Abstract:

In tunnels and underground excavated in jointed rock masses at relatively shallow depth, the most common types of failure are those involving wedges falling from the roof or sliding out of the sidewalls of the openings. These wedges are formed by intersecting structural features, such as bedding planes and joints, which separate the rock mass into discrete but interlocked pieces. When a free face is created by the excavation of the opening, the restraint from the surrounding rock is removed. One or more of these wedges can fall or slide from the surface if the bounding planes are continuous or rock bridges along the discontinuities are broken. For this it was essential to carry out an analysis of wedges to better locate unstable blocks. Then, while taking into account the geometrical, mechanical data of the discontinuities as well as the geometrical data of the excavation, we were able to detect the shape and the size of the unstable blocks and the sets of discontinuities delimiting them and which favor their sliding and tilting. Thus, we calculated the number of anchor bolts needed to stabilize these blocks in order to ensure an acceptable safety factor. The paper uses a numerical simulation method by geotechnical software Rocscience-Unwedge 3.0 to analyze the influence of rock mass structure parameters on the stability of the wedge block when using the rock bolt. This study shows clearly how a wedge analysis of the rock mass can guide and optimize the support work