Impact-induced collapse of an inclined wet granular layer

TL;DR

This study investigates how impacts can trigger the collapse of inclined wet granular layers, combining experiments and simulations to identify conditions leading to terrain failure relevant to landslides and asteroid surface dynamics.

Contribution

It introduces a combined experimental and numerical approach to determine collapse conditions in wet granular layers caused by impacts, including a simple block model for prediction.

Findings

Collapse occurs near maximum stable angle with strong impact vibrations.

Impact-induced acceleration attenuates anisotropically in space.

The block model effectively predicts collapse conditions.

Abstract

The collapse of an inclined cohesive granular layer triggered by a certain perturbation can be a model for not only landslides on Earth but also relaxations of asteroidal surface terrains. To understand such terrain dynamics, we conduct a series of experiments of a solid-projectile impact onto an inclined wet granular layer with various water contents and inclination angles. As a result, we find two types of outcomes: "crater formation" and "collapse". The "collapse" phase is observed when the inclination angle is close to the maximum stable angle and the impact-induced vibration at the bottom of wet granular layer is sufficiently strong. To explain the collapse condition, we propose a simple block model considering the maximum stable angle, inclination angle, and impact-induced vibrational acceleration. Additionally, the attenuating propagation of the impact-induced vibrational acceleration is estimated on the basis of three-dimensional numerical simulations with discrete element method using dry particles. By combining wet-granular experiments and dry-granular simulations, we find that the impact-induced acceleration attenuates anisotropically in space. With a help of this attenuation form, the physical conditions to induce the collapse can be estimated using the block model.