Numerical analyses of mesh size effects on core discing
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ORIGINAL PAPER
Numerical analyses of mesh size effects on core discing Songqing Lin 1 & Chuanqing Zhang 1,2 & Hui Zhou 1,2 & Feng Dai 3 Received: 18 October 2016 / Accepted: 30 April 2020 # Saudi Society for Geosciences 2020
Abstract Although the nonlinear numerical methods to study core discing mechanisms have their merits in terms of linear elastic models, the effects of mechanical parameters and mesh size in numerical simulations still have limits on the accuracy of the results. To address this problem, a parametric sensitivity analysis was conducted to understand the influence of shear and tensile mechanical parameters and mesh size on the numerical results of core discing. Numerical results show that the shear and tensile mechanical parameters have a “cliff effect” on the core discing process. The mechanical responses of the core, the borehole sidewall, and the bottom of the kerf were also contributing to this effect. Next, the simulations using different mesh sizes were conducted to achieve a best fit between the stress-strain curves and the failure modes. Finally, a method was introduced to eliminate the mesh size effects on rock discing in our numerical simulations. Keywords Core discing . Mesh size effect . Numerical simulations . Strain-softening model . Tensile failure . Shearing failure
Introduction Core discing has long been recognized as an indicator of high in situ stress in the Earth’s crust (Jaeger and Cook 1963; Ishida and Saito 1995; Lim and Martin 2010). The indirect estimate of in situ stresses based on core discing has become one of the important methods in deep tunneling projects (Li and Schmitt 1998; Kaga et al. 2003; Matsuki et al. 2004; Kang et al. 2006). Understanding the mechanisms of core discing with accurate simulations is a challenging issue. Jaeger and Cook (1963), Obert and Stephenson (1965), and Durelli et al. (1968) studied core discing mechanisms in a laboratory-scale setting. Obert and Stephenson (1965) considered the shearing effect as the main control factor accounting for core discing. In the 1980s, a comprehensive review of core studies was provided by Stacey (1982). To address the core discing issue, Song Responsible Editor: Zeynal Abiddin Erguler * Chuanqing Zhang [email protected] 1
State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610065, China
(1998) used a microscope apparatus to observe the failure modes of cores during the drilling process, and tried to explore the mechanism of core discing. In the aforementioned studies, most of them consider basically the tensile or extension cracking as the main control mechanism of core discing. Although there is no evidence that the shearing effect in this process can be excluded, the influence of shearing damage on core discing has not been fully unders
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