Modelling the shear behaviour of sedimentary rock joints under constant normal stiffness conditions

The typical shear behaviour of rock joints has been studied under a constant normal load (CNL) or zero normal stiffness condition, but recent studies have shown that this boundary condition may not replicate more practical situations, and that constant normal stiffness (CNS) is a more appropriate boundary condition to describe the stress-strain response of field joints. In addition to the effect of boundary conditions, the shear behaviour of a rough joint also depends on its surface properties and the initial stress acting on its interface. Despite this, exactly how these parameters affect the shear behaviour of joints is not fully understood because the stress-strain response of joints is governed by non-uniform asperity damage and the resulting gouge that accumulates on their interfaces. Therefore, an attempt has been made in this study to predict the complete shear behaviour of rough joints incorporating the asperity deformation under CNS conditions. In order to validate this analytical model, a series of CNS shear tests were conducted on rough tensile (natural) joints and their replicas at a range of initial normal stresses that varied from 0.4 to 1.6 MPa. Comparisons between the predicted shear behaviour and the experimental results show close agreement.