follows: 1 0 B r¼B @

e ec

q þ ð1  p  qÞ

  e ec

þp

C C  rc  pþq A p

ð3Þ

e ec

where, r = compressive strength, rc ; ec = compressive strength and corresponding strain, p,q = material parameters.

123

Geotech Geol Eng

(a)

(b) 10 20

8

Free Swelling ( %)

16

Free Swelling (%)

6% Lime

9

Untreated Soil

18

14 12 10 8 6

Calcium Sulfate Concentraon 0% 1% 2% 4%

4 2

7 6 5 4 3

Calcium Sulfate Concentraon

2

0%

1%

2%

4%

1

0

0 0

2

4

6

8

10

12

0

2

4

(c)

6

8

Time (Days)

Time (Days) 12

10% Fly Ash

Free Swelling (%)

10 8 6

Calcium Sulfate Concentraon

4

0%

1%

2%

4%

2 0 0

1

2

3

4

5

6

7

8

Time(Days)

Fig. 7 Free swell–time relationships. a Untreated calcium sulfate soil. b Modified soil using 6 % of lime. c Modified soil using 10 % of fly ash

45

20

Lile (2010) Cerato et al. (2011) McCarthy (2012) Current Study Model

Free Swelling (%)

35 30

Free Swelling % at 7days

18

Untreated Soil

16

Free Swelling ( %)

40

25 20 15 10

6% Lime 14

10% fly ash Model

12 10 8

5

6

0 0

1

2

3

4

5

6

Calcium Sulfate Concentraon (%)

Fig. 8 Variation of free swell with calcium sulfate content

Parameter q was defined as the ratio of secant modulus at peak stress to initial tangent modulus. Parameter p was obtained by minimizing the error in the predicated stress–strain relationship. Hence, parameters p and q in (Eq. 3) were determined based on the stress–strain behavior of sulfate soil treated with

123

4

0

1

2

3

4

5

Calcium Sulfate concentration (%)

Fig. 9 Variation of free swell of sulfate soil after 7 days of curing with lime and fly ash stabilizer

6 % of lime and 10 % of fly ash and the values and coefficient of determination (R2) are summarized in Table 5. In the Fig. 10, the predicted values of compressive strength for sulfate contaminated CL soil

Geotech Geol Eng 900 700 600

700

Calcium Sulfate=1% Calcium Sulfate=4%

600

Model

Stress (kPa)

Stress (kPa)

500

(b) 6% Lime Treatment

800

Calcium Sulfate=0%

(a) Untreated Soil

400 300 200

500 400 300

Calcium Sulfate=0%

200

Calcium Sulfate=1% Calcium Sulfate=4%

100

100

0

Model

0 0

0.5

1

1.5

2

2.5

3

3.5

4

0

0.5

1

Axial Strain (%)

1.5

2

2.5

3

Axial Strain (%)

800 700

Stress (kPa)

600 500 400 300

Calcium Sulfate=0%

200

Calcium Sulfate=1% Calcium Sulfate=4%

100

(c) 10% Fly Ash Treatment

Model

0 0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Axial Strain (%)

Unconfined Compressive Strength (kPa)

Fig. 10 Compressive stress–strain relationship for a untreated sulfate soil, b treated sulfate soil with 6 % lime, c treated sulfate soil with 10 % fly ash

5.2.1 Parameter q

900

Untreated Soil

800

6% Lime 700

Parameter q represents the nonlinear behavior of the material up to peak stress. For calcium sulfate contaminated CL soil the parameter q was in the range of 0.56–1.0 (Table 5). Treating the CL soil with 6 % lime and 10 % fly ash decreased the q parameter to be in the range of 0.53–0.6 and 0.53–0.71 respectively (Table 5).

10% fly ash

600

Model

500 400 300 200 100 0 0

1

2

3

4

5

Calcium Sulfate Concentraon %

Fig. 11 Variation of compressive strength with sulfate content for untreated and treated sulfate contaminated CL soil

treated with 6 % lime are compared to the 10 % fly ash treated soil. The lime treated soils were stronger than fly ash treated soils. As summarized in Table 5 the parameters p and q influence by sulfate content and the method of treatment.

