Slope failure mechanism assessment based on regional geological information in layered rocks

Regional geological mapping commonly records the dip and dip direction of dominant layering such as bedding and foliation but not the orientation of joints. It is common for joints to form an orthogonal pattern relative to the dominant layering. In that case, the three-dimensional possibilities can be extrapolated allowing inferences to be made about kinematically feasible structural failure mechanisms. The resulting planar sliding, wedge sliding and toppling kinematic assessment can be integrated on a stereograph. The analysis of extrapolated joint sets can be conducted in the initial desk-top stage of a site investigation. The method is demonstrated using field data from Devonian sandstones in eastern Victoria, Australia. The sandstones have joint sets and partings on axial cleavage orthogonal to bedding. The range of potential structural failure mechanisms is extrapolated from the known bedding orientation and slope face direction.