Extended key block analysis for support design of blocky rock mass

An extended key block method for rock mass stability analysis is proposed by considering the force effect of key blocks in later batches to the first batch which is exposed at rock mass surfaces. Through a realistic numerical representation of a three-dimensional rock mass, different batches of key blocks are searched by means of a progressive failure process. A force transfer algorithm is developed to consider the interactions of the key blocks in different batches. The calculated sliding forces in the first batch which consider the later batches' effect will lead to a better design of rock supports. After selection of a reinforcement scheme, the stability of the reinforced rock mass is re-assessed. Those larger instable blocks formed by inside blocks with anchored surface blocks are checked out. It is found that the two-step check of a reinforcement scheme, i.e. (1) safety check of the bolted individual blocks; (2) safety check of the bolted block groups is more effective. Results show that the proposed rock support design method is more realistic and rational for the reinforcement of blocky rock mass.