Effect of Pore–Fluid Chemistry on the Undrained Shear Strength of Xanthan Gum Biopolymer-Treated Clays

Chang, Ilhan; Kwon, Yeong-Man; Cho, Gye-Chun

doi:10.1061/(ASCE)GT.1943-5606.0002652

Open access

Technical Notes

Aug 27, 2021

Effect of Pore–Fluid Chemistry on the Undrained Shear Strength of Xanthan Gum Biopolymer-Treated Clays

Authors: Ilhan Chang, Ph.D., A.M.ASCE https://orcid.org/0000-0001-8369-0606 [email protected], Yeong-Man Kwon https://orcid.org/0000-0002-4719-1241 [email protected], and Gye-Chun Cho, Ph.D. [email protected]Author Affiliations

Publication: Journal of Geotechnical and Geoenvironmental Engineering

Volume 147, Issue 11

https://doi.org/10.1061/(ASCE)GT.1943-5606.0002652

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Abstract

Xanthan gum (XG) biopolymer-based soil treatment is an effective soil improvement method. In this study, we explored the effect of XG on the undrained shear strength of clays (kaolinite and montmorillonite) in chemically distinct pore fluids. Among the pore fluids tested, the undrained shear strength of kaolinite was the highest in kerosene, followed by deionized (DI) water and brine. This study hypothesized that the interparticle forces and interactions dominated the undrained shear strength of the kaolinite clay. In contrast, montmorillonite showed the highest undrained shear strength with DI water, followed by brine and kerosene, likely due to the increase in thickness of the viscous double layer that reduced the undrained strength of the montmorillonite clay. XG also affected the undrained shear strength of the clays, possibly due to the increase in viscosity of the pore fluids and modification of the clay interparticle fabrics. In DI water, XG increased the undrained shear strength of kaolinite (maximum shear strength was observed in the sample with an XG-to-soil mass ratio of 0.5%) via water absorption. Simultaneously, XG decreased the undrained shear strength of montmorillonite, likely due to XG-induced particle aggregation resulting from the changes in the montmorillonite particle surface charges. In 2-M-NaCl brine, the undrained shear strength increased with the increase in XG content, regardless of the mineral types, owing to the salt-induced double-layer compression and increase in concurrent XG-induced pore–fluid viscosity. However, the unaffected and constant undrained shear strength of both clays in nonpolar kerosene suggests that hydrating XG is a prerequisite for its application in soil treatment.

Introduction

Undrained shear strength (

s_{u}

) is an important geotechnical engineering design parameter for clayey soils in undrained conditions (e.g., submarine, offshore, glacial, and deep sediments), which is generally assessed by high shear rates and poor drainage conditions (Gutierrez et al. 2008; Kayabali and Tufenkci 2010). Despite several factors affecting the

s_{u}

of clays, the net derjaguin-landau-verwey-overbeek (DLVO) forces between clay particles (Warkentin and Yong 1962) and pore (or double-layer) fluid chemistry (Sridharan and Prakash 1999) are important factors affecting the

s_{u}

of clays.

Factors influencing the net DLVO forces among clays include clay mineralogy, plasticity, fabrics, pore–fluid chemistry, water content, stress history, anisotropy, and organics (Mayne 1985; Hyde and Ward 1986; Dolinar and Trauner 2007; Kayabali and Tufenkci 2010; Spagnoli et al. 2010; Hong et al. 2013). The net DLVO forces change the particle associations, thereby affecting the

s_{u}

of clays; the edge-to-face associations show higher

s_{u}

compared to other types of associations (i.e., edge-to-edge and face-to-face) because the Coulombic attraction between the oppositely charged edge and the face surface is significantly stronger than their van der Waals attraction (Dolinar and Trauner 2007). Furthermore, the collapse and reorientation of the edge-to-face contact result in a denser and more stable local geometry (Sachan and Penumadu 2007).

Pore–fluid chemistry can alter particle arrangements (e.g., flocculation and deflocculation); thus, it plays an important role in the

s_{u}

of clays. For example, salinity conditions affect the shear strength of soils, which experiences frequent changes in salinity due to freshwater or saltwater mixing (Schlue et al. 2010). Furthermore, the

s_{u}

of clays increases as the particle grain size decreases (i.e., the specific surface area increases) due to the larger water absorption capacity (Trauner et al. 2005).

