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Abstract In order to understand the spatial distribution of stress tensors of initial geostress field and to identify its relationship with the cavern group arrangement for hydropower plant site in high geostress region of deep valley，a new method and an operation procedure for obtaining a quantitative and fine numerical initial geostress field based on the coupling of 3D initial geostress calculation model and the structural calculation model containing excavation details were proposed considering the evolution process of river valley，using the space analysis method of stress tensor and the multi-core parallel computing technique. Then，the initial geostress field distribution at Jinping I hydropower station was identified with the method and verified against the field phenomenon of deformation and failure. The underground cavern groups of Jinping I hydropower station were found to be in the stress transitional region near the deep valley with the high geostress levels and the large stress variations and the high initial geostress environment was thus formed. The average principal stress ratio is about 1.9–2.5 and the rock strength-stress ratio is about 1.5–3.0 in this transitional region. Under the high initial 3D geostress，the low strength-stress ratio and the high principal stress ratio，the deformation and the failure and the depth of unloading relaxation of the surrounding rock during the construction of the underground powerhouse cavern groups were found to be larger than the ones of the cavern groups of the same size in other projects. The locations and distributions of the stress induced deformation and failure confirm the reasonability of the initial 3D geostress field obtained and also verify that the above proposed quantitative model of geostress field is correct and feasible. On this basis，a method of layout design for the underground powerhouse cavern groups located in high geostress area was proposed，considering the three-dimensional geostress，the strength to stress ratio and the structure characteristic，etc. The proposed design method reflects the load characteristics of caverns，the structure characteristics and the bearing capacity of surrounding rock. Using the above design method，some principles and procedures are put forward from a qualitative point of view，which includs how to determine the location of the main cavern，the longitudinal axis，the cavern spacing and type，etc.
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Received: 17 June 2014
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2014, Vol. 33 
