Applied Clay Science 52 (2011) 150–159

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Applied Clay Science

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Research Paper

Compressibility and permeability of Bangkok clay compared with kaoliniteand bentonite

Suksun Horpibulsuk a,⁎, Narongded Yangsukkaseam b, Avirut Chinkulkijniwat a, Yan Jun Du c

a School of Civil Engineering, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailandb Faculty of Engineering and Architecture, Rajamangala University of Technology, Suvarnabhumi, Thailandc Institute of Geotechnical Engineering, Southeast University, Nanjing 210096, PR China

⁎ Corresponding author. Tel.: +66 44 22 4322, +664607.

E-mail addresses: suksun@g.sut.ac.th, suksun@yahoo

0169-1317/$ – see front matter © 2011 Elsevier B.V. Adoi:10.1016/j.clay.2011.02.014

a b s t r a c t

a r t i c l e i n f o

Article history:Received 26 October 2010Received in revised form 8 February 2011Accepted 11 February 2011Available online 22 February 2011

Keywords:Bangkok clayKaolinBentoniteCompressionPermeability

The physical and engineering properties of remolded clays are intrinsic and can be used as a frame ofreference for the behavior of clay. Compressibility and permeability of remolded Bangkok clay at different ionconcentrations and valences were compared with kaolin and bentonite as representatives of non- and highswelling clays. Bangkok clay, a low-swelling clay, exhibited physical and engineering properties similar tothose of kaolin. The texture of coagulated Bangkok clay became a more flocculated structure with increasingion concentration and valence, resulting in higher water holding capacity and liquid limit. Even though thephysical properties of all tested clays varied significantly with pore water chemistry, the (PI, LL) points liedabove the A-line in the plasticity chart (where PI is the plasticity index and LL is the liquid limit) and could berepresented by a unique relationship. The change of the intrinsic compressibility and permeability with theconcentration and valence of the ions was interpreted by a generalized stress state e/eL. The lower e/eL valuewas associated with higher shear strength (resistance to vertical consolidation pressure in K0-consolidation)and lower permeability. As the ion concentration and valence were increased for both kaolin and Bangkokclay, the resistance to consolidation pressure increased and permeability decreased for the same void ratiodue to the decrease in e/eL. The liquid limit for bentonite decreased with increasing ion concentration andvalence due to the compression of the diffuse double layer. Hence, for the same void ratio, the resistance toconsolidation pressure decreased and permeability increased due to the increase of e/eL. Finally, relationshipsof the modified void index, I′v and consolidation pressure, σ′v, and generalized stress state e/eL andpermeability k were proposed. These relationships are useful and practical tools for assessing the intrinsiccompressibility and permeability of non- to high-swelling clays in terms of liquid limit, which is easilyobtained from conventional laboratory tests.

89 767 5759; fax: +66 44 22

.com (S. Horpibulsuk).

ll rights reserved.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Bangkok is situated on the 13,800 km2 Bangkok plain or the LowerCentral plain that lies between Ayutthaya and the Gulf of Thailand.The Bangkok plain is almost featureless with elevation ranging from 0to 2 meters above mean sea level (MSL). The Bangkok plain mergeswith a slightly higher alluvial plain at Ayutthaya.

The featureless topography of the Bangkok plain reflects the factthat it was covered by a shallow marine sea. Soft clay was depositednear the shore from 5000 to 3000 years ago. Duringmost of theMid toLate Holocene, the plain was a vast tidal flat that gradually subsidedresulting in a 0 to 20 m thick layer of Bangkok clay. The sea withdrewapproximately 2700 years ago and the soft clay was exposed at thesurface. The uppermost 2 m of clay was weathered over the past

2700 years (Nutalaya and Phienwej, 2002). The Bangkok plain couldbe viewed as a large bay fed by estuaries emerging from both thewestern mountain belt (Kanchanburi) and the neck of the Bangkokplain (near Ayatthaya). The contour of the thickness of Bangkok softclay is also presented in Fig. 1. Medium stiff and stiff to very stiff claysunderlay the soft clay. The stiff to very stiff clay is deposited above thefirst sand layer (1st sand) that sits over a hard clay. The Atterberg'slimits (LL and PL) of the stiff to very stiff and hard clays are practicallyidentical to each other, but they differ from those of the soft and themedium stiff clays. This is because the stiff to very stiff and hard clayswere formed near the end of the Pleistocence Epoch whereas the softand the medium stiff clays were formed during the Holocene. The softand the medium stiff clays are designated as Bangkok clay. The softBangkok clay is generally used as landfill and waste containmentlayer.

Ohtsubo et al. (2000) investigated the mineralogy and pore waterchemistry of Bangkok clay at a site that is 36 km east of Bang Na. TheBangkok clay profile consists of three zones. The middle zone (soft clay)is a marine clay, the upper zone (0 to 2.0 m depth) is a weathered clay

Fig. 1. Contour of thickness of soft Bangkok clay (Horpibulsuk et al., 2007).

