MPM modelling of debris flow entrainment and interaction with an upstream flexible barrier

Abstract

Flexible barriers may be installed upstream in debris flow channels to reduce entrainment of bed material. Simulating both the entrainment and the impact on a barrier by the same numerical tool remains challenging. For this purpose, a three-dimensional one-phase material point method (MPM) software is used herein to back-calculate two large-scale flume experiments. These experiments were conducted to measure the entrainment of an erodible bed and the impact on a flexible barrier. To simulate the entrainment of the wet bed, a Mohr–Coulomb softening model is introduced. In the model, the apparent friction angle of the bed material decreases as a function of the distortional strain, effectively reproducing the pore pressure increase observed in the experiments. From the tests and the numerical simulations, we identify two main mechanisms leading to entrainment: (i) the direct rubbing and colliding effect of the flow on to the bed and (ii) a significant bed shear strength reduction. Concerning the first mechanism, existing models only consider the rubbing of the bed surface by a shear stress parallel to the slope. However, we observe that a ploughing-type erosion occurs due to normal stresses acting on the bed in the flow direction. The additional ploughing explains why beds which are mechanically stronger than the flow can also be partly entrained. Larger entrainment volumes are found when the bed material loses shear strength due to pore pressure buildup that eventually leads to a self-propelled entrainment where the bed no longer has frictional strength to carry its own weight.

Numerical modelling of an alpine debris flow by considering bed entrainment

“…In the last decades, many different numerical models for the simulation of debris flows and flow-like landslides have been developed. Due to the simpler governing equations and less computational time compared with the fully 3D numerical models, such as the 3D models based on smoothed particle hydrodynamics (SPH) (Wang et al, 2016;Dai et al, 2017), material point method (MPM) (Li et al, 2020;Vicari et al, 2022) and particle finite element method (PFEM) (Zhang et al, 2020;Wang and Zhang, 2022), depth-averaged models derived from the principles of continuum mechanics have been widely applied to reproduce and analyze the dynamic processes of flow-like landslides. The unsteady debris flow model for simulating erosion/deposition process of sediment during the flow was proposed (Chen, 1987).…”

A Depth-Averaged Material Point Method for Shallow Landslides: Applications to Snow Slab Avalanche Release

“…MPM is a Eulerian-Lagrangian particle-based method initially developed by Sulsky et al (1994). Due to its ability to handle processes including large deformations, fractures and collisions, this elegant hybrid method found great interest over the last two decades, both in geomechanics, e.g., for the modeling of fluid-structure interaction (York II et al, 2000), porous media micromechanics (Blatny et al, 2021(Blatny et al, , 2022, granular flows (Dunatunga & Kamrin, 2015), snow avalanche release (Gaume et al, 2019;Trottet et al, 2022), snow avalanche dynamics (Li et al, 2021), glacier calving (Wolper et al, 2021), debris flows (Vicari et al, 2022), landslides (Soga et al, 2016 and rockslides (Cicoira et al, 2022), as well as in computer graphics (Stomakhin et al, 2013;Jiang et al, 2016;Schreck & Wojtan, 2020;Daviet & Bertails-Descoubes, 2016). After its first application to snow slab avalanches, Gaume et al (2019) analysed crack propagation and slab fracture patterns and reported crack speeds above 100 m/s on steep terrain.…”

Bi‐Linear Laws Govern the Impacts of Debris Flows, Debris Avalanches, and Rock Avalanches on Flexible Barrier

“…Besides physical experiments and theoretical analysis, many numerical methods have been applied to investigate the impacts of geophysical flows on flexible barriers, such as mesh‐free methods (smoothed particle hydrodynamics [SPH], Fávero Neto et al., 2020; Material Point Method, Vicari et al., 2022; discrete element method [DEM], Albaba et al., 2017), grid‐dependent methods (finite element method [FEM], Brighenti et al., 2013), and coupled frameworks (SPH‐DEM‐FEM, B. Li, Wang, et al., 2021; DEM‐FEM, Liu et al., 2020; computational fluid dynamics [CFD] coupled with DEM, Kong, Li, et al., 2021; Lattice Boltzmann Method coupled with DEM and FEM, Leonardi et al., 2016; CFD‐FEM, Von Boetticher et al., 2011). Nonetheless, simplifications of flow dynamics and flexible barriers have prevented a deeper understanding of the underlying relations and mechanisms of the flow‐barrier interactions.…”

“…On the one hand, the solid‐fluid nature of a geophysical flow plays a crucial role in predicting its propagation and impact (De Haas et al., 2021; Iverson, 1997; Pudasaini & Mergili, 2019) but has commonly been modeled as pure continuum or granular flows (Albaba et al., 2017; Liu et al., 2020; Von Boetticher et al., 2011). On the other hand, permeable flexible barrier systems (Figure 1a) are simulated as membranes (Leonardi et al., 2016; Vicari et al., 2022), and net units are generated in a 2D plane (Brighenti et al., 2013; Kong, Li, et al., 2021; B. Li, Wang, et al., 2021) by ignoring the cable‐ring‐ring slidings in a 3D space. However, these omitted in‐flow multiphase and in‐barrier multiway interactions are essential for accurately predicting systematic structure deformations, evolving load sharings and distributions, and thus peak barrier load.…”