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Geomechanics and Engineering
  Volume 14, Number 2, February10 2018 , pages 195-202
DOI: https://doi.org/10.12989/gae.2018.14.2.195
 


Experimental study on propagation behavior of three-dimensional cracks influenced by intermediate principal stress
Xi Z. Sun, B. Shen and Bao L. Zhang

 
Abstract
    Many laboratory experiments on crack propagation under uniaxial loading and biaxial loading have been conducted in the past using transparent materials such as resin, polymethyl methacrylate (PMMA), etc. However, propagation behaviors of three-dimensional (3D) cracks in rock or rock-like materials under tri-axial loading are often considerably different. In this study, a series of true tri-axial loading tests on the rock-like material with two semi-ellipse pre-existing cracks were performed in laboratory to investigate the acoustic emission (AE) characteristics and propagation characteristics of 3D crack groups influenced by intermediate principal stress. Compared with previous experiments under uniaxial loading and biaxial loading, the tests under true tri-axial loading showed that shear cracks, anti-wing cracks and secondary cracks were the main failure mechanisms, and the initiation and propagation of tensile cracks were limited. Shear cracks propagated in the direction parallel to pre-existing crack plane. With the increase of intermediate principal stress, the critical stress of crack initiation increased gradually, and secondary shear cracks may no longer coalesce in the rock bridge. Crack aperture decreased with the increase of intermediate principal stress, and the failure is dominated by shear fracturing. There are two stages of fracture development: stable propagation stage and unstable failure stage. The AE events occurred in a zone parallel to pre-existing crack plane, and the AE zone increased gradually with the increase of intermediate principal stress, eventually forming obvious shear rupture planes. This shows that shear cracks initiated and propagated in the pre-existing crack direction, forming a shear rupture plane inside the specimens. The paths of fracturing inside the specimens were observed using the Computerized Tomography (CT) scanning and reconstruction.
 
Key Words
    three-dimensional crack; true tri-axial loading; intermediate principal stress; propagation; acoustic emission; CT scan and reconstruction
 
Address
Xi Z. Sun: College of Mining and Safety Engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Huangdao District, Qingdao, Shandong Province, 266590, China

B. Shen: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Huangdao District, Qingdao, Shandong Province, 266590, China

2.) Commonwealth Scientific and Industrial Research Organization (CSIRO) Energy, P.O. Box 883, Kenmore, Brisbane QLD 4069, Australia

Bao L. Zhang: 1.) College of Mining and Safety Engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Huangdao District, Qingdao, Shandong Province, 266590, China

2.) School of Architecture and Civil Engineering, Liaocheng University, NO.1 Hunan Road, Dongchangfu District, Liaocheng, Shandong Province, 252059, China



 

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