Effects of dehydration on the residual shear strength of hydrous material in high-velocity shearing

Abstract

The residual shear strength of materials on the shear surface is a crucial parameter in controlling the landslide movement and could be influenced by the sliding velocity. Recent studies suggested that dehydration of hydrous materials due to friction heating during high-velocity shearing and under high normal stress may weaken shear strength. However, the underlying mechanisms remain unclear. To investigate this, a series of ring shear tests on halloysite nanoparticles (ADH) were conducted in both their original (ADH_orig) and pre-dried at 500 °C (ADH₅₀₀) states, under normal stress of 200 kPa and varying shear velocities. Results show the residual shear strengths (τ_r) increase slightly with shear velocity (V) at low velocities (0.1–10 cm/s), but decrease at higher velocities, with a sharp around 210 cm/s, and with τ_r for ADH_orig being half of that of ADH₅₀₀. Estimating the increasing temperature of the shear surface and X-ray diffraction (XRD) analysis on the post-test samples around the shear zone confirmed sample dehydration during shearing. Moreover, the dehydration of the sample during high-velocity shearing can result in the release of water vapor due to flash heating. It is inferred that the vapor may elevate the pressure along the sliding surface, consequently reducing the shear strength. These findings provide valuable insights into the role of sample dehydration in shear strength reduction, enhancing the understanding of landslide dynamics.