151S. Horpibulsuk et al. / Applied Clay Science 52 (2011) 150–159

and the bottom zone (medium stiff clay) is an intertidal clay. The X-RayDiffraction (XRD) patterns of the Mg-saturated clay fraction (b2 μm)show that the clay fraction contains montmorillonite as the principalclaymineral with the range of 54 to 74%, followed by kaolinite andmica.Basedon thedifference in the sedimentvolumebetween theNa- andCa-clay fraction (b2 μm), the montmorillonite in Bangkok clay is classifiedas a high-swelling type. Cox (1968) mentioned that the presence ofmontmorillonite inBangkokclaywould characterize thehigh liquid limitandactivity. Numerous studies on theengineeringproperties of Bangkokclay were conducted (Agaki, 1981; Balasubramaniam, 1973, 1975;Bergado et al., 1990; Brenner et al., 1979;Horpibulsuk andRachan, 2004;Kim et al., 1994; Ladd et al., 1971; Suzuki, 1995).

Horpibulsuk et al. (2007) examined the physical and chemicalproperties of Bangkok clay from two different areas, Asian Institute ofTechnology (AIT) and Bangpee district, Samutpakarn province that arefar away and close to the Gulf of Thailand, respectively (vide Fig. 1). Theclay profile at AIT consists of weathered clay (0–2 m depth) andintertidal clay (2–8 m depth). The Na+, K+, Ca2+ and Mg2+ concentra-tions of the intertidal clay are almost constantwith depth and aremuchsmaller than those of sea water. At Bangpee, below the weathered clay,the Na+, K+, Ca2+ andMg2+ concentrations decrease significantlywithdepth. The difference in porewater chemistrywith depths and locationsis caused by leaching effect.

Physical properties of clays with different pore water chemistriesare mainly controlled by two distinct mechanisms (Sridharan and Rao,1975; Sridharan et al., 1986a,b, 1988) depending if the predominantclay mineral is either montmorillonite or kaolinite. The contribution ofdiffuse double layer to the physical properties dominates for montmo-rillonitic or swelling soils. The liquid limit of montmorillonitic soilsdecreases with the increase in ion concentration and valence due to thecompression of diffuse double layer. The increase in ion concentrationand valence for kaolinitic (non-swelling) soils enhances the coagula-tion; therefore explaining an increase of the shearing resistance andliquid limit. Kaolinite particles associate with each other in an edge-to-face manner when the attractive force is large and repulsive force issmall (van Olphen, 1963). An open flocculated structure has greatershear strength and water holding capacity.

Many studies addressed flow behaviors of bentonite and kaolindispersions (Abend and Lagaly, 2000; Brandenburg and Lagaly, 1988;Lagaly, 1989). Lagaly (1989) indicated that the effects of pH andcalcium ion in the clay-water system on flow curves of homoionicsodium bentonite and kaolin dispersions were different. The homo-ionic sodium bentonite particles would form card-house structurevia face (−)/edge (+) attraction in an acidic medium, or band-likestructure via face (−)/face (−) attraction in an alkaline medium.Therefore, flow behavior (yield stress) of the homoionic sodiumbentonite was different upon exposing to different pH conditions. Thechange in pore water chemistry affects not only the physicalproperties but also the engineering properties of remolded clay.

The engineering properties (shear strength, compressibility andpermeability) of remolded clay are intrinsic and can be used as aframe of reference for the behavior of natural sedimentary clays(Burland, 1990; Horpibulsuk et al., 2007; Nagaraj and Miura, 2001;Nagaraj et al., 1990, 1998). The intrinsic engineering properties ofremolded clay are mainly dependent on the generalized stress statee/eL (Horpibulsuk et al., 2004, 2007; Mitchell, 1996; Nagaraj andMiura, 2001; Nagaraj et al., 1993, 1995, 1998). Nagaraj and SrinivasaMurthy (1986) analyzed compression lines of different remoldedclays. They revealed that the compression lines can be normalized bythe void ratio at liquid limit, eL, and the normalized compression lineis called Intrinsic State Line, ISL represented by Eq. (1)

eeL

= 1:23−0:276 log σ′v ð1Þ

where e is the void ratio and σ′v is the effective vertical pressure (kPa).Based on the extensive data of 26 remolded clays compiled from the

literature, Burland (1990) proposed an Intrinsic Compression Line (ICL)for assessing the in-situ state of natural clays. The ICL is expressed byEq. (2)

Iv = 2:45−1:285x + 0:015x3 ð2Þ

80

90

100

152 S. Horpibulsuk et al. / Applied Clay Science 52 (2011) 150–159

where x=log σ′v. The void index is defined as:

Iv =e−e100ð Þ

Ccð3Þ

where e100 is the void ratio corresponding to σ′v=100 kPa and Cc isthe compression index. e100 and Cc can be approximated in terms of eLusing the following equations:

e100 = 0:190 + 0:679eL−0:089e2L + 0:016e3L ð4Þ

Cc = e100−e1000 = 0:256eL−0:04: ð5Þ

The ISL proposed by Nagaraj and Srinivasa Murthy (1986) and theICL by Burland (1990) reflect the same response. Horpibulsuk et al.(2007) showed that the compression curve of remolded Bangkok claycan be represented by Eq. (1).