Microbial biopolymers are polymeric biomolecules that are produced through the metabolism of microorganisms. Biopolymers contain side chains (e.g., trisaccharide) that can interact with charged clay particles, counterions, and pore water through hydrogen bonding (Chenu and Guérif 1991; Chang and Cho 2019; Chang et al. 2019). Thus, biopolymers have been reported as effective and ecofriendly soil modification materials owing to their ability to clog pore spaces (Khachatoorian et al. 2003; Bouazza et al. 2009; Chang et al. 2016a; Lee et al. 2019; Zhou et al. 2020) and enhance interparticle bonding between soil particles (Malik and Letey 1991; Kwon et al. 2017; Latifi et al. 2017; Chang et al. 2020; Soldo et al. 2020; Sujatha et al. 2020). Moreover, biopolymers have been shown to form viscous hydrogels and interact with the charged surfaces of clays (Chang et al. 2015, 2020). For instance, Sujatha et al. (2020) showed that xanthan gum (XG) biopolymer forms an interconnected network between the biopolymer molecules and soil surface, which results in a decrease in permeability and increase in strength. The interconnected network also resists compaction, resulting in a lower maximum dry density and higher optimal moisture content (Dehghan et al. 2019).

In addition, biopolymer-based soil treatments have been shown to significantly enhance the hydraulic erosion resistance of soils (Ham et al. 2018; Kwon et al. 2020), which is expected to effectively mitigate erosion or scouring problems of waterfront geotechnical engineering structures. Additional studies showed that biopolymer-induced soil flocculation accelerates the settling velocity and reduces the turbidity of soil suspensions (Kwon et al. 2017; Kang and McLaughlin 2020), which is useful for sludge dewatering (Guo and Wen 2020). Meanwhile, the redistribution of XG (i.e., from strong intergranular bridges to a uniform distribution around the grains) occurs during the wetting–drying cycles, which gradually reduces the overall shear strengthening effect of the biopolymer (Chen et al. 2019a). Singh and Das (2020) showed that biopolymer treatment reduces mass loss during repeated freeze–thaw cycles.

Biopolymer interactions with pore fluids and clay particles can improve the shear strength of soils, accompanied by an increase in the friction angle or cohesion (Khatami and O’Kelly 2012; Chang and Cho 2019; Chen et al. 2019b) via particle aggregation and the following conglomeration effect (Chang and Cho 2019); this would improve the erosion resistance of fine-grained soils (Ham et al. 2018; Kwon et al. 2020). However, the effect of the pore–fluid chemistry on the

s_{u}

of biopolymer-treated clays has not yet been investigated.

In this study, we explored the effect of the XG content, clay mineralogy, and pore–fluid type (deionized [DI] water, 2-M-NaCl brine, and kerosene) on the

s_{u}

of kaolinite and montmorillonite clays. The

s_{u}

of the XG-treated soils with different pore–fluid types and contents was evaluated through fall cone tests. The morphology of the clay particles in the presence of different pore fluids, ions, and XG was analyzed using scanning electron microscopy (SEM).

Materials and Methods

Characteristics of the Clay Materials

Kaolinite (1:1 type; Bintang, Indonesia) and montmorillonite (2:1 type, CAS: 1302-78-9; Sigma-Aldrich, Bellefonte, Pennsylvania) were used to examine and compare the effects of clay mineralogy on the

s_{u}

. Kaolinite has low swelling and reactive areas on its external surfaces because the basal oxygen atoms of the tetrahedral silica sheet and the hydroxyls of the octahedral alumina sheet are held together by hydrogen bonding (Giese 2003). Meanwhile, montmorillonite shows a high swelling potential upon water addition because its layers are loosely held together by van der Waals forces (Chen and Peng 2018).

Although kaolinite presents a larger particle size than montmorillonite, the latter exhibits a higher specific surface area (SSA), cation exchange capacity (CEC), and a thicker double layer, as shown in Table 1. Kaolinite presents a lower aspect ratio and a higher positive edge charge portion (Tombácz and Szekeres 2006; Villanueva et al. 2010), whereas montmorillonite contains approximately 90%–95% of pH-insensitive negative charges contributing to the total charge (Au and Leong 2016). Thus, the attraction between the edge and face charges is more critical to the

s_{u}

of kaolinite than in montmorillonite (Penner and Lagaly 2001).

