Underground Caves, Tunnels and Excavation of Hydraulic Power Station

Underground caves, excavations or underground openings pose fundamental problems in rock mechanics and geotechnical engineering (Brady and Brown, 1985; Goodman, 1989; Wittke, 1990; Hudson and Harrison, 1997; Sun, 1999; Harrison and Hudson, 2000; Zhou and Yang, 2005). Underground opening includes mines, shafts, tunnels (drifts), hydraulic power plants and chambers for the military, for storage of foods, chemical products, oil and natural gas and for other civil, industrial and war applications. Underground excavation breaks the equilibrium of the original stresses in the rock or soil and causes a redistribution of stress in the surrounding rock or soil. The stress state of an underground circular cave or tunnel is shown in Fig. 10.1. The surrounding rock (or soil) is acted upon under the vertical stress σ y and the horizontal stress σ x .