Literature shows that for a particular clay, the clay fabric at anywater content (void ratio) is proportional to that at the liquid limit(Horpibulsuk et al., 2007; Mitchell, 1996; Nagaraj et al., 1993). Assuch, the permeability at any void ratio is proportional to that at theliquid limit void ratio and the permeability of any clay is dependent onthe generalized stress state e/eL. The permeability increases as e/eLincreases.

This study aims to investigate intrinsic properties of Bangkok clayfor different ion concentrations and valences compared with those ofkaolinitic and montmorillonitic clays to understand the mechanismscontrolling the physical and engineering properties of Bangkok clay. Apractical (simple and rational) method of assessing intrinsic com-pressibility and permeability characteristics of non- to high-swellingclays in terms of liquid limit is proposed. The proposed method isuseful for reclamation, landfill, and clay liner where remolded clay isused and its pore water chemistry may change with time.

2. Materials and methods

2.1. Soil samples

Bangkok clay samples were collected from the Asian Institute ofTechnology campus, Thailand at a depth of 2 to 3 m. The natural watercontentwas 76% and the groundwater levelwas at about 1 mbelow theground surface. Kaolin and bentonite, obtained from a commercialcompany, were used as representatives for non- and low-swelling clays,respectively. Physical properties of three soils are summarized inTable 1. The soil swelling potential of the tested clays was investigatedby the free swelling test proposed by Prakash and Sridharan (2004)because it is simple and predicts dominant clay mineralogy of soilssatisfactory (Horpibulsuk et al., 2007). The free swelling ratio, FSR, isdefined as the ratio of equilibrium sediment volume of 10 g of oven-dried soil passing a 425 μmsieve in distilledwater (Vd) to that in carbon

Table 1Basic properties of the tested clays.

Properties Kaolin Bentonite Bangkok clay

Specific gravity, G, 2.65 2.63 2.66Liquid limit, LL (%) 46 211 80Plastic limit, PL (%) 24 36 29Plasticity index, PI (%) 22 175 51Free swell ratio, FSR 0.7 3.9 12Sand (%) 0 0 0Silt (%) 31 52 39Clay (%) 69 48 61Cation exchange capacity (meq/100 g) 8 85 24pH 6.6 9.3 6.7Specific surface area (m2/g) 23 156 83

tetrachlorideorkerosene (Vk). Fig. 2 shows thegrain sizedistributionsofthe three clays.

Kaolin was composed of 0% sand, 31% silt and 69% clay. The specificdensity was 2.65 g/cm3. The liquid and plastic limits were 46% and24%, respectively. The clay was classified as low plasticity (CL) basedon the Unified Soil Classification System (USCS). The cation exchangecapacity and specific surface area were 8 meq/100 g and 23 m2/g,respectively. The FSR was 0.7 and classified as non-swelling accordingto Prakash and Sridharan (2004).

Bentonite was composed of 0% sand, 52% silt and 48% clay. Thespecific density was 2.63 g/cm3. The liquid and plastic limits were211% and 36%, respectively. It was classified as high plasticity clay(CH) with the cation exchange capacity and specific surface area of85 meq/100 g and 156 m2/g, respectively. The FSR was 3.9, which isclassified as high-swelling according to Prakash and Sridharan (2004).

Bangkok clay was composed of 0% sand, 39% silt and 61% clay. Thespecific density was 2.66 g/cm3. The liquid and plastic limits were 80%and 29%, respectively. It was classified as high plasticity clay (CH). Thecation exchange capacity and specific surface area were 24 meq/100 gand 83 m2/g, respectively. The FSR was 1.2, which is classified as low-swelling according to Prakash and Sridharan (2004).

Homoionic sodium and calcium clays were prepared by repeatedequilibration of the tested clays with the corresponding chloridesolutions (solid:solution ratio of 1:5) and with constant agitation forperiods ranging from 7 to 40 days. The excess salt solution was dis-carded by centrifugation and the dispersion was repeatedly washedwith distilled water, until the electronic conductivity of the dispersionwas close to that of water. The homoionized samples were air-dried,ball-milled to pass a 40 mesh British Standard sieve, and were storedin sealed polyethylene bags. The cation exchange capacity (CEC) ofthe tested clay specimens was determined by ammonium acetate(pH=7) exchange and subsequent determination of the exchange-able cation contents by standard methods (Hesse, 1972).

