Modelling Shear Behaviour of Joint Based on Joint Surface Degradation During Shearing

An empirical model of the shear behaviour of rock joints is suggested based on a recently proposed joint surface degradation investigation method. Plaster joint replicas were tested with various surface roughnesses, normal stresses, and shear displacements. Joint surfaces with identical joint surface roughness were tested under the same normal stress and the tests were stopped at different shear displacements to investigate the joint surface degradation during shearing. Moreover, the joint surfaces before and after the shear tests were digitized and the digital surfaces were aligned with the help of reference points attached to the sides of the specimens. As a result, the joint surface deformation and void space during shearing could be determined. An empirical model was built based on analysis of the failure mode and failure process of the joint asperities under shearing; the model also takes into account that the basic friction angle varies with normal stress acting on the contact area. The concept of the equivalent effective asperity dipping angle, d_e, which can be regarded as the representative angle along which the two surfaces slide, was proposed and employed in the derivation of the joint shear and dilation model. Additional shear tests were conducted to verify the proposed model by comparing it with the modified Barton model.