Abstract
This study investigates the influence of guar gum (G), xanthan gum (X), and their cross-linked blend on the shear strength and consolidation characteristics of soils with contrasting plasticity and mineralogical characteristics. Direct shear, one-dimensional consolidation, constant head permeability tests, SEM and XRD analyses were conducted on high-plastic clay, medium-plastic clay, and sand-dominant soil treated with standalone (2G, 2X) and combined (1G+1X) biopolymer dosages under curing periods up to 28 days. The cross-linked treatment produced the most consistent overall improvement. In the high-plasticity soil, cohesion increased from 56.87 to 81.39 kPa and the friction angle increased from 7.8° to 10.5°. In the medium-plasticity soil, cohesion increased to 77.47 kPa and the friction angle reached 12.2°. In the sand dominant soil, the friction angle increased from 39.1° to 42.9°, while cohesion increased from 12.74 to 23.53 kPa. At 800 kPa, the cross-linked blend reduced the void ratio to 0.18 and 0.14 in the high- and medium-plasticity soils, respectively. Hydraulic conductivity decreased to 8.45 × 10⁻⁹, 8.21 × 10⁻⁹, and 9.10 × 10⁻5 cm/s in the three soils. These improvements are attributed to polymer bridging, hydrogen bonding, pore filling, hydrogel formation, and mineralogy-dependent soil-polymer interactions. The findings demonstrate the potential of cross-linked biopolymers as sustainable stabilizers for geotechnical applications.