2.2. Methodology

2.2.1. Physical testsThe specific densities of the clay specimens were determined using

pycnometer as specified by the American Society for Testing andMaterials (ASTM) standard. The specific density values are an average ofthree tests; individual determinations differed from the mean by lessthan 0.01. The liquid limits of the clay specimens were determined byCasagrande's method. Using a mechanical device, liquid limit testswere carried out to secure a minimum of five points for plotting theflow curve. The consistency of the clay specimen was adjusted so that

0.00010.0010.010.10

10

20

30

40

50

60

70

Particle diameter (mm)

Perc

ent f

iner

KaolinBentoniteBangkok clay

Fig. 2. Grain size distribution of kaolin, Bangkok clay and bentonite.

0.00010.010.10

10

20

30

40

50

60

70

80

90

100

Perc

entf

iner

Particle diameter (mm)0.001

Ca0.001 M (Kaolin)Ca0.01 M (Kaolin)Ca0.0001 M (Bentonite)Ca0.001 M (Bentonitea)Ca0.01 M (Bangkokclay)Ca0.1 M (Bangkokclay)

Fig. 3. Effect of ion concentration on grain size distribution of kaolin, Bangkok clay andbentonite.

153S. Horpibulsuk et al. / Applied Clay Science 52 (2011) 150–159

the number of drops required to close the groove ranged between 15and 35. The entire operation was repeated for each specimen and theaverage of the two liquid limit values was determined. Variationbetween two trials was about 1%. The plastic limits of the clay speci-mens were determined as outlined in the ASTM procedure.

2.2.2. One-dimensional consolidation testsThe clays were tested in standard fixed ring consolidometers using

brass rings 6.0 cm in diameter and 2.0 cm high. The inside of the ringswas lubricated with silicon grease to minimize side friction betweenthe ring and the side specimen. The consolidation tests were con-ducted at constant 23 °C. The initial water contents for all tested clayswere fixed at 1.5 times the liquid limit. Themoist clay specimens werehand remolded in the consolidation rings, taking care to prevent anyair entrapment in the specimens. The consolidation ring was thenplaced on a porous stone. The top porous stone was carefully inserted.Filter papers were positioned between clay specimens and porousstones to prevent particles from being forced into the stones. Theporous stones were dampened to avoid adsorption of water fromthe specimen. The ring was next mounted in a consolidation cell,positioned in the loading frame under a pressure of 5 kPa and inun-dated with distilled water. Evaporation of water from the con-solidation cell was minimized by placing fitting metal jackets on topof the cell. Care was also taken to replenish any evaporated water.Conventional consolidation tests according to the ASTM standardwere carried out after equilibrium had been attained as indicated bythe nearly constant readings on the vertical dial gauge. The loadincrement applied was twice larger than the previous load. The dura-tion of each load was 24 h. The coefficient of permeability at averageeffective vertical stress for each load increment was determined bythe following equation:

k = cvmvγw ð6Þ

where k is the coefficient of permeability, cv is the coefficient ofconsolidation determined by rectangular hyperbola method proposedby Sridraran et al. (1987), mv is the coefficient of volume change andγw is the density of water.

3. Results

3.1. Physical properties

Table 2 shows the physical properties of Bangkok clay for differention concentrations and valences compared with those of kaolin andbentonite. The liquid limit of Na-kaolin increased from 54% in 0.001 MNaCl to 78% in 0.01 M NaCl. The liquid limit of Ca-kaolinte increased

Table 2Basic and chemical properties of kaolin, bentonite and Bangkok clay at different concentrat

Description of sample pH Specific surface area m2/g CEC (meq/

1. KaolinNa 0.001 M 6.6 – –

Na 0.01 6.5 – –

Ca 0.001 M 6.5 21 7Ca 0.01 M 6.4 28 10

2. BentoniteNa 0.0001 M 7.6 – –

Na 0.001 M 8.3 – –

Ca 0.0001 M 8.0 101 42Ca 0.001 M 8.7 87 32

3. Bangkok clayNa 0.01 M 6.8 – –

Na 0.1 M 6.7 – –

Ca 0.01 M 6.2 69 20Ca 0.1 M 6.5 78 26

from 59% in 0.001 M CaCl to 81% in 0.01 M CaCl. The increase in ionconcentration and valence in pore water coagulated the kaoliniteparticles, explaining the increase of shear resistance and liquid limit(Sridharan, 1991; Sridharan and Rao, 1975; Sridharan et al., 1988).The coagulation was also indicated by the aggregate size distribution(Fig. 3) and the greater specific density (Table 1). Both ion concen-tration and valence affected insignificantly the plastic limit, hence theplasticity index increased with ion concentration and valence. Theincrease in the liquid limit was associated with the increase in swel-ling potential (FSR) and activity, A.

