Most studies on strength criterion generally focus on the compressive strength rather than tensile strength. In fact, tensile strength is one of the most important mechanical properties of rock and also a significant controlling parameter of rock for engineering design. Based on the data obtained from the indoor rock experiments, four strength criteria are fitted to elaborate the various predictive effects on tensile strength. And the agreement between the predictive value of strength criteria and test data are discussed by the precise description of tensile strength, the minimum average standard fitting deviation and the main stress fitting curve. The results show that exponential strength criterion provided a comparatively precise description of the test value. Exponential strength criterion can be preferentially considered when evaluating rock strength characteristics under different stress states.
Rock strength theory studies the strength criterion of rocks in various stress states. Strength criterion, also known as failure criterion, which characterizes the relationship between the stress state under the failure condition and the rock strength parameters (Cai et al. 2002). Rock strength theory, the basic theory of rock mechanics, is always a hot issue in the field of rock engineering. Although numerous rock strength criteria and their modifications have been presented in literature, the limitation of their application seems always existent (Yu & Peng 2004, Shi et al. 2011). Therefore, it is necessary to argue the agreement between the predictive value of strength criteria and the test data by using the rock mechanics test results, thereby determining the applicability of the strength criterion.
The tensile failure of rock is one of the basic forms. Tensile strength of rocks is a significant mechanical index in design and construction of underground openings, because it indeed controls the stability of rock structure (Xu et al. 2004), and in engineering practice, tensile strength of rocks becomes an important criterion for evaluating the engineering stability (Zang & Su 2001). Most previous studies on rock strength criterion generally focused on compressive strength rather than tensile strength. You (2010) and Shi (2011) have compared the fitting precision of several criteria but without considering the rock tensile strength. Fu (2012) took rock tensile strength into account. However, he concluded that rock tensile strength has no significant effect on the fitting results of strength criteria. This is probably the reason why the study of rock tensile strength should be emphasized.