Table 1. Index properties of the clays that were used in this study

Type of clay	$D_{50}$ (μm)	SSA ( $m^{2} / g$ )^a	CEC (meq/100 g)^b	pH^c	XG (%)	Deionized water		2 M NaCl		Kerosene
Type of clay	$D_{50}$ (μm)	SSA ( $m^{2} / g$ )^a	CEC (meq/100 g)^b	pH^c	XG (%)	PL (%)	LL (%)	PL (%)	LL (%)	PL (%)	LL (%)
Kaolinite	3	22	6.1	4.2	0	31	70	34	51	—	93
					0.1	35	74	36	52		93
					0.5	32	97	37	55		91
					1	40	80	33	61		84
					2	36	79	46	71		92
Montmorillonite^d	0.07	221	64.1	6.5	0	62	389	42	86	—	61
					0.1	54	386	46	96		60
					0.5	55	373	44	100		60
					1	71	370	43	106		58
					2	69	338	41	114		59

a

Specific surface area obtained by the methylene blue adsorption measurement (Santamarina et al. 2002).

b

Cation exchange capacity measured using the methylene blue cation exchange capacity (Inglethorpe et al. 1993).

c

Supernatant pH measured after settling sediment with 300% water content.

d

The chemical composition of the original montmorillonite is

{SiO}_{2}

,

{Al}_{2} O_{3}

,

{Fe}_{2} O_{3}

, CaO, MgO,

{TiO}_{2}

,

{Na}_{2} O

, and

K_{2} O

and loss of ignition (Anirudhan and Ramachandran 2007).

Montmorillonite clays have more negative zeta potential (i.e., the potential difference between the media and clay layers) than kaolinite minerals because they have more

{SiO}^{-}

groups on their surface, owing to their 2:1 structure (Doi et al. 2019). When salt (e.g., Na- or Cs-halide) is added, the negative zeta potential of kaolinite tends to be more negative owing to the formation of pH-dependent groups (Liu et al. 2012), whereas that of montmorillonite becomes neutralized by cation adsorption owing to the enhanced interlayer activity (Doi et al. 2019).

Prior to the experiments, kaolinite was washed six times with DI water to remove the supernatants after solid and fluid separation (Wang and Siu 2006), whereas montmorillonite was used without washing. The clays were dried in an oven (110°C) according to ASTM D2216-19 (ASTM 2019). The index properties of the clays used are listed in Table 1.

Characteristics of Xanthan Gum

XG is a biopolymer produced by Xanthomonas campestris; its structure consists of repeating glucose units and side chains with three sugar units (García-Ochoa et al. 2000). XG is water soluble, and once dissolved, its structure expands, and the side chains that consist of glucuronic and pyruvic acid groups become negatively charged (Hassler and Doherty 1990; Nugent et al. 2009; Petri 2015). Therefore, XG is widely used as a thickener and stabilizer for suspensions, solid particles, and foams in aqueous formulations (Katzbauer 1998; Chang et al. 2016b). XG has shown high potential for soil stabilization through the enhancement of its shear strength (Lee et al. 2017; Chang and Cho 2019) and compressive strength (Kwon et al. 2019) via clay–XG aggregation (Chang et al. 2019). Moreover, XG reduces the hydraulic conductivity of soil owing to pore clogging induced by XG hydrogels (Cabalar et al. 2017). A research-grade XG (CAS: 11138-66-2; Sigma-Aldrich, Saint Louis) was used in this study for the experiments.

Preparation of the XG–Clay Mixture

Washed and oven-dried clays were mixed with XG powder at mass ratios (

m_{b} / m_{s}

) of 0% (untreated), 0.1%, 0.5%, 1.0%, and 2.0%. Three chemically distinct pore fluids, namely DI water, 2-M-NaCl brine (high ionic concentration), and kerosene (low permittivity), were used, as in previous studies (Jang and Santamarina 2016; Cao et al. 2019). XG solutions were prepared by mixing these pore fluids with dry XG powder. Oven-dried clays and XG solutions were mixed until the formation of uniform XG–clay-pore fluid mixtures. We prepared 2-M-NaCl brine (i.e., two moles of NaCl per liter of DI water) by dissolving 58.44 g (1 mol) of NaCl (CAS No. 1310-58-3; Junsei Chemical Co., Tokyo) in 500 mL of DI water in a beaker using a magnetic stirrer to form 500 mL of a uniform 2-M-NaCl solution. During the experimental procedures, the fluid-to-dry soil ratio (

w = m_{w} / m_{s}

) was adjusted by adding the prepared pore fluids into the soils at gradual increments and thoroughly mixed using a laboratory spatula to obtain uniform soil samples. The liquid limit (LL) and plastic limit (PL) of the XG–clay mixtures in Table 1 were measured via laboratory fall cone tests (British Standards Institution 2017) and the thread rolling method (ASTM 2017), respectively.