In contrast to kaolin, the liquid limit of bentonite decreasedsignificantly as ion concentration and valence increased. For example,the liquid limit of Na-bentonite decreased from 131% in 0.0001 MNaCl to 126% in 0.001 M NaCl. The reduction of the liquid limit iscaused by the compression of diffuse double layer (Sridharan, 1991;Sridharan et al., 1986a,b). The particle size, FSR and activity of bento-nite decreased with increasing ion concentration and ion valence(Fig. 3 and Table 2). The possible soil fabric of kaolin and bentonite fordifferent ion concentrations and valences is illustrated in Fig. 4. Thechange in Atterberg's limits, particle size, FSR and activity with ionconcentration and ion valence for Bangkok clay and kaolin wassimilar. Even with changing liquid and plastic limits due to pore waterchemistry, the (PI, LL) plots of all tested clays still lied above the A-lineand were close to the relationship proposed by Horpibulsuk et al.(2007) (Fig. 5).

ions and valence.

100 g) FSR LL (%) PL (%) PI (%) Activity, A

– 54 26 28 –

– 78 27 51 –

0.7 59 26 33 0.50.7 81 28 53 0.7

– 131 26 105 –

– 127 26 101 –

12 129 26 103 2.30.6 102 24 78 1.9

– 71 28 43 –

– 100 28 72 –

0.7 77 29 48 0.812 105 29 76 1.1

Kaolin Bentonite

a a

b b

Fig. 4. Effect of ion concentration and valence on the clay fabric of kaolin and bentonite.

154 S. Horpibulsuk et al. / Applied Clay Science 52 (2011) 150–159

3.2. Compressibility

At the same void ratio, kaolin could sustain higher vertical con-solidation pressure when the ion concentration and valence increased(Fig. 6). At the same void ratio, the resistance to vertical consolidationpressure of bentonite decreased as the ion concentration and valenceincreased (Fig. 7). The relationships between void ratio and verticalconsolidation pressure in natural logarithmic scale for bentonite were

0 20 40 60 80 100 120 1400

20

40

60

80

100

120

A-Line, PI=0.73(LL-20)

Liquid limit, LL (%)

Plas

tici

ty in

dex,

PI

(%)

Na 0.001 M Na 0.01 M Ca 0.001 M Ca 0.01 M

KaolinNa 0.01 M Na 0.1 M Ca 0.01 M Ca 0.1 M

Bangkok clay

Na 0.0001 MNa 0.001 MCa 0.0001 MCa 0.001 M

Bentonite

PL = 0.79(LL-13)(Horpibulsuk et al., 2007)

Fig. 5. Effect of ion concentration and valence on the (PI, LL) relationship.

not linear. The change of the compression curve with ion concentra-tion and valence for Bangkok clay was similar to that of kaolin (Fig. 8).

The change of the resistance to vertical consolidation pressure withion concentration and valence for all tested clays could be explainedusing the generalized stress state parameter e/eL (Horpibulsuk et al.,2007; Nagaraj et al., 1990, 1998). Increase of ion concentration andvalence induces coagulation of both the kaolin and Bangkok clayparticles, increasing thewater holding capacity and liquid limit. Becausee/eL decreased at the same void ratio, the resistance to vertical con-solidation pressure and shear strength increased. On the other hand,the resistance to vertical consolidation pressure for bentonite decreased

100 101 102 103 1040.5

1.0

1.5

2.0

2.5

Kaolin0.001 M Sodium0.01 M Sodium0.001 M Calcium0.01 M Calcium

Consolidation pressure, 'v (kPa)

Voi

d ra

tio, e

σ

Fig. 6. Compressibility of kaolin for different ion concentrations and valences.

0

1.0

2.0

3.0

4.0

5.0

6.0

Bentonite0.0001 M Sodium0.001 M Sodium0.0001 M Calcium0.001 M Calcium

Voi

d ra

tio, e

100 101 102 103 104

Consolidation pressure, 'v (kPa) σ

Fig. 7. Compressibility of bentonite for different ion concentrations and valences.

10-8 10-70.5

1.0

1.5

2.0

Coefficient of permeability, k (cm/sec)

Voi

d ra

tio, e

KaolinNa 0.001MNa 0.01MCa 0.001MCa 0.01M

Fig. 9. e-log k relationships of kaolin for different ion concentrations and valences.

155S. Horpibulsuk et al. / Applied Clay Science 52 (2011) 150–159

with increasing ion concentration and valence because of the decreaseof e/eL.

3.3. Permeability

At the same void ratio, the permeability of kaolin decreased withincreasing ion concentration and valence (Fig. 9). For example, at a voidratio of 1.0, permeability decreased by 67%when both ion concentrationand valence increased from 0.001 M Na+ to 0.01 M Ca2+.

In contrast, the permeability of the bentonite increased with theion concentration and valence at the same void ratio (Fig. 10). Askaolin, the permeability of Bangkok clay decreased with increasing inion concentration and valence (Fig. 11).

