Abstract

A vast number of experimental and numerical studies have been performed in the literature to understand the fracturing process in brittle rocks under uniaxial compression; several types of cracks including tensile, shear, and combined tensile-shear have also been observed at the tip of pre-existing flaws. In this study, numerical simulations of a single oriented flaw in brittle rock materials in uniaxial compression were carried out using the extended finite element method (XFEM) and the displacement discontinuity method (DDM). The code FROCK was used for DDM simulations and the ABAQUS commercial package was used for the XFEM simulations. FROCK uses stress-based criteria in which the crack initiation is a function of the local stress relative to the strength of the material. In XFEM analysis, the maximum principal stress (MAXPS) failure criterion, assuming crack initiation and propagation in the direction perpendicular to the maximum principal stress, was used. The results from numerical simulations and experimental studies were in good agreement when predicting wing (tensile) cracks at the tip of the flaw. The stress intensity factors obtained from FROCK and XFEM were close to the values obtained from the closed-form solutions. However, the numerical simulations only predicted tensile cracks and failed to predict the shear cracks.

1. INTRODUCTION

The understanding of brittle rock failure in uniaxial compression is an important issue in rock engineering and petroleum engineering due to its applications in earthquake physics, rockburst in mining, wellbore stability, hydraulic fracturing, geothermal reservoirs, among others [1]. Several studies have addressed the deformation and fracture characteristics of brittle rocks under uniaxial compression, identifying the following main stages in the failure process [2-5]: (1) crack closure occurring during the initial stages when pre-existing microcracks close; (2) linear elastic deformation behavior after microcracks close, (3) crack initiation and stable crack growth, (4) critical energy release, crack propagation, and unstable crack growth, and (5) failure and post-peak stage. Crack initiation and growth result in the non-linear deformation behavior of the rock mass; thus, it is critical to study the crack initiation and propagation processes in brittle rock under uniaxial compression.

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