49 / 2021-11-14 23:17:04

Ambient air pressure and pore gas pressure during the propagation of dry granular flows along a slope: An experimental viewpoint

rock avalanches; ambient air pressure; pore gas pressure; kinetics feature; shear erosion mechanism

A rock avalanche indicates a certain state of motion after a high degree of fragmentation during the propagation of landslides, and the participation of a large amount of ambient air may change the dynamic characteristics. We report the ambient air pressure and bottom pore gas pressure during the dry granular flow propagation phase in a laboratory chute experiment, aiming to study the possible interaction mechanism between gas and particles. We find that the edge area may be subjected to two air impacts: the first impact originates from the front ambient airflow, which reaches twice the particle velocity, and the second impact entails the upper ambient air driven by high-speed friction between the granular flow surface interface and ambient air. Our experiment reveals that the pore gas pressure at the bottom does not notably support solid particles (less than 6% and lower away from the release zone), and the main features include (1) a relatively short underpressure period at the head of the sliding body, which may be the result of the propagation of the front ambient airflow; and (2) a relatively overpressure stage widely present at the bottom of the sliding body, which may be the result of air entrapment. Changes in underpressure and overpressure may produce a shear erosion mechanism enabling gravity flows to transport loose debris on the substrate and facilitating volume increase, and the interaction between gas and solid particles may be more notable in geophysical flows, thus intensifying this entrainment effect.