Based on Horpibulsuk et al. (2007) and Nagaraj et al. (1993), thechange of permeability with ion concentration and valence can beexplained by the change of generalized stress state e/eL. For kaolin andBangkok clay (non- and low swelling clays), the generalized stress statee/eL decreased (since eL increased) with increasing ion concentrationand valence for the same void ratio, hence the permeability decreased.On the other hand, the increase of ion concentration and valenceincreased the generalized stress state e/eL (since eL decreases) forbentonite. As a result, the permeability increased even at the same voidratio.

0.5

1.0

1.5

2.0

2.5

3.0

Bangkok Clay0.01 M Sodium0.1 M Sodium0.01 M Calcium0.1 M Calcium

Voi

d ra

tio, e

100 101 102 103 104

Consolidation pressure, 'v (kPa) σ

Fig. 8. Compressibility of Bangkok clay for different ion concentrations and valences.

To conclude, the change of physical and engineering properties ofBangkok clay and kaolin with ion concentration and valence wassimilar. The mechanism controlling the physical and engineeringproperties is the different aggregate structures. The engineeringproperties of all tested clays can be explained by the generalizedstress state e/eL. Since PI and LL relations were similar for all testedclays, either PI or LL could be used to analyze the intrinsic com-pressibility and permeability characteristics. In this analysis, the liquidlimit, which is widely used in correlating physical properties toremolded engineering properties (Burland, 1990; Horpibulsuk et al.,2007; Nagaraj et al., 1998), was taken.

4. Analysis and discussion

4.1. Compressibility

Fig. 12 shows the compression curves of kaolin, bentonite andBangkok clay for different ion concentrations and valences and theirgeneralized stress state e/eL and consolidation pressure relationships.The e/eL versus log σ′v relationship for kaolin and Bangkok clay lied inthe same line and was represented by Eq. (1). The intrinsic com-pression index can therefore be approximated from 0.276eL. However,for the high swelling clay (bentonite) with a very high initial void

10-10 10-9 10-8 10-70.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Coefficient of permeability, k (cm/sec)

Voi

d ra

tio, e

BentoniteNa 0.0001MNa 0.001MCa 0.0001MCa 0.001M

Fig. 10. e-log k relationships of bentonite for different ion concentrations and valences.

10-9 10-8 10-70.5

1.0

1.5

2.0

2.5

3.0V

oid

ratio

, e

Bangkok clayNa 0.01MNa 0.1MCa 0.01MCa 0.1M

Coefficient of permeability, k (cm/sec)

Fig. 11. e-log k relationships of Bangkok clay for different ion concentrations andvalences.

I v

3.0

2.0

1.0

0

-1.0

-2.0

-3.0

High swell (Bentonite)

Low swell(Bangkok clay, Kaolin)

Iv 'v= 0.015log logσ 'vσ3-1.285log +2.450

Burland (1990)

100

101

102

103

104

Consolidation pressure, 'v(kPa)σ

Fig. 13. Void index versus log σ′v plots for kaolin, bentonite and Bangkok clay fordifferent ion concentrations and valences.

156 S. Horpibulsuk et al. / Applied Clay Science 52 (2011) 150–159

ratio, the e/eL versus log σ′v relationship was significantly differentfrom that of non- to low swelling clays (kaolin and Bangkok clay).

The same was found for the relationships between void index andlog σ′v of kaolin, bentonite and Bangkok clay for various ion concentra-tions and valences (Fig. 13). Iv versus log σ′vplots for kaolin and Bangkokclay could be approximated by Eq. (2). The equation was not applicablefor bentonite. Fig. 14 shows the relationship between e100−e1000 and eLfor the three tested clays at various ion concentrations and valences.

e/e L

Voi

drat

io, e

|r|=0.977Low swell (Bangkokclay , Kaolin)

e/eL 'v

Na 0.1MNa 0.01M

Ca 0.01MCa 0.1M

LLLL

70.6Na 0.01MNa 0.001M

Ca 0.001MCa 0.01M

99.677.3105.1

54.378.459.481.1

Bentonite

LLConcentration ConcentrationConcentration

Na 0.001MNa 0.0001M

Ca 0.0001MCa 0.001M

131.2126.7128.8101.8

100

101

102

103

1040

0.5

1.0

1.5

2.00.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Consolidationpressure, 'v(kPa)

Nagarajetal. (1998)e/eL

e/eL

High swell (Bentonite)

- 0.564log|r|=0.970

=1.893

=1.230 -0.276log

=1.206-0.260 log

σ

Kaolin Bangkok clay

σ

'vσ

Fig. 12. Compression curves of kaolin, bentonite and Bangkok clay for different ionconcentrations and valences and their generalization.

Eq. (5) as proposed by Burland (1990) fit the data for kaolin andBangkok clay but not the data for bentonite. However, e100 (void ratio at100 kPa consolidation pressure) for all tested clays could be approxi-mated from Eq. (4) as proposed by Burland (1990) (Fig. 15).

