A theoretical approach to predict the response of rock joints under the application of a shear load is required to minimize uncertainty in design calculations. Seidel and Haberfield, (2000) have developed a theoretical approach to estimate the shear response of the concrete/rock interface in pile rock sockets subjected to axial loading. Through laboratory testing, this work is being extended to the shear response of rock joints. A series of direct shear tests have been conducted on Melbourne Mudstone. Comparison of results from these tests with predictions from the shear model, show the potential of the theoretical model to predict rock joint behaviour.


A fundamental understanding of the behaviour of a rock joint under the application of a shear load is an important but difficult task in rock mechanics. Rock joints are known to be the weakest link in the rock mass and hence govern its strength. There are however many factors that affect the behaviour of a single joint. The applied stresses which can be insitu or induced, the boundary conditions which change according to the deformability of the surrounding rock, the roughness of the joint surface which is scale dependent, the rock type and strength, the joint wall strength, the type and extent of joint infill, the aperture, the presence of water and the shearing velocity have all been shown to be factors influencing joint shear behaviour. To successfully predict the shear behaviour, all these factors must be recognized and understood. Due to this complexity, empiricism has been relied upon in predicting joint shear strength. The JRC-JCS model developed by Barton, (1973) and later modified to include correction factors for scale (Barton and Bandis, 1982), wear (Barton and Bandis, 1990) and varying boundary conditions (Skinas et al., 1990), is perhaps the most popular predictive tool in use.

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