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.
Highlights
Undrained shear strength is an important geotechnical engineering design parameter for clayey soils in undrained conditions, which is generally assessed by high shear rates and poor drainage conditions (Gutierrez et al 2008; Kayabali and Tufenkci 2010)
We explored the effect of the xanthan gum (XG) content, clay mineralogy, and pore–fluid type on the su of kaolinite and montmorillonite clays
This study investigated the differences in clay behaviors between water-based (DI water and 2-M-NaCl brine) and kerosene-based mixtures
Summary
Undrained shear strength (su) 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). 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 su of clays; the edge-to-face associations show higher su 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). The su 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)
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