Extended key block analysis for support design of blocky rock mass

• Published in: Tunnelling and underground space technology 2014-03, Vol.41, p.1-13
• Main Authors: Fu, G.Y., Ma, G.W.
• Format: Article
• Language: English
• Subjects: Algorithms; Applied sciences; Blocking; Blocky rock mass; Bolting; Buildings. Public works; Computation methods. Tables. Charts; Design engineering; Exact sciences and technology; Force transfer; Geotechnics; Instable block; Key block method; Reinforcement; Rock; Safety; Soil mechanics. Rocks mechanics; Structural analysis. Stresses; Support design; Three dimensional; Tunnels, galleries; Vector analysis
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2013.11.003

•The original key block methods are extended for more rational stability analysis and support design of blocky rock masses.•A force transfer algorithm is proposed to consider the force interactions of the adjacent batches of key blocks.•A two-step safety check is employed for the assessment of a selected rock bolting system.•Two examples showed that the later batches key blocks did affect significantly the sliding forces of some surface key blocks.•The two-step safety check is able to ensure the effectiveness of the bolting scheme. 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.