Friction-induced heating and softening of shear band soil in high-velocity rotary shear tests for assessing landslide risk

Upon the initiation of catastrophic high-speed landslides, the friction coefficient on the slip surface often decreases sharply, in some cases approaching a nearly frictionless state. Various hypotheses have been proposed to explain this phenomenon, including the thermal pressurization-induced weakening mechanism. To investigate the frictional heating and softening behavior of shear band soils under high-velocity shearing conditions, this study conducted high-velocity friction tests on synthetic shear band soil using a rotary shear apparatus. The experiments were performed under varying conditions of water content, normal stress, and shear rate. The results indicate that, the lower the water content, the more pronounced the frictional heating, with the highest temperature reaching 172 °C under dry conditions; when the water content reaches 15%, the maximum temperature does not exceed 60 °C. The softening of the friction coefficient is most significantly influenced by the water content. Both the peak and residual friction coefficients decrease with increasing water content. Under a constant shear rate of 1 m/s and a normal stress of 1.6 MPa, the residual friction coefficient decreased to 0.05 when the water content increased to 15%. Under variable shear rate conditions, when the shear rate increased to 2 m/s, the residual friction coefficient stabilized at approximately 0.06. In the present tests, no direct relationship has been observed between the softening of the friction coefficient and the process of frictional heating. The frictional liquefaction under conditions of high water content and high shear rate is likely the main cause of the sharp reduction in residual friction coefficients observed in these tests. The results of this study further enrich the understanding of the mechanisms of frictional heating and weakening in shear band soils, and provide fundamental experimental data for investigating the high-velocity sliding mechanisms of catastrophic landslides.