Relatively few experimental studies have been conducted on the scientific issue of progressive failure process of layered rocks with different dip angles of bedding (foliation). In this paper, the failure process of a gneiss with different schistosity dip angles has been studied under uniaxial compression based on digital speckle correlation method. The evolution nephograms of lateral strain field on the surface of samples have been obtained by the DSCM. The test results show that the progressive failure process of gneiss shows strong correlation with its internal schistose texture, i.e. it is significantly affected by the weak plane parallel to schistosity and its dip angle. More specifically, for the foliation angle β = 90°, the progressive failure process exhibits the characteristics of stable tension deterioration along weak plane. For β = 60° or 30°, the failure process is characterized by weak plane shearing and mutual competition. For β = 0°, the weakening effect of schistosity is not equally pronounced. The failure process exhibits the characteristics of stable tension degradation at the micro-structure plane.
In the fields of mining, water conservancy and hydropower, transportation etc., the surrounding rock mass is often classified as layered rock. The failure phenomena of rock mass induced by engineering activities are closely related to the anisotropic characteristics of its layered structure (Kim et al, 2016; Zhou et al, 2016; Xu et al, 2018a). The surrounding layered rocks of cavern will produce different deformation and failure modes under different layered angles. Therefore, it is particularly important to fully understand the failure process and mechanism of layered rock. Aiming at this scientific issue, most studies focus on investigating the mechanical behavior of layered rocks, such as slate, shale, schist and gneiss, by conventional triaxial tests, and assisted by means of scanning electron microscopy (SEM) and acoustic emission (AE) (Niandou et al, 1997; Duveau and Shao, 1998; Nasseri et al, 2003; Zhang et al, 2013). Additional studies include the failure modes at different layered angles by the Brazilian splitting tests (Dinh et al., 2013; Vervoort et al, 2014; Xu et al., 2018b). To a certain extent, these results reveal the mechanical behavior of layered rocks under the influence of bedding (foliation). However, there are few studies on the progressive failure process, including crack initiation, propagation and coalescence of layered rocks with different dip angles of bedding (foliation) under loading. Therefore, it is necessary to study the macroscopic and mesoscopic fracture mechanism of layered rocks under different dip angles of bedding (foliation) and to reveal the interaction between the dip angles of bedding (foliation) and the mechanism of crack initiation and propagation.
