| The influence of unloading and its consequent elastic rebound on the shear strength degradation of bedding surfaces adjacent to surface excavations has not been widely acknowledged. In this study, footwall slabs exposed during surface mining were modeled using a 2D finite clement program. Joint boundaries simulated the slip surfaces along which the slabs were given freedom to slide. The effect of excavation unloading on shear strength degradation of bedding surfaces were evaluated by looking at the distributions of shear stress and displacement along the joint, yielded joint elements as well as the factors of safety for slab slip at different excavation stages. It was demonstrated that unexpected shear stress and displacement reversals occur along the slip surface as the slab is being passed by the pit floor. The modeling result provided new insights into progressive shear strength degradation that occurs when the pit floor approaches and passes footwall slabs. |
