Progressive failure analysis and support design of blocky rock mass based on extended key block method

Traditional rock support design methods of rock slopes and tunnels are reviewed. Towards a more rational support design, not only the effects of blocks inside the rock mass on the key blocks day-lighting into the excavation directly are considered, but also whether or not these day-lighting blocks are anchored to blocks inside and forming large key blocks after support is checked. Through a realistic numerical representation of three-dimensional rock mass, different batches of key blocks are searched successively. Then the sliding forces of the key blocks in the later batches are transferred to key blocks in the earlier batches batch by batch until the first batch according to a force transfer algorithm. The resultant forces of the key blocks in the first batch are finally utilized for support design. After selection of a rock bolting scheme, the stability of the reinforced rock mass is reassessed. Stability analysis of individual key blocks and block groups connected by rock bolts are carried out. Compared with the previous rock support methods, the present support design based on advanced key block analysis is safer and more rational for blocky rock support design.