Effect of biotreatment on geotechnical behaviour of clayey sand with various fines contents

Clayey sand is a geological material composed of sands and fines. For clayey sand, fines content (FC) significantly affects the soil structure and in turn the mechanical behaviours. Hitherto, the reinforcing effect of biopolymers in treating clayey sand with various FCs is largely unexplored. This study aims to fill this gap by conducting a series of geotechnical tests on the xanthan gum (XG)–treated kaolinite clay–sand mixtures having FCs within 50%. Results indicated that hydrophilic XG increased soil consistency, exhibiting a decreasing efficiency with the increasing FC. The compaction and shear behaviours of the XG-treated clayey sand containing FC ≤ 30% and FC ≥ 40% were different. A schematic model assisted by scanning electron microscope microstructure images was proposed to describe the soil structure alteration from sand-dominated skeleton to the one composed of both sand skeleton and XG–clay matrix, as the cause of the observed FC-dependent soil physical and mechanical behaviours. In the current research, XG treatment has been evidenced effective in improving the shear strength of clayey sand by way of increased soil cohesion and friction angle, and thus is suggested to be applied for reinforcing clayey sand in sustainable geotechnical engineering practices.