Velocity and Temperature Profile Evolution in Dense Granular Flows

Dense granular flows are pivotal in a range of geological hazards, such as landslides, fault slip zones, debris flows, and rock avalanches. However, the coupled thermo-mechanical characteristics that dominate their evolutionary processes remain inadequately clarified. In this research, ring shear tests were carried out under high normal stress conditions using nearly crush-resistant glass beads, aiming to explore the variations of velocity and temperature distributions during the shearing process. High-speed imaging combined with particle image velocimetry (PIV) was utilized to resolve the granular velocity field, while both infrared thermography and embedded thermocouples were employed to capture thermal signals across the shear zone. A distinct temporal discrepancy between mechanical and thermal responses was observed: in the shear initiation phase, particle velocities rose sharply, whereas the temperature remained almost constant. On the contrary, during the steady-state phase, the velocity profiles stabilized, while temperature continued to accumulate—particularly within the lower shear band. Furthermore, slow thermal evolution was detected in the upper quasi-static region, and the local heating at the thermocouple interfaces exceeded the infrared surface measurement results. These findings emphasize the cumulative and spatially heterogeneous features of frictional heat generation in dense granular flows, providing valuable references for the validation of thermo-mechanical models associated with dense granular flows. This study carries important implications for deciphering the physical mechanisms that govern the evolution of velocity and temperature in geological hazard-related flows.