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Abstract Underground powerhouse caverns of Guandi Hydropower Station have the characteristics of high geostress and widely distributed discontinuities in hard surrounding rocks. Based on the characteristics analysis of geostress，rock mass structure and the conclusions derived from the monitored deformation data and the three-dimensional numerical simulation results，the deformation and failure characteristics of rock mass are summarized. The countermeasures for general layout design，excavation support design，construction of powerhouse caverns under high geostress condition are proposed based on systematical summarization. Following proposals are made for high geostress condition，such as the direction of the maximum principal geostress and the main discontinuities in the surrounding rock should be taken into account when the longitudinal axis of the chamber is chosen；adopting larger distance between the main chambers；adopting larger ratio of height to span of the top arch；adopting reasonable methods and sequence for excavation；improving the strength grade of shotcrete；delaying concreting the rock wall crane beam and the lining of busbar tunnels；determining reasonable initial prestress of the anchor cables. Also，for surrounding rock where rockburst is likely to take place，it is suggested that the initial steel fiber shotcrete with a thickness of 50 to 60 mm should be sprayed firstly；and then to install the systematical anchor bolts；finally to implement the designed remaining shotcrete with wire mesh. The above-mentioned proposals provide great guiding significances and application values for design and construction of similar underground powerhouse caverns under high geostress condition.
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Received: 30 September 2011
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2012, Vol. 31 