5.2.2 Parameter p For untreated soils the parameter p varied from 0.02 to 0.51. Soil treated with 6 % lime and 10 % fly ash the parameter p varied from 0.2 to 0.65 and 0.07 to 0.22 respectively. 5.3 Failure Strain The compressive strain at peak stress was affected by the level of sulfate contamination and also the type of

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Geotech Geol Eng Table 5 Stress–strain model parameters for sulfate soil treated using lime and fly ash Calcium sulfate, S (%)

Lime, L (%)

Fly ash, FA (%)

p–q Model parameter rc (kPa)

ec (%)

p

q

R2

0

–

–

573

2.77

0.22

0.69

0.99

1

–

–

285

1.88

0.51

0.56

0.99

4

–

–

196

3.72

0.02

1.0

0.99

0

6

–

810

1.33

0.22

0.53

0.97

1

6

–

533

1.49

0.47

0.60

0.98

4

6

–

450

1.94

0.65

0.58

0.98

0

–

10

715

2.69

0.22

0.53

0.99

1

–

10

494

3.10

0.41

0.64

0.99

4

–

10

433

3.81

0.07

0.71

0.97

Table 6 Nonlinear model parameters for sulfate contaminated CL soil treated with 6 % lime and 10 % fly ash Model parameters

Ao

a

b

c

d

e

f

R2

rc (kPa)

573

-2.81

0.26

240

0.16

8.9

1.2

0.96

ec (%)

2.77

0.65

0.21

-0.37

0.01

7E-5

4.2

0.94

p

0.22

0.08

0.22

0.02

1.13

0.5

2.3

0.85

q

0.69

0.10

0.62

2E-4

1.13

3E-4

1.0

0.83

treatment. Compared to the 10 % fly ash treatment where failure strain was over 2.5 %, 6 % lime treatment reduced the strain at failure stress to about 1.5 %. 5.4 Nonlinear Model (NLM) Parameters The model parameters rc, ec, p and q were influenced by the composition of the soil. It is being proposed to relate the model parameters to the independent variables [sulfate concentration (S%), lime (L%) and fly ash (FA%)] using a nonlinear power relationship as proposed by Demircan et al. (2011). The effect of sulfate content, lime and fly ash were separated as follows: Model parameters ðrc ; ec ; p; qÞ ¼ A0 þ a  ðSÞb þ c  ðLÞd þ e  ðFAÞf

In this study the effect of sulfate content on a CL soil was investigated. XRD analyses showed that the composition of clay was calcium silicate (CaSiO3), aluminum silicate (Al2SiO5), magnesium silicate (MgSiO3) and quartz (SiO2). Addition of calcium sulfate to the soil resulted in the formation of calcium silicate sulfate (Ternesite) and aluminum silicate sulfate. Over 140 tests were performed during this study. Also data from the literature was compared to the data from the current study. Based on the experimental and analytical study on a sulfate contaminated CL soil with and without treatment following conclusions are advanced. 1.

ð4Þ

where: Ao Initial model parameter for uncontaminated and untreated soil (field soil). a, b, c, d, e, f, g and h are the nonlinear model parameters. The NLM parameters were obtained from multiple regression analyses using the least square method. The NLM model parameters are summarized in Table 6.

123

6 Conclusions

2.

Liquid limit of natural CL soil increased from 40 to 57 % with the addition of 4 % calcium sulfate because of the modification of clay mineralogy. Adding 6 % lime and 10 % fly ash to the 4 % sulfate soil decreased the LL by 12 and 22 % respectively. Plasticity index of the CL soil increased by 79 with 4 % calcium sulfate content. The plasticity index for 4 % sulfate contaminated soil was

Geotech Geol Eng

3.

4.

5.

6.

7.

8.

9.

reduced by 25 and 16 % when treated with 6 % lime and 10 % fly ash respectively. Addition of lime and fly ash increased the maximum dry density and optimum moisture content of the compacted sulfate soils. Free swelling increased from 7 to 19 % with the increase of calcium sulfate content from 0 to 4 % because of the modification of the clay mineralogy. Additional of 6 % lime and 10 % fly ash decreased the free swelling percent to 9 and 10 % respectively after 7 days of swelling measurement. Compressive stress–strain relationship was affected by sulfate content in the soil. Unconfined compressive strength of the CL decreased with increased sulfate content. Addition of 4 % calcium sulfate to the soil decreased the strength by 65 %. The unconfined compressive strength of sulfate soils increased with 6 % lime and 10 % fly ash. The improvement in the soil strength due to lime and fly ash treatments can be attributed to the formation of calcium silicate hydrate as cementing compound. The hyperbolic model was effective in predicting the changes in the sulfate contaminated CL soil with and without treatment. Lime treatment (6 %) showed much higher enhancement in short-term strengths of sulfate contaminated soils compared to 10 % fly ash treatment. Also lime treatment reduced the compressive strain at failure stress to 1.5 % compared to fly ash treated soil of 2.5 %. Nonlinear compressive stress–strain model was used to predict the behavior of lime and fly ash treated sulfate contaminated soils. The model parameters were sensitive to the type of treatment.

Acknowledgments This study was supported by the Center for Innovative Grouting Materials and Technology (CIGMAT) with funding from various industries and Underground Construction Technology Association (UCTA). Sponsors are not responsible for any of the findings.

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