Fracture Initiation and Propagation in a Brazilian Disc with a Plane Interface: a Numerical Study
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ORIGINAL PAPER
Fracture Initiation and Propagation in a Brazilian Disc with a Plane Interface: a Numerical Study M. Cai
Received: 28 April 2012 / Accepted: 27 October 2012 / Published online: 15 November 2012 Ó Springer-Verlag Wien 2012
Abstract In the present study, fracture initiation and propagation from a pre-existing plane interface in a Brazilian disc is investigated using a finite-discrete element combined method. Different fracture patterns, depending on the frictional resistance of the pre-existing crack or interface, are observed from the numerical simulation. It is found that when there is no or very little frictional resistance on the surfaces of the pre-existing crack, the primary fractures (wing cracks), which are tensile in nature and are at roughly right angles to the pre-existing crack, start from the tips of the pre-existing crack. As the friction coefficient increases, the wing cracks’ initiation locations deviate from the crack tips and move toward the disc center. Secondary fractures, which are also tensile in nature, initiate from the disc boundary and occur only when the length of the preexisting crack is sufficiently long. The secondary fractures are roughly sub-parallel to the pre-existing crack. The failure load is found to be influenced by the friction coefficient of the pre-existing crack. A 38 % failure load increase can result when the friction coefficient changes from 0 to 1. A good understanding of the fracture initiation and propagation in the forms of primary and secondary fractures provides insight into explaining some fracture patterns observed underground. Keywords Fracture initiation Fracture propagation Brazilian test FEM/DEM combined method Shear fracture Tensile fracture
M. Cai (&) Bharti School of Engineering, Laurentian University, Sudbury, ON, Canada e-mail: [email protected]
1 Introduction Rocks usually contain grains and randomly or non-randomly oriented flaws in the form of microcracks. Fractures start to initiate and propagate when the stress is over a certain threshold. The rock fracturing process is complex. Figure 1 presents one example of fracture patterns observed in a South African mine. The main shear rupture was formed due to a rockburst event. In addition to the shear rupture, some tensile fractures, which were dominantly on the lower side of the shear fracture, were generated as well. Observation of fracture patterns like this emphasizes the need to understand the mechanism that governs the failure of rock mass in the vicinity of underground excavations. Fracture process modeling has been a subject of considerable research interests and many researchers employ experimental, analytical, and numerical techniques ranging from finite difference (FDM), finite element (FEM) and boundary element (BEM) based models to, recently, finitediscrete element combined (FEM/DEM) approach to study the progressive failure of engineering materials (Cottrell et al. 2003; Cai and Kaiser 2004; Pine et al. 2006; Cai 2008). A Brazilian test with a pre-existing inclined
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