Experimental Details and Testing Procedure

The

s_{u}

of clay was evaluated via laboratory fall cone tests (Wood 1990; Koumoto and Houlsby 2001; O’Kelly et al. 2018). The effect of the shearing rate on the

s_{u}

values obtained from the fall cone tests was not investigated in this study; however, differences in the shearing rates may have existed between the fall cone tests and could have nonnegligible influences on the obtained

s_{u}

values. Koumoto and Houlsby (2001) analyzed the strain effect on

s_{u}

by comparing laboratory triaxial test and fall cone test measurements;

s_{u}

was reported to have increased by 60% at high strain rates. Kulhawy and Mayne (1990) analyzed the triaxial compression data and observed a 10% increase in

s_{u}

per log cycle of the strain rate. In contrast, Chow et al. (2012) argued that the

s_{u}

measured with parallel plate rotational viscometer tests was smaller than that assessed using conventional triaxial tests owing to the viscous rate effect.

In this study, XG–clay mixtures were tamped into a container with a 55-mm diameter and 40-mm height. Soils with a degree of saturation higher than 90% were used. After surface trimming, the wet weight was measured to obtain the density information (e.g., dry density, total density, and void ratio) for each specimen. Simultaneously, a cone penetration test was conducted to prevent alterations in the specimen moisture contents. The 80-g and 30°-apex cone could penetrate the soil pastes for 5 sec. The

s_{u}

of the clay obtained from the fall cone test (

s_{u}^{FC}

) was calculated as follows:

s_{u}^{FC} = K \frac{w}{d^{2}}

(1)

where

K

= cone factor that reflects the friction effect between the cone and soil (Stone and Phan 1995);

W

= weight of the cone (80 g); and

d

= cone penetration depth (mm). A

K

value of 0.867 was adopted for the 30°-apex cone, which corresponds to

s_{u}^{LL} = 1.7 kPa

(

s_{u}^{LL}

is the

s_{u}

when

w = LL

) (Sharma and Bora Padma 2003; Kayabali and Tufenkci 2010). The

s_{u}

values of the soils with liquidity index [

LI = (w - PL) / (LL - PL)

] values greater than 0.2 were measured to avoid potential overestimations (Vardanega and Haigh 2014).

A laboratory vane shear test was performed simultaneously on untreated clays under the same conditions to obtain the vane shear strength (

s_{u}^{V}

) of untreated clays for comparison and verification. This was achieved using a rectangular vane (

width = 12.7 mm

,

height = 12.7 mm

, and thickness = 0.05 mm) with a rotation velocity of

60 ° / \min

according to ASTM D4648/D4648M-16 (ASTM 2016). For each XG–clay–water content (

w

) condition, fall cone and vane shear tests were conducted with three different specimens to obtain reliable average values for

s_{u}^{FC}

and

s_{u}^{V}

. After the measurements, the XG–clay-pore fluid samples around the cone and vane intrusion were collected and dried in an oven at 110°C for 24 h to obtain the

w

following ASTM D2216-19 (ASTM 2019).

The microstructures of the clays (untreated and XG-treated) were observed using SEM (S-4800 and SU-8230, Hitachi High Technologies, Tokyo). The clays were sampled at

w = LL

. The samples were air-dried at room temperature and attached to a 25-mm-diameter SEM mount with carbon conductive tabs (Pelco Tabs; Ted Pella, Redding, California). The specimens were coated with osmium (

{OsO}_{4}

) for 10 s under vacuum using a plasma coater (OPC-60A). Conventional SEM was conducted to observe the morphology in terms of the effect of XG and pore fluids on the clays. However, advanced microscopy techniques, such as environmental-SEM (Carrier et al. 2013) or cryo-SEM (Du et al. 2009), are needed to analyze the XG–clay–salt water interactions in moist conditions.

Correlations between $s_{u}$ and Index Properties

Koumoto and Houlsby (2001) suggested the following linear regression equation showing the relationship between log

s_{u}

and

\log w

:

s_{u} = {(\frac{w}{α})}^{- \frac{1}{β}}

(2)

where

α

= water content when

s_{u}

is 1 kPa; and

β

= slope of log

w

and

\log s_{u}

. In addition,

α

and

β

depend on the soil plasticity, compressibility, SSA, particle structure, pore–fluid chemistry, and organic matter content (Koumoto and Houlsby 2001; Trauner et al. 2005; Dolinar and Trauner 2007).

From Eqs. (1) and (2),

s_{u}

and LI can be correlated as follows (Wroth and Wood 1978; Wood 1990):

s_{u} = s_{u}^{LL} R^{(1 - LI)}

(3)

where

s_{u}^{LL}

= undrained shear strength at LL; and

R

= ratio between the

s_{u}

values at PL and LL. The

R

factor value depends on the clay mineral type and soil activity (Wood 1990). The correlation factors (

α

,

β

, and

R

) can be used to estimate the

s_{u}

of the clays, with

w

and the index properties (e.g., LL, LI) assessed in the laboratory.

