Micromechanics of compressive failure and spatial evolution of anisotropic damage in Darley Dale sandstone |
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| Authors: | Xiang Yang Wu P. Baud Teng-fong Wong |
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| Affiliation: | 1. Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794-2100, USA;2. Institute of Geophysics, Chinese Academy of Sciences, Beijing, 100101, China;1. School of Mechanics and Civil Engineering, China University of Mining & Technology at Beijing, D11 Xueyuan Road, Beijing 100083, China;2. State Key Laboratory of Coal Resources & Safe Mining, China University of Mining & Technology at Beijing, D11 Xueyuan Road, Beijing 100083, China;3. State Key Laboratory for Geomechanics & Deep Underground Engineering, China University of Mining & Technology, No 1 University Avenue, Xuzhou 221116, China;4. Department of Civil Engineering, Monash University, Clayton, Melbourne, Victoria 3800, Australia;1. State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, China;2. School of Earth and Environmental Sciences, The University of Queensland, St. Lucia, QLD 4072, Australia;3. Chongqing Energy Investment Group Co., Ltd, Chongqing 401121, China;1. School of Engineering, The University of Warwick, Coventry, CV4 7AL, UK;2. Research Institute of Exploration & Development, East China Company of SINOPEC, Nanjing, 210011, China;3. Department of Geology and Geological Engineering, South Dakota School of Mines and Technology, Rapid City, 55701, USA |
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| Abstract: | ![]()
The micromechanics of compressive failure in Darley Dale sandstone (with initial porosity of 13%) was investigated by characterizing quantitatively the spatial evolution of anisotropic damage under the optical and scanning electron microscopes. Two series of triaxial compression experiments were conducted at the fixed pore pressure of 10 MPa and confining pressures of 20 and 210 MPa, respectively. For each series, three samples deformed to different stages were studied. Failure in the first series was by brittle faulting. In contrast, failure in the second series was ductile, involving shear-enhanced compaction and distributed cataclastic flow. In the ductile series, crack density and acoustic emission activity both increased with the development of strain hardening. The stress-induced cracking was relatively isotropic. In the brittle series, crack density increased with the progressive development of dilatancy, with spatial distributions indicative of clustering of damage at the peak stress and shear localization in the strain softening stage. Dilatancy was associated with significant anisotropy in stress-induced cracking, that was primarily due to intragranular and intergranular cracking with a preferred orientation parallel to the maximum principal stress. Compared with published data for Westerly granite and San Marcos gabbro (with porosities of the order of 1%) and for Berea sandstone (with porosity of 21%), there is an overall trend for the stress-induced anisotropy (in a sample deformed to near the peak stress) to decrease with increasing porosity. The sliding wing crack model was adopted to analyze the evolution of anisotropic damage, using a friction coefficient and fracture toughness inferred from stress states at the onset of dilatancy. Significant discrepancy exists between the model prediction and microstructural data on stress-induced anisotropy, which is possibly due to limitations intrinsic to the microscopy technique as well as the sliding wing crack model. |
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