Modification of dispersive soil using xanthan gum and water glass: dispersivity, mechanical properties and mechanisms

Dispersive soil has strong dispersibility and low erosion resistance in water. Biological and chemical modification offers an environmentally friendly soil improvement method. This study investigates the effects of biopolymer xanthan gum (XG) and water glass (WG) on the and properties of dispersive soil. Specimens containing 5% WG with varying XG content (0.1–0.5% for dispersivity assessment; 1–5% for mechanical testing) were prepared and cured for 28 days. Dispersivity and water stability were evaluated through pinhole tests, cube sample crumb tests, and remoulded sphere sample crumb tests. Mechanical properties were assessed via Brazilian tensile strength, unconfined compressive strength, and direct shear strength tests. Chemical (pH), mineral and microstructural changes were systematically analyzed. Additionally, modification mechanisms of different modification materials for dispersive soils were compared. The long-term strength was predicted using the Generalized GM(1,1) power model and Particle Swarm Optimization algorithm. Results show that when the XG content reaches 0.4% and 0.5%, the soil can transform from strong dispersibility to non-dispersibility. WG and XG can significantly improve the mechanical properties. When the XG content is 5%, BTS is increased by 288%, while the internal friction angle shows a trend of first slightly increasing and then decreasing. There is a significant negative correlation between pH and mechanical strength, with a 12.6% decrease at 5% XG content. Prediction results and mechanism comparison confirm that XG + WG is a long-efficiency and low-impact biochemical composite modifier. This study provides an efficient solution to address a series of disaster issues caused by dispersive soil.