Influence of basel stress fluctuations on the friction behavior of rock-ice granular flows: Insights from flume experiments

Rock-ice granular flows in high-altitude cold regions exhibit extreme mobility and destructive potential, posing severe threats to lives and infrastructure. Basal stress, governing the interaction between the flow and the underlying substrate, is critical for understanding their high mobility and erosion behavior. However, systematic investigations into basal stress fluctuations and their relationship with frictional behavior in rock-ice granular flows remain scarce, particularly regarding the effects of ice content and inclination angle. In this study, a series of flume experiments were conducted with ice contents ranging from 0% to 100% and flume inclination angles of 30°–45°. A triaxial force sensor and high-speed imaging with particle image velocimetry (PIV) were employed to measure basal normal and shear stresses, flow depth, and velocity. The results reveal that both normal and shear basal stresses initially increase slightly at 10% ice content but then decrease progressively as ice content increases further, while both stresses increase monotonically with inclination angle. These variations are attributed to the combined effects of hydrostatic pressure (overburden load and flow depth) and dynamic pressure (particle collisions and flow velocity). Dimensionless normal impulse decreases with ice content, whereas dimensionless tangential impulse increases, indicating enhanced normal interactions but weakened tangential interactions at higher ice concentrations. The maximum stress and standard deviation of stress both scale linearly with the time-mean stress, confirming that stress fluctuations are governed by bulk flow conditions (density, overburden load). The effective friction coefficient μ shows a linear decrease with increasing ice content and a negative correlation with the Froude number Fr. Additionally, the normalized standard deviation of normal stress correlates positively with μ, while that of shear stress correlates negatively, suggesting that normal stress fluctuations from particle-substrate collisions enhance basal friction, whereas tangential fluctuations reduce it. These findings provide quantitative insights into the basal stress dynamics of rock-ice granular flows and establish a basis for improved hazard assessment and mitigation strategies in high-altitude mountain regions.