Even though ISL and ICL are applicable for non- to low swellingclays but not for all clay types, they are still widely accepted by manygeotechnical researchers because most natural clays are low-swellingclays. Non- to low-swelling soils are generally found in lowlands suchas Ariake bay in Japan (El-Shafei, 2001; Modmoltin, 2002) andBangkok clay (Horpibulsuk et al., 2007). Tanaka et al. (2001) alsoshowed that some marine clays (Pusan, Singapore, Drammen, andLouiseville clays) are classified as inactive and normal i.e. non- to low-swelling. Even though the soils contain montmorillonite, this claymineral might not be the dominant parameter controlling the soilexpansivity. The presence of other clay minerals, the amount of thenon-clay fraction (N0.002 mm) and the pore water chemistry can alsoplay a great role, masking the role of montmorillonite. It is possiblethat some clayey soils can be classified as non-swelling or lowswelling type, even though the clay mineral contains montmorillonite(Horpibulsuk et al., 2007).

In this study, we attempted to develop a generalized intrinsiccompression curve for all clay types (both non- and high-swelling)and for various conditions of pore water chemistry. The newly

e 100

-e10

00

0 1.0 2.0 3.0 4.00

1.0

2.0

eL

e100

- e1000 = 0.427eL -0.326

|r|=0.977Low swell (Bangkok clay, Kaolin)

Fig. 14. e100−e1000 and eL relationship for kaolin, bentonite and Bangkok clay fordifferent ion concentrations and valences.

KaolinBentoniteBangkok clay

0 1.0 2.0 3.0 4.00

1.0

2.0

3.0

eL

e 100

Fig. 15. e100 and eL relationship for kaolin, bentonite and Bangkok clay for different ionconcentrations and valences.

0

1.0

2.0

3.0

4.0

1.0 2.0 3.0 4.00

1.0

2.0

3.0

4.0

eL

KaolinBentoniteBangkokclay

e 100

-e10

00e 5

0

Fig. 17. Relationships between e50 and e50−e1000 versus eL for kaolin, bentonite andBangkok clay for different ion concentrations and valences.

157S. Horpibulsuk et al. / Applied Clay Science 52 (2011) 150–159

proposed parameter designated as modified void index, I′v is definedas:

I′v =e−e50

e50−e1000

� �ð7Þ

where e50 is the void ratio at 50 kPa vertical consolidation pressure.Fig. 16 shows the I′v− log σ′v plots for all the tested clays and for

various ion concentrations and valences. All points lied along thesame line. From the linear regression, the relationship between I′v andlog σ′v for 10 kPa ≤σ′v≤ 1280 kPa was presented in the form:

I′v = 0:029 logσ′v� �3−0:112 logσ′v

� �2−0:733 logσ′v� �

+ 1:427 ð8Þ

with a high degree of correlation of 0.981. e50 and e100−e1000 could beapproximated by eL using the following equations (vide Fig. 17):

e50 = 0:125e3L−0:727e2L + 2:265eL−1:059 for 1:44beLb3:45 ð9Þ

with a high degree of correlation of 0.988

e50−e1000 = 0:203e3L−1:185e2L + 2:864eL−1:889 for 1:44beLb3:45

ð10Þ

with a high degree of correlation of 0.980.

I v'

100

101

102

103

104

Consolidation pressure, 'v(kPa)σ

3.0

2.0

1.0

0

-1.0

-2.0

-3.0

Iv 'v= 0.029logσ 'vσ3-0.112log 'vσ-0.733log +1.427' 2

|r|=0.981

Fig. 16. I′v− log σ′v relationship for kaolin, bentonite and Bangkok clay for different ionconcentrations and valences.

Eqs. (7) to (10) are useful for many kinds of geotechnical workdealing with various remolded clay types subjected to different porewater chemistries such as land reclamation and waste containmentclay liners. Fig. 18 shows the predicted and themeasured compressioncurves of Kleinbekt Ton, Argile Plastique, London clay, Wiener Tegel,Magnus clay and Lower Cromer Till that were reported by Burland(1990). These clays have a wide range of liquid limit void ratios from0.663 to 3.521. The predicted curves are in very good agreementwith the measured ones. This figure confirms the application of theproposed equations for different clays.

4.2. Permeability

Based on Horpibulsuk et al. (2007), Mitchell (1996), and Nagarajet al. (1993), a generalized permeability relationship for non- to high-swelling clays was developed in the form (Fig. 19):

eeL

= 2:455 + 0:229 logk ð11Þ

100

101

102

103

104

Consolidation pressure, 'v(kPa)σ

40

30

20

10

Voi

d ra

tio, e

Predicted

Fig. 18. Predicted and measured compression curves.