Results and Analyses

Effect of Pore–Fluid Chemistry on the $s_{u} - w$ Relationship

This study investigated the differences in clay behaviors between water-based (DI water and 2-M-NaCl brine) and kerosene-based mixtures. In clay, the relative permittivity of the pore fluids affects the double-layer forces and accompanying clay fabrics (Espinoza and Santamarina 2012); moreover, the double-layer thickness increases with the relative permittivity of the pore fluids (Mitchell and Soga 2005). However, the van der Waals attraction forces related to the Hamaker constant decrease with an increasing pore–fluid relative permittivity (Sridharan and Rao 1979).

Fig. 1 shows the

s_{u} - w

relationship for the different clay types and pore fluids, and Fig. 2 presents the

α

and

β

variations of the XG-treated clays in terms of the pore–fluid relative permittivity variation based on the data from Fig. 1. The similar trends shown by

s_{u}^{V}

and

s_{u}^{FC}

for untreated clays with DI water [Figs. 1(a and d)] validate the fall cone tests conducted to assess the

s_{u}

of the clays.

Fig. 1. Variation of $s_{u}$ in (a, b, and c) kaolinite; and (d, e, and f) montmorillonite with water content and $m_{b} / m_{s}$ variation in (a and d) deionized water; (b and e) 2 M NaCl brine; and (c and f) and kerosene. Hollow symbols indicate $s_{u}^{FC}$ (undrained shear strength from fall cone test), whereas solid symbols indicate $s_{u}^{V}$ (undrained shear strength from the vane shear test) of the untreated clays with the deionized water.

Fig. 2. Variations of the parameters (a and c) $α$ ; and (b and d) $β$ with the relative permittivity of the pore fluids and xanthan gum content. The triangle symbols represent soils with kerosene. The rectangular and circular symbols are soils with 2 M NaCl brine and deionized water, respectively. The symbol colors darken from white to black as the xanthan gum content increases.

The

s_{u}

of kaolinite is affected by the net attractive forces between the clay particles, whereas that of montmorillonite is affected by the viscous resistance of the double layer (Sridharan and Prakash 1999). Among the different pore fluids, kaolinite shows the highest

s_{u}

[Figs. 1(a–c)] and highest

α

and

β

values [Figs. 2(a and b)] with kerosene, followed by DI water and brine, whereas montmorillonite shows the highest

s_{u}

with DI water, followed by brine and kerosene [Figs. 1(d–f) and 2(c and d)]. Generally, the attraction forces and particle fabrics govern the

s_{u}

of kaolinite (Warkentin and Yong 1962; Sridharan and Prakash 1999). Thus, kaolinite exhibited the highest

s_{u}

and shear parameters in kerosene, which has the lowest relative permittivity among the three pore fluids. This was due to the presence of edge charges and van der Waals forces, which induced interparticle interactions and consequently increased the

s_{u}

of kaolinite (Wang and Siu 2006). Interestingly, various studies have also observed that kaolinite shows an LL increase in nonpolar (low relative permittivity) pore fluids (Jang and Santamarina 2016; Chang et al. 2019).

In contrast, the thick viscous double layers mainly govern the shear resistance of montmorillonite (Warkentin and Yong 1962; Sridharan and Prakash 1999) owing to the high aspect ratio and 2:1 structure of montmorillonite, resulting in low net attraction forces (Secor and Radke 1985; Santamarina et al. 2001; Tombácz and Szekeres 2006). Thus, montmorillonite could have higher

s_{u}

[Figs. 1(d–f)],

α

, and

β

[Figs. 2(c and d)] values in fluids with higher permittivity.

Effect of Clay Mineralogy on the $s_{u} - w$ Relationship

While considering the effect of clay mineral type on the

s_{u}

, montmorillonite [Fig. 1(d)] required a much higher

w

than kaolinite [Fig. 1(a)] to achieve the same

s_{u}

in DI water owing to the high SSA of montmorillonite; this is in accordance with the findings by Sridharan and Prakash (1999). Because the

s_{u}

generally decreases as

w

increases, montmorillonite shows a higher

s_{u}

than kaolinite at the same

w

.

However, in 2-M-NaCl brine, the salt-induced double-layer suppression and particle rearrangement reduced the shear resistance of both clays (Sridharan and Prakash 1999). Kaolinite [Fig. 1(b)] and montmorillonite [Fig. 1(e)] showed a drastic

s_{u}

reduction compared to that in DI water [Figs. 1(a and d) and (2)], whereas montmorillonite had a higher

s_{u}

than kaolinite at a similar fluid (2-M NaCl) content. The double-layer compression caused by the cations appeared more prominent for montmorillonite because it presents a higher CEC and interlayer activity than in kaolinite (Doi et al. 2019).

