Stress relief on hillsides and hillside excavations

The presence of high in situ horizontal stresses in the bedrock mass in Sydney is well established. The effect of stress relief during excavation into the bedrock mass is evident as horizontal movements as documented by a number of previous papers. This paper explores the likely stress relief on hillside slopes and the likely effect on movements during excavation. Two simple 2D block models are used to consider static equilibrium between the original in situ horizontal stress and the shear force possible on the base of the block. Published data in relation to stress reorientation or stress changes are summarised together with some observations in relation to site evidence of past movements which are indicative of stress relief on hillside slopes.