A theoretical model for rock joints subjected to constant normal stiffness direct shear

Abstract The authors have conducted an investigation into the behaviour of rock joints subjected to direct shear. Both concrete/rock and rock/rock joints were investigated. The behaviour of rock/rock joints is important for the assessment of stability issues involving rock masses (e.g. rock slope stability). Concrete/rock joints are vital to the assessment of performance of concrete piles socketed into rock, rock anchors and concrete dam foundations. This investigation included an extensive series of direct shear tests under a range of stress boundary conditions. The rock used for the tests was a soft artificial siltstone, called Johnstone. The results from the tests on concrete/Johnstone joints have been presented in Seidel and Haberfield (Geotech. Testing J. (2002), accepted for publication) and on Johnstone/Johnstone joints in Fleuter (MEngSc Dissertation, Department of Civil Engineering, Monash University, Australia, 1997) and Pearce (Ph.D. dissertation, Department of Civil Engineering, Monash University, Australia, 2001, in preparation). This paper describes the theoretical models developed to simulate the observed behaviour, including asperity sliding, asperity shearing, post-peak behaviour, asperity deformation and distribution of stresses on the interface. These models have been combined into a micro-mechanical simulation of joint shear. Comparisons between program predictions and measured performance are presented and discussed.