In the absence of double-layer formation with nonpolar kerosene, kaolinite with a larger edge portion (Wan and Tokunaga 2002) shows higher

s_{u}

values than montmorillonite [Figs. 1(c and f) and (2)]. In kerosene, the

s_{u}

of the clay is mainly governed by the net attraction forces and fabrics instead of the viscous resistance of the double layers (Jang and Santamarina 2016) because the double-layer thickness of the clay decreases in kerosene (Dukhin and Goetz 2010).

Effect of XG on the $s_{u} - w$ Relationship

The XG treatment changes the shear resistance of the clays because the net negative charges on the XG branches can interact with the clay particles, salt ions, and water molecules (Chang et al. 2015; Turkoz et al. 2018). Water and salt adsorption by XG increases the

s_{u}

of the clays, whereas particle aggregation reduces the

s_{u}

owing to the decrease in clay surface area. Thus, kaolinite has more prominent variations in its shear resistance as compared to montmorillonite.

For kaolinite in DI water [Fig. 1(a)], the

s_{u}

peaked at

m_{b} / m_{s} = 0.5 %

and decreased at

0.5 % < m_{b} / m_{s} < 1 %

. In other words, kaolinite in DI water showed 50% and 70% increments in

α

and

β

values with 0.5% of XG, respectively [Figs. 2(a and b)]. A possible hypothesis is that for

m_{b} / m_{s} = 0 % - 0.5 %

, XG mainly absorbs the pore fluids instead of affecting the kaolinite fabrics (Nugent et al. 2009), which increases the pore–fluid viscosity (Milas et al. 1985) and

s_{u}

. However, for

0.5 % < m_{b} / m_{s} < 1 %

, XG aggregates the kaolinite particles (Nugent et al. 2009) and causes a subsequent decrease in the absorbed water (Chang et al. 2019) and

s_{u}

.

In contrast, the maximum

s_{u}

of montmorillonite in DI water was observed at

m_{b} / m_{s} = 0 %

; subsequently,

s_{u}

gradually decreased as

m_{b} / m_{s}

increased [Fig. 1(d)]. With the addition of 2.0% XG,

α

and

β

of montmorillonite in DI water decreased by 16% and 11%, respectively [Figs. 2(c and d)]. Because montmorillonite has a higher SSA and CEC than kaolinite, XG could facilitate XG–montmorillonite aggregation while interrupting viscous double-layer formation by montmorillonite particles within DI water (Rao et al. 1993; Laird 1997; Dontsova and Bigham 2005), thereby causing a progressive decrease in

s_{u}

with increasing

m_{b} / m_{s}

.

In brine, the

s_{u}

of both clays increased with increasing

m_{b} / m_{s}

[Figs. 1(b and e)], which may be attributed to the salt-induced double-layer compression and concurrent XG-induced pore–fluid viscosity increase (Turkoz et al. 2018). Kaolinite showed a 46% increase in

α

and 74% increase in

β

, whereas montmorillonite showed increments of 34% and 11% in

α

and

β

, respectively (Fig. 2). In contrast, XG has a minor effect on

s_{u}

in kerosene, which may be owing to the lack of XG hydration caused by the weak interaction between XG and kerosene (García-Ochoa et al. 2000; Hemar et al. 2001).

Data Reduction Based on the $s_{u} - LI$ Relationships

The

s_{u} - LI

relationships of the XG-treated kaolinite and montmorillonite in DI and 2-M-NaCl brine are presented in Fig. 3; the data for kerosene are not presented owing to the difficulties in obtaining the PL for the clay–kerosene mixtures (Kaya and Fang 2000). Both clays showed single

s_{u} - LI

relationships regardless of the presence of XG (Fig. 3). Therefore, the

s_{u}

of the XG-treated clays can be predicted using the LI assessed in the laboratory.

Fig. 3. Variation of $s_{u}$ with liquidity index for various clays in different pore fluids: (a) kaolinite in deionized water; (b) kaolinite in 2 M NaCl brine; (c) montmorillonite in deionized water; and (d) montmorillonite in 2 M NaCl brine.

The obtained

R

parameter for kaolinite in DI water [

R = 24.26

; Fig. 3(a)] is in accordance with a previous study, showing that

R

values of kaolinite range between 11 and 47 (Vardanega and Haigh 2014). However, the

R

value of montmorillonite in DI water [

R = 12.54

; Fig. 3(c)] is significantly lower than the value of 100 suggested by Wood (1990); particularly, it is close to the values of 15–20 reported previously by Vardanega and Haigh (2014). In brine, the

R

value of kaolinite [Fig. 3(c)] and montmorillonite [Fig. 3(d)] decreased to 13.44 and 7.69, respectively, indicating a reduction in soil activity (plasticity) due to salt-induced double-layer compression.

