The Monotonic and Cyclic Shear Behaviour of Low Plasticity Soil Treated with Biopolymer

Soil improvement using biopolymers has gained increasing attention in recent years. Despite considerable effort, the response of biopolymer-treated soil to monotonic and cyclic loads is still not understood very well, which is why this current study carried out a series of monotonic and cyclic triaxial shear tests on a low plasticity soil treated by Xanthan Gum (XG) biopolymer. While different confining pressures are set in monotonic tests, various combinations of cyclic stress ratios and loading frequencies are also used in cyclic tests considering the work condition of subgrade soil under railways. The results show that biopolymer significantly hardens soil and raises its dilative tendency due to coupled effect of thickened pore fluid and promoted interparticle cohesion, depending on the degree of confinement and XG content. As XG content increases, the slope of the critical state line becomes steeper with stronger cohesion intercept and tensile strength. Biopolymer increases the resistance of soil to cyclic loading by promoting soil dilatancy and decreasing the cumulative excess pore water pressure, thus reduced settlement. This study utilises a novel in-house synchrotron-FTIR microspectroscopy imaging technique to assess the chemical distribution of biopolymer-treated soil and provide valuable insight into the molecular interactions at the biopolymer-soil interface