Effects of crack inclination on shear failure of brittle geomaterials under compression
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ORIGINAL PAPER
Effects of crack inclination on shear failure of brittle geomaterials under compression Xiaozhao Li 1,2 & Chengzhi Qi 1 & Zhushan Shao 2 & Chen Xia 1 Received: 11 July 2017 / Accepted: 30 November 2017 # Saudi Society for Geosciences 2017
Abstract A micromechanics-based approach is proposed to predict the shear failure of brittle rocks under compression. Formulation of this approach is based on an improved wing microcrack model, the Mohr-Coulomb failure criterion, and a micro-macro damage model. The improved wing microcrack model considers the effects of crack inclination angle on mechanical behaviors of rocks. The micro-macro damage model describes the relation between crack growth and axial strain. Furthermore, comparing experimental and theoretical relations between crack initiation stress and confining pressure, model parameters (i.e., μ, a, β, and φ) hardly measured by test are solved. Effects of crack inclination angle, crack size, and friction coefficient on stress-strain relation, compressive strength, internal friction angle, cohesion, shear failure plane angle, and shear strength are discussed in details. A most disadvantaged crack angle is found, which is corresponding to the smallest compressive strength, cohesion, internal friction angle, and shear strength of rocks. Rationality of the theoretical results is verified by the published experimental results. This approach provides a theoretical prediction for effects of microcrack geometry on macroscopic shear properties in brittle rocks under compression. Keywords Micromechanics . Shear properties . Crack inclination angle . Strength . Damage
Introduction Natural rocks intrinsically exist numerous microcracks. Microcrack growth has an important influence on the mechanical behaviors of brittle rocks. The compressive-shear fracture is an important failure form of brittle rocks under the lithospheric conditions. Thus, the study of shear failure caused by crack growth in brittle rocks under compression has an important meaning for evaluating the stability of earth crust or the safety of underground engineering (Martin and Chandler 1994; Chang and Lee 2004; Heap et al. 2009; Shen et al. 2014).
* Chengzhi Qi [email protected] 1
Beijing Research Center of Engineering Structures and New Materials, Beijing University of Civil Engineering and Architecture, Beijing 100044, China
2
School of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
Process of microcrack growth in brittle rocks was measured and observed by the different experimental methods. Based on acoustic emission (AE) monitoring, the compression-induced crack growth was characterized by several distinct stages, i.e., crack initiation, stable crack propagation, unstable crack propagation, and crack coalescence (Martin and Chandler 1994; Chang and Lee 2004). Furthermore, through scanning electron microscopy (SEM), the phenomena of crack initiation, crack propagation, and coalescence were also observed directly in brittle rocks (Fonseka et al.
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