Preliminary design using block analysis for underground excavation in jointed rock

Block theory and related analytical technigues provide tools with which potentially unstable blocks are identifyed. These tools addressing problems of block identification and kinematic stability can be applied in the design process by screening the possible blocks so as to delimit the real key block. The relatively large number of blocks that are identified by joint pyramid analyses can be screened first on the basis of geometric data for the joints and the excavation, then on the basis of their frictional stability against sliding along one or two faces. The successive stages of the process are applied to a horizontal tunnel at Xiao-Lang-Di project to reduce the originally identified 14 admissible block shapes to 11 block shapes that kinematically able to fail, then to 7 shapes that are real key blocks that reguier further analysis.