Abstract

In the present research, numerical simulations of dynamic tests conducted in split Hopkinson pressure bar on Rewa shale are performed using discrete element method. Voronoi based polygons are used to represent the rock grains. Rewa shale is a transversely isotropic rock and is collected from the Rewa region in the Madhya Pradesh state of India. The rock is loaded at strain rate of ~200/s. The dynamic compressive properties are assessed at three anisotropy angles viz. 0°, 45°, and 90°. The initiation, propagation, and coalescence of cracks during dynamic failure is evaluated. It is found that the failure of specimens is mainly shear under dynamic loading. In the post-peak phase, many tension cracks are also observed. For samples with 45° angles, cracks initiate along the bedding planes first. For samples with anisotropy angle 0° and 90°, cracks begin in the internal rock matrix.

Introduction

Most rocks in nature are anisotropic. The anisotropy is due to the presence of laminations, bedding planes, foliations, and layering. Due to anisotropy, mechanical properties like strength and deformation vary with direction. A special class of anisotropy is transverse isotropy. In transversely isotropic rocks, mechanical properties remain same in the parallel bedding planes, while they vary in the direction perpendicular to these planes. It is important to take anisotropy into account for measuring stresses and displacements for designing civil and rock engineering structures (Wang et al., 2003).

In addition to static loads, rocks are subjected to dynamic loads such as that during earthquakes, tunneling operations or an explosion. The dynamic mechanical behavior of rocks has been investigated by many researchers (Dai et al., 2013; Kang et al., 2016; Shi et al., 2018; Xu et al., 2020; X. Zhang et al., 2018; R. Wu et al., 2020). Split Hopkinson pressure bar (SHPB) has been commonly used to test rocks at high strain rates. (X. Zhang et al., 2018) tested slate up to ~150/s in SHPB. It was found that the anisotropy first decreases and then increases as the loading rates increase. (R. Wu et al., 2020) evaluated anisotropic behavior of phyllite till ~150/s. U-type anisotropy was reported in both the studies. In the latter study, samples with β ≥ 67.5° were found to have higher strain rate dependency. The angle β is defined as the angle between the direction of major principal stress and the bedding planes.

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