Experimental Investigation and Numerical Simulation on the Crack Initiation and Propagation of Rock With Pre-Existing Cracks

Xun Xi,Qifeng Guo,Xu Wu,Meifeng Cai

doi:10.1109/access.2020.3009230

Abstract

Rock mass behavior is determined not only by the properties of the rock matrix but also mostly by the pre-existing cracks in the rock mass. Before the overall failure of rock, the crack initiation and propagation around the tip of pre-existing cracks (i.e., pre-crack) will occur and contribute to rock failure. In this paper, the deep granite from a gold mine is taken and made to specimens with the pre-crack of 0.3 mm thickness. Uniaxial compression tests are carried out on the pre-cracked specimens. The acoustic emission (AE) sensors and digital image correlation (DIC) system are employed to record the failure characteristics of the specimens. The extended finite element method (XFEM) with the non-local stress field calculation is used to simulate the crack initiation and propagation of pre-cracks. The crack patterns, opening and shearing displacements of the cracked surface, and the crack length development are obtained from numerical simulations. Finally, the effects of friction of crack surface on the crack pattern and crack propagation are investigated and discussed. It has been found that, for pre-cracked specimens, crack initiation and propagation will occur when the stress is much smaller than the rock compressive strength. And in the range of pre-crack angle 30-60°, the larger the pre-crack angle is, the larger the compressive strength is. The crack patterns from numerical simulations have a good agreement with those from experimented DIC results. Moreover, the order of crack propagation speed is consistent with the order of the compressive strength. The crack pattern and crack propagation are affected by the friction coefficient of the cracked surface.

Highlights

Natural joints or fractures widely existed in rock significantly affect rock mechanical response under various loading condition, which can even cause serious engineering disasters
For pre-cracked specimens, crack initiation and propagation will occur one or more times when the stress is much smaller than the rock compressive strength
acoustic emission (AE) events and surface strain were recorded by the AE monitoring system and the digital image correlation (DIC) technique

Summary

Introduction

Natural joints or fractures widely existed in rock significantly affect rock mechanical response under various loading condition, which can even cause serious engineering disasters (e.g., the roof falling, rock burst and landslides). Natural fractures usually occur in sets that are more or less parallel and regularly spaced and the oriented fractures decrease the strength and stiffness of the rock [1]–[5]. It is attractive for physically understanding the mechanical behavior of rock with various pre-existing cracks (i.e., pre-cracks) [6]–[8]. Yang et al [11]–[13] carried out a series of uniaxial and triaxial compression tests of pre-cracked sandstone specimens. Lee and Jeon [8] carried out uniaxial compression tests on granite specimens with pre-cracks of 1 mm thickness and found that the failure of specimens were

Methods

Results

Conclusion