SEM Analysis of XG Behavior

Fig. 4 shows SEM images of the untreated (

m_{b} / m_{s} = 0 %

) and XG-treated (

m_{b} / m_{s} = 1 %

) clays. The presented SEM images were obtained after drying; thus, the drying process itself may have influenced the morphology of the observed clay specimens in Fig. 4. Rigid crystalline particles were observed for kaolinite [Figs. 4(a and b)], whereas montmorillonite exhibited undulated flexible sheets [Figs. 4(c and d)]. This morphological difference was owing to the strong hydrogen bonds formed between the kaolinite sheets (Żbik et al. 2010; Au and Leong 2016). The untreated kaolinite in DI water showed random face-to-face, edge-to-edge, and edge-to-face structures [Fig. 4(a)], whereas XG-induced face-to-face aggregates were observed for

m_{b} / m_{s} = 1 %

[Fig. 4(b)]. On the contrary, montmorillonite in DI water did not show distinctive structural variations following the XG treatment [Figs. 4(c and d)].

Fig. 4. SEM images of clay samples with different pore fluids and xanthan gum content: (a) untreated; and (b) 1% xanthan gum–treated kaolinite in deionized water; (c) untreated; and (d) 1% xanthan gum–treated montmorillonite in deionized water; (e) untreated; and (f) 1% xanthan gum–treated kaolinite in 2 M NaCl brine; (g) untreated; and (h) 1% xanthan gum–treated montmorillonite in 2 M NaCl brine.

Precipitated salt crystals, which may have existed as dissolved ions during the experimental processes, were observed on the surfaces of the clays in 2-M-NaCl brine [Figs. 4(e and g)]. Salt crystals were less frequently observed in the XG-treated kaolinite with 2-M-NaCl brine [Fig. 4(f)] than in untreated kaolinite [Fig. 4(e)]. Unlike the 1%-XG-treated montmorillonite in DI water [Fig. 4(d)], the XG-treated montmorillonite in 2-M-NaCl brine showed well-developed aggregates [Fig. 4(h)]. This morphological difference could help explaining the observed increase in

s_{u}

with

m_{b} / m_{s}

increase for both clays in 2-M-NaCl brine solutions.

Conclusion

In this study, we assessed the

s_{u}

of XG-treated clays upon considering the pore–fluid chemistry and clay mineral effect. Montmorillonite showed the highest

s_{u}

, which favors the formation of viscous double layers in DI water, followed by brine and kerosene. In contrast, kaolinite showed the highest

s_{u}

with kerosene, followed by DI water and brine, indicating the influence of interparticle attraction forces on the

s_{u}

of kaolinite clay.

The XG treatment altered the

s_{u}

of the clays in terms of pore–fluid viscosity variation and XG-induced clay-particle aggregation. In DI, XG showed the maximum undrained shear strength with 0.5%

m_{b} / m_{s}

; the dominant effect of XG changed from viscosity enhancement to particle aggregation. At

m_{b} / m_{s} = 0.5 %

, the shear parameters

α

and

β

of XG increased by approximately 50% and 70%, respectively. In contrast, the XG-induced particle aggregation decreased the

s_{u}

of montmorillonite clay gradually. The parameters

α

and

β

showed 16% and 11% decrements with 2% XG as compared to those of untreated montmorillonite, respectively. In 2-M-NaCl brine, XG increased the

s_{u}

of both clays owing to water absorption and interaction with the salt ions, thereby showing increments of 46% and 74% in

α

and

β

, respectively. In kerosene, which is nonpolar, XG did not affect the

s_{u}

of the two clays, indicating that hydrogel hydration is a prerequisite for XG treatment of clays. Kaolinite showed a higher

R

value than montmorillonite in DI. Moreover, both clays showed higher

R

values in DI than in brine. Meanwhile, the XG treatment had no effect on the

R

values.

Overall, the XG treatment was effective in increasing the shear strength of the clays in the undrained state, especially in high-salinity conditions. The optimal XG content and mineral properties must be considered to use XG in treating soils with low salinity (e.g., riverbeds). Nevertheless, to add XG to soils surrounded by low-permittivity pore fluids, such as in oil fields, XG gelation must be performed prior to soil treatment. In future studies, the water absorption capabilities of kaolinite, montmorillonite, and XG should be compared.

