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

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.

Xanthan biopolymer-based soil treatment effect on kaolinite clay fabric and structure using XRD analysis

“…Additionally, the MDD decreases as XG changes from 1.31 g/cm 3 (untreated kaolinite) to 1.22 g/cm 3 ( m b / m s = 2.0%). These results match the previous findings that XG with m b / m s = 0.5% exhibit the local maximum liquid limits 11 , 52 and s u 10 .…”

“…The biopolymer-based soil treatment (BPST), which uses exo-cultured biopolymers resulting from the metabolism of living organisms for soil improvement, has been extensively studied for integration as an environmentally friendly soil improvement technique 7 – 9 . The biopolymers affect soil grains by increasing the pore-fluid viscosity and particle interaction 10 . Based on the interaction of biopolymers and soils, biopolymers have shown their ability to enhance soil consistency 11 , coagulation 12 , soil strength 13 – 18 , surface erosion 19 – 22 , and hydraulic conductivity control 23 – 26 .…”

“…In the context of clays, the presence of biopolymers can lead to direct ionic bonding with the surface of clay particles 27 , resulting in modifications of the clay fabric, and geometric arrangement of the soil particles 10 , 11 . For instance, Mahamaya et al 28 investigated the effect of xanthan gum (XG), guar gum, and cellulose biopolymers on fly ash and mine tailings.…”

“…3 c). This tendency can be attributed to the formation of an interconnecting network—that is, hydrogen bonding or direct electrical bonding—between the kaolinite particles 10 , 57 , resulting in a modification of the kaolinite fabrics as indicated by the XRD results, which resist the compaction energy 16 , 56 . Ni et al 58 also investigated the increase in OMC and the decrease in MDD with XG, indicating that this alteration is caused by the clay content and biopolymer characteristics.…”