10-10 10-9 10-8 10-7

Coefficient of permeability, k (cm/sec)

(a)

(b)

4.0

3.5

3.0

2.5

2.0

1.5

0.5

0

1.5

2.0

1.0

0.5

0

1.0

Voi

d ra

tio, e

e/e L

Fig. 19. e-log k relationships of kaolin, bentonite and Bangkok clay for different ionconcentrations and valences and their generalization.

158 S. Horpibulsuk et al. / Applied Clay Science 52 (2011) 150–159

where k is expressed as cm/s. This relationship fit all the test data andaccounted for the effect of swelling potential. The advantage of usingthis generalized stress state e/eL in analyzing permeability data is thatit can link with the consolidation pressure (Horpibulsuk et al., 2007;Nagaraj and Srinivasa Murthy, 1986; Nagaraj et al., 1998) and shearstrength (Srinivasa Murthy et al., 1988). This proposed equation isclose to the equation proposed by Nagaraj et al. (1993). All clayeysoils have the same permeability ranging between 10−7 cm/s ate=0.8eL and 10−9 cm/s at e=0.5eL. For a clay of known liquid limit,the change in permeability with consolidation pressure can thus beassessed from this generalized stress state and permeability relation-ship. Eq. (11) can also be used to derive the permeability of naturalclays because both remolded and natural samples exhibit the samepermeability as long as the void ratio is the same (Horpibulsuk et al.,2003, 2007; Nagaraj et al., 1995; Yamadera et al., 1998).

5. Determination of intrinsic compressibility and permeability

From the basic consideration discussed in this paper and the sub-sequent analysis, the practical (simple and rational) procedures forderiving the intrinsic compressibility and permeability of variousremolded clays in terms of liquid limit are summarized by the fol-lowing steps:

1. Determine index properties.2. Determine e50 and e50−e100 in terms of eL from Eqs. (9) and (10).3. Draw I′v− log σ′v relationship using Eq. (8).4. From e50, e50−e100 and I′v− log σ′v relationship obtained from

steps (2) and (3), draw e− log σ′v using Eq. (7).5. Use Eq. (11) to determine the permeability coefficient versus void

ratio.

6. Conclusions

The influence of pore water chemistry on the intrinsic (physical,compressibility and permeability) properties of Bangkok clay was

studied. The results were compared with kaolin and bentonite asrepresentatives of non- and high-swelling clays to understand themechanisms controlling the intrinsic properties. Conclusions can bedrawn as follows:

1. Bangkok clay was classified as a low-swelling clay. The texturebecame more flocculated structure with increasing ion concentra-tion and valence, enhancing the water holding capacity and liquidlimit. The aggregation was also indicated by the larger grain sizeand the greater specific density at higher ion concentration andvalence.

2. Despite changing physical properties with pore water chemistry,the (PI, LL) points for all tested soils still lied above A-line and wererepresented by a unique relationship. The intrinsic properties forvarious clay types and pore water chemistries were explained bythe generalized stress state e/eL.

3. The Intrinsic Compression Line (ICL) and the Intrinsic State Line(ISL) were applicable for non- to low-swelling clays, includingBangkok clay. To account for the effects of clay mineral and porewater chemistry, the generalized compression parameter wasintroduced and designated as modified void index, I′v. The I′v versuslog σ′v relationship was verified. This relationship is useful fordetermining the compression curves of various clays with differentpore water chemistries.

4. The generalized stress state e/eL was proven as the prime parameterdescribing the change in the permeability of all tested (non- to highswelling) clays with different pore water chemistries. A generalizedpermeability (e/eL versus log σ′v) relationship was proposed todetermine the permeability at different void ratios for a wide rangeof the swelling potential and pore water chemistry.

5. A method for determining the intrinsic compressibility and perme-ability of remolded clays was introduced in terms of the liquid limit.This method can be used as a practical tool for compressibility andpermeability analysis of various clay types encountered in geotech-nical practice, such as land reclamation, landfills, and vertical cutoffwall barrier. In these geotechnical works, clays are subjected tochanges of the pore water chemistry.

Notation

LL Liquid limitPL Plastic limitPI Plasticity indexICL Intrinsic Compression LineISL Intrinsic State Lineγw Density of waterσ′v Effective vertical stressCc Compression indexcv Coefficient of consolidatione Void ratioeL Liquid limit void ratioe50 Void ratio corresponding to effective vertical stress of 50 kPae100 Void ratio corresponding to effective vertical stress of 100 kPae1000 Void ratio corresponding to effective vertical stress of

1000 kPaIv Void indexI′v Modified void indexK Coefficient of permeabilitymv Coefficient of volume change

Acknowledgments

The authors would like to acknowledge the financial support,facility and equipment provided by the Suranaree University of Tech-nology. The last author appreciates the financial support from theNational Natural Science Foundation of China (Grant No. 40972173and 50878052).

159S. Horpibulsuk et al. / Applied Clay Science 52 (2011) 150–159

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