A revised empirical method for predicting crack initiation based on Griffith strength criterion
LIU Quansheng1，2，WEI Lai1，3，LIU Xuewei1，LIU Jianping1，3，PAN Yucong1，3
(1. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China；2. Key Laboratory of Safety for Geotechnical and Structural Engineering of Hubei Province，Wuhan University，Wuhan，Hubei 430072，China；3. Graduate University of Chinese Academy of Science，Beijing 100049，China)
Abstract：Crack initiation stress is an important stress threshold in rock failure process. A better understanding of the rock failure mechanism can be obtained by studying its initiation criterion and a more reliable prediction of the rock properties can be acquired. The crack initiation tests on green sandstone from Chongqing under uniaxial and triaxial compression were conducted. The crack initiation mechanism and micromechanical feature were analyzed based on the multiple strain response，and it was found out that the induced tensile stress concentration caused by rock defects was the main reason for crack initiation. The initiation model of opening crack under the low pressure of confinements and the initiation model of sliding crack under the high pressure of confinements were obtained based on the above analysis. The maximum tensile stress around the rock defects was studied by employing the Griffith theory. The tensile stress increases as the deviatoric stress rises，which is strongly influenced by the friction effects under the high confining pressure. An empirical criterion of crack initiation prediction based on the different crack initiation patterns was proposed by introducing the parameter as the influence coefficient of the confining pressure. The parameter ，closely related to the internal frictional angle of rock，characterizes the friction effects in crack initiation，so the proposed empirical criterion can be applied to conditions of different confining pressures. The revised empirical criterion of crack initiation was verified with three sets of triaxial test on sandstone，granodiorite and granite，and its validity and applicability are much better than the conventional linear crack initiation criterion. It was also found that the crack initiation mechanism based on the analysis of is mainly tensile under the confining pressure of 60 MPa.
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2017, Vol. 36 
