3D numerical modelling of bouldery debris flows and their interaction with mitigation structures

Abstract

Debris flow is a flow-type landslide on channelized natural terrain which may cause great destructions. Large boulder entrainment during the transport of debris flow often changes rheological property of debris flow and causes extra impact load on barriers. Current practice has long neglected the interaction between boulders, debris flow, and resisting structures such as baffles and slit dams, resulting in over conservative design of such mitigation measures. In this study, two numerical approaches based on 1) fully resolved SPH-DEM coupling and 2) two-level DEM are developed to simulate bouldery debris flow. To accurately capture the microscopic interactions between boulders and debris flow, the numerical approaches are further implemented with GPU-based parallel computing to achieve high-resolution results for both the fluid and particulate systems at reasonable computing time. The resolved SPH-DEM is first benchmarked and a relative resolution for SPH particle is further proposed to accurately predict boulder-fluid interaction. The model is then used to study the impact mechanism of bouldery debris flow on baffles. The results show that the viscosity of slurry influences the formation of bouldery front. When the bouldery front exists, the peak discharge could increase to 1.5 - 1.8 times of that without boulders. The coupled SPH-DEM is further used to model debris flow on a natural terrain, and the GPU-based simulation shows its capability to model complex topology efficiently. The simulation results show that boulder entrainment on natural channel may potentially reduce the mobility of debris flow. It is noted that practical use of resolved SPH-DEM for debris flow predictions still needs rigorous calibration of the debris rheology. Numerical results by the two-level DEM reveals that when dense granular flow impacts on a slit dam, the slit width to particle diameter ratio (s/d) has a significant effect on the peak discharge, while the pile-up height remains unchanged. Boulder entrainment is found to potentially reduce the discharge by temporary clogging at the slit dam, but the reduction effect depends on boulder concentration and is highly fluctuating. Permanent clogging will not occur if the boulder concentration is low.

Date of Award	2022
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Jidong ZHAO (Supervisor)