Shear Behaviour and Acoustic Emission Characteristics of Different Joints Under Various Stress Levels

Excerpt

Rock masses are typically characterised by faults, joints, bedding planes and other planes of weakness, and the mechanical behaviours (such as shear strength, stiffness, deformation and permeability) of jointed rock masses strongly depend on the mechanical and geometric properties of discontinuities. Shear failure along weak joints is one of the main failure modes in rock slopes and underground excavations; thus, understanding and predicting the shearing behaviours of jointed rockmasses are important for the design and stability analysis of rock structures. Patton (1966) proposed a bilinear strength envelope that describes the shear strength of saw-tooth joints well. Ladanyi and Archambault (1969) developed a new model by identifying the areas on the joint surface where sliding and breaking of asperities are most likely to occur. Based on a series of shear tests conducted on natural rough joints, Barton and Choubey (1977) introduced an empirical model that includes three index parameters: the joint roughness coefficient, the joint wall compressive strength and the residual friction angle. Zhao (1997) modified Barton and Choubey’s criterion by introducing the joint-matching coefficient. With the development of optics and data processing technology in recent years, the surface morphology of joints can be quantitatively investigated, and some new empirical criteria have been proposed by considering three-dimensional quantified surface roughness parameters (Grasselli 2006; Xia et al. 2014). Model materials (plaster, cement mortar) have mainly been used in previous studies to simulate rock joint, and the normal stresses applied were typically low as the burial depths of the engineering rock are generally shallow. Presently, the excavation depths of many tunnels extend beyond depths of 1000 or 2000 m, with high stress levels acting on the discontinuities. Therefore, it is important to understand the shear behaviour of joints under high normal stress. …