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Abstract Aiming at the phenomenon of partial cracking and deformation of surrounding rock mass developing continuously at arch crown in the underground powerhouse，based on geology，monitoring data and construction process，qualitative analysis and quantitative analysis are made respectively combining with information of macroscopic deformation character and results of safety monitoring. The phenomena of collapse and crack occurred during the excavation of underground caverns is mainly formed by small unstable blocks because of stress distribution and blasting effect. Among the causes of its formation，the structure surface of fault and rock cracks is the main geological factor，and supporting lag is the main factor of construction. So considering the discontinuous characteristics of rock masses，it is important to take timely and effective support measures to ensure that surrounding rock mass of arch crown is in situation of stability. Parallel construction can speed up the construction progress in a certain extent，but it could have an effect on the displacement of surrounding rock. In the situation of parallel construction，although construction work has been far from arch crown，due to high construction intensity and frequent blasting，the displacement development of surrounding rock mass is still controlled obviously by construction schedule. So under the condition of complex geology，it is very necessary to avoid the parallel construction during construction process.
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Received: 29 May 2012
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2013, Vol. 32 
