An Innovative Sampling Method for Determining the Scale Effect of Rock Joints

Excerpt

The mechanical behaviour of rock masses is governed by the properties of intact rocks and discontinuities among intact rocks, such as bedding planes and joints, of which the latter play a more significant role in many failure phenomena of jointed rock masses (Huang et al. 2016; Tang et al. 2017). It is well known that the mechanical behaviour of rock joints can vary remarkably with their size (e.g., Swan and Zongqi 1985; Re et al. 1997; Fardin et al. 2001; Tatone and Grasselli 2013; Yong et al. 2018a). The mechanical parameters, such as the shear strength and dilation angle, determined by testing rock joint samples with typical laboratory sizes might be unrepresentative of in situ structures, such as rock slopes and deep underground openings (Jiang et al. 2006). Numerous studies have been carried out over the last several decades to explore the scale effect on the shear behaviour of rock joints (e.g., Barton and Choubey 1977; Bandis et al. 1981; Barton et al. 1985; Hencher et al. 1993; Ohnishi et al. 1993; Johansson 2009; Hencher and Richards 2014). Some of these studies, however, have produced conflicting results (Leal-Gomes and Dinis-da-Gama 2010). According to the study by Bahaaddini et al. (2014), the scale effect can be categorised into three types: (1) positive scale effect, which shows that the shear strength of rock joints increases with the sample size; (2) negative scale effect, which shows that the shear strength of rock joints decreases with the sample size; (3) no scale effect, which means that the shear strength does not change with the sample size. Consequently, the mechanism of scale effect on the shear strength of rock joints is still unclear or speculative, suggesting a need for further investigations. …