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Abstract The surrounding rock mass of the underground caverns at Houziyan hydropower station is under high ground stresses and has a low strength-to-stress ratio，leading to severe rock deformations and failures in the process of construction. The deformation and fracture characteristics of the surrounding rock mass were analyzed according to the geological conditions，the data from monitoring and geophysical detection，and the construction process. The proportions of the measured points with the displacements greater than 50 mm in three main caverns are 17.2%，27.3% and 9.4% respectively. The deformations of the surrounding rock mass of the underground caverns are much greater than the ones of the underground caverns at other stations in the same period. The largest displacement is in the rock of category III1，which indicates that the deformation of rebound of the relatively complete and hard rock due to unloading under high ground stress are quite large. The depths of surrounding rock deformation reache 5 to 15 m，even up to 23 m. The deformation of surrounding rock was found to be closely related to the excavation with a stepped process of development. The deformation of the surrounding rock is largely stress driven with the stress redistribution playing the dominant role and the one to be gravity driven controlled by the adverse combination of structural planes played less roles.
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Received: 17 June 2014
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2014, Vol. 33 
