Evaluation of Shear Strength Parameters of Rocks by Preset Angle Shear, Direct Shear and Triaxial Compression Tests

Excerpt

Estimation of shear strength parameters, which are generally known as the cohesion and internal friction angle (c and φ) in the Mohr–Coulomb (M–C) strength criterion, plays an essential role in rock mechanics and rock engineering (Zhao 2000; Kahraman et al. 2006; Alejano and Carranzatorres 2011; Gong et al. 2016). These parameters are often utilized to assess the damaged zones in rock masses around an excavation and the corresponding support design in engineering practices (Srivastava and Singh 2015; Wu et al. 2018). Determination of c and φ is the basis to estimate the mechanical properties of a specific rock material using the M–C strength criterion. Various researchers have expanded some of the early works concerning the cohesion and friction angle (or angle of resistance) of rock materials. Preliminary investigations on these two shear strength parameters were mainly conducted via direct shear (DS) and triaxial compression (TC) tests in laboratory (Dieterich 1979; Lajtai and Gadi 1989; ASTM 1996; Li et al. 1999; Ramamurthy 2001; Han 2001; Jiang et al. 2004; Barla et al. 2010; Konietzky et al. 2012; Yazdni 2012; Wu et al. 2014; Dang et al. 2016; Gong et al. 2019), or by using other newly developed estimation techniques (Hajdarwish and Shakoor 2006; Jia and Shi 2011; Armaghani et al. 2014; Karaman et al. 2015; Shen and Jimenez 2018; Kalantari et al. 2018). In the above-mentioned studies, some were focused on the development of shearing techniques (e.g., Jiang et al. 2004; Barla et al. 2010) and some others were focused on the application of shear strength parameters (e.g., Armaghani et al. 2014; Karaman et al. 2015). In fact, various experimental methods have been used to determine c and φ for specific rocks. Recently, the three main shear test methods for rock materials include the preset angle shear (PAS) (Xie et al. 2007, 2008; Wang et al. 2016), the DS (Jiang et al. 2004; Barla et al. 2010), and TC (Ramamurthy 2001; Yazdni 2012) tests. Zhang and Liao (1997) compared and explained the differences in measured shear strength parameters from the perspective of the M–C criterion strength theory by conducting a series of DS and TC tests on six types of rock (coarse-grained sandstone, medium-grained sandstone, fine-grained sandstone, limestone, shale and coal). A significant difference in the shear strength parameters from DS and TC tests on red-bedded soft rocks was also shown by Zhou et al. (2005). In addition, some studies have explored the evolution and mobilization of shear strength parameters during rock deformation or failure processes (Zhang et al. 2014, 2015; Renani and Martin 2018). …