Multiscale modeling of crushable granular media

Abstract

Grain crushing is a common phenomenon in many engineering applications involving granular materials. Understanding grain crushing mechanisms is important for accurately assessing the performance of crushable granular media in diverse fields. However, the role of intermediate principal stress on the shear behavior of crushable granular sand remains relatively unexplored due to limited experimental data and analytical tools. To address this gap, a multiscale computational approach is adopted, which couples the non-smooth contact dynamics (NSCD) method for modeling large-scale discrete granular systems with peridynamics (PD) to rigorously analyze single particle crushing process along with intertwined evolution of particle size and shape. The numerical study enables comprehensive quantification and analysis of the macro- and micro-scale material behaviors influenced by grain crushing, such as strength, deformability, particle size and shape evolution, particle-scale forces, and development of anisotropy. Furthermore, systematic simulations are performed to explore the critical state behavior of crushable granular sand, aiming to identify unique characteristics such as the critical state stress ratio, void ratio, breakage index, and shape descriptors, which are independent of stress path and initial conditions. The multiscale computational framework presented in this study is further extended to incorporate dynamic loading scenarios. Numerical simulations are conducted to investigate the direct shearing of composite fault gouge samples with varying grain crushability, to understand how the development of grain crushing and strength heterogeneity impacts the friction and stability of fault zones. The study uncovers the intimate correlation between the transition from aseismic creep to slow slip events and fast earthquakes with heterogeneity and crushability of fault gouges. Specifically, the concentrated contact network in strong layers promotes long-lasting intense slow slip events accompanied by significant volume changes. On the other hand, significant crushing events in weak layers facilitate the occurrence of fast earthquakes across the entire fault.

Date of Award	2023
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Jidong ZHAO (Supervisor)