Van Sint Jan, ML & Prudencio, MG 2008, 'The Influence of Non-Persistent Joints on the Failure Modes of Large Rock Slopes', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium
, Australian Centre for Geomechanics, Perth, pp. 517-527.
Results of biaxial tests performed on models of rock with non-persistent joints show that, among other factors, the failure modes depend on the type of non-persistence: whether the joint ends in a rock bridge (non-persistency of type 1) or whether it ends in a differently oriented joint (non-persistency of type 2).
Three basic failure modes were found for type 1 non-persistency: planar failure and stepped failure are associated with large strengths, fragile behaviour, and small failure strain; whereas rotational failure is associated with a very low strength, ductile behaviour, and large deformation.
Step failure occurs when the major compressive principal stress is nearer the vertical and this mode controls the surface slope of the individual benches for the 800 m high west wall of the Chuquicamata mine; with separation on a continuous joint dipping back into the slope and sliding or toppling on the non persistent joint dipping into the excavation.
The major principal compressive stress in the lower slope of the mine is nearer the horizontal and can lead to a through-going failure along non-persistent joints and intervening bridges formed by large individual blocks with non-persistency of type 2. This failure mode was observed in the tests with individual blocks.