Modelling of debris flow-boulder-barrier interactions using the Coupled Eulerian Lagrangian method

Abstract

The impact load of boulders transported by debris flow is crucial in designing protective structures constructed along the potential flow paths. In this study, the Coupled Eulerian-Lagrangian (CEL) method is applied to establish a three-dimensional model for analysing debris flow, boulders, and barrier interactions in various scenarios, with an Australian rivulet serving as a case study. The proposed CEL method was verified by simulating the runout and impact behaviour based on experimental granular and debris flow tests. Subsequently, a comprehensive series of numerical simulations explores the impacts of transported boulders on a rigid tooth barrier, encompassing various boulder shapes and sizes. The results indicate a direct correlation between boulder size and impact force, while the influence of boulder shape on peak impact force is minimal. Nevertheless, boulder shape affects the arrival time, as noted with increased boulder size. Although boulder dimensions remain the primary factor affecting impact force, variations in the geometry are observed to influence the overall dynamics of debris flow-boulder interactions. This study proposes a procedure for assessing barrier impact forces through simulations combining debris flow and boulder transport with the CEL method. The research presents the effectiveness of the CEL method in estimating the impact force of media transported by debris flows in intricate 3D terrains. The findings contribute significantly to the existing measures for assessing the risk of debris flows.