Notation

The following symbols are used in this paper:

$d$: penetration depth (mm);
$K$: cone factor;
LI: liquidity index, $(w - PL) / (LL - PL)$ ;
LL: liquid limit (%);
$m_{b} / m_{s}$: XG-to-soil mass ratio (%);
PL: plastic limit (%);
$R$: strength gain factor (ratio of undrained shear strength at PL and LL);
SSA: specific surface area ( $m^{2} / g$ );
$s_{u}$: undrained shear strength (kPa);
$s_{u}^{FC}$: undrained shear strength evaluated through fall cone test (kPa);
$s_{u}^{LL}$: undrained shear strength at LL (kPa);
$s_{u}^{PL}$: undrained shear strength at PL (kPa);
$s_{u}^{V}$: undrained shear strength evaluated through laboratory vane shear test (kPa);
$W$: weight of cone (g);
$w$: water content (%);
$X G$: xanthan gum biopolymer;
$α$: water content when $s_{u} = 1 kPa$ (%); and
$β$: variation of $\log s_{u}$ with $\log w$ .

Data Availability Statement

All data, models, and code generated or used during the study are present in the published article.

Acknowledgments

This study was financially supported by the Water Management Research Program funded by the Ministry of Land, Infrastructure, and Transport (MOLIT) of the Korean Government (21AWMP-B114119-06) and the New Faculty Research Fund of Ajou University.

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Published In

Journal of Geotechnical and Geoenvironmental Engineering

Volume 147 • Issue 11 • November 2021

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This work is made available under the terms of the Creative Commons Attribution 4.0 International license, https://creativecommons.org/licenses/by/4.0/.

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Received: Mar 10, 2020

Accepted: Jun 25, 2021

Published online: Aug 27, 2021

Published in print: Nov 1, 2021

Discussion open until: Jan 27, 2022

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Ilhan Chang, Ph.D., A.M.ASCE https://orcid.org/0000-0001-8369-0606 [email protected]

Associate Professor, Dept. of Civil Systems Engineering, Ajou Univ., Suwon-si 16499, Republic of Korea. ORCID: https://orcid.org/0000-0001-8369-0606. Email: [email protected]

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Yeong-Man Kwon https://orcid.org/0000-0002-4719-1241 [email protected]

Graduate Student, Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea. ORCID: https://orcid.org/0000-0002-4719-1241. Email: [email protected]

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Gye-Chun Cho, Ph.D. [email protected]

Professor, Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 34141, Republic of Korea (corresponding author). Email: [email protected]

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Suhyuk Park, Jun-Hyeok Yum, Minhyeong Lee, Gye-Chun Cho, Sojeong Lee, Ilhan Chang, Bioinspired Biopolymer Hydrogel Application to Improve Installation Efficiency and Load Carrying Capacity of Piles, Geo-Congress 2024, 10.1061/9780784485330.028, (268-277), (2024).
Abstract
Minhyeong Lee, Ilhan Chang, Gye-Chun Cho, Advanced Biopolymer–Based Soil Strengthening Binder with Trivalent Chromium–Xanthan Gum Crosslinking for Wet Strength and Durability Enhancement, Journal of Materials in Civil Engineering, 10.1061/JMCEE7.MTENG-16123, 35, 10, (2023).
Abstract
Yeong-Man Kwon, Ilhan Chang, Gye-Chun Cho, Consolidation and swelling behavior of kaolinite clay containing xanthan gum biopolymer, Acta Geotechnica, 10.1007/s11440-023-01794-8, (2023).
Crossref
Hao Ni, Sheng-Qiang Shen, Xian-Lei Fu, Chang-Ming Wang, Yan-Jun Du, Assessment of membrane and diffusion behavior of soil-bentonite slurry trench wall backfill consisted of sand and Xanthan gum amended bentonite, Journal of Cleaner Production, 10.1016/j.jclepro.2022.132779, 365, (132779), (2022).
Crossref

Abstract

Introduction

Materials and Methods

Characteristics of the Clay Materials

Characteristics of Xanthan Gum

Preparation of the XG–Clay Mixture

Experimental Details and Testing Procedure

Correlations between su and Index Properties

Results and Analyses

Effect of Pore–Fluid Chemistry on the su−w Relationship

Effect of Clay Mineralogy on the su−w Relationship

Effect of XG on the su−w Relationship

Data Reduction Based on the su−LI Relationships

SEM Analysis of XG Behavior

Conclusion

Notation

Data Availability Statement

Acknowledgments

References

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Correlations between $s_{u}$ and Index Properties

Effect of Pore–Fluid Chemistry on the $s_{u} - w$ Relationship

Effect of Clay Mineralogy on the $s_{u} - w$ Relationship

Effect of XG on the $s_{u} - w$ Relationship

Data Reduction Based on the $s_{u} - LI$ Relationships