Deformation and cracking of an underground powerhouse cavern system under high in-situ stress
The properties of deformation and cracking of a large underground cavern system under high in-situ stress are analyzed based on its geology, the data from monitoring and geophysical investigation, and the construction process. Compared with the cases of low to medium in-situ stress, the deformation magnitude and EDZ depth are relatively large, and the proportion of deformation induced by rock fractures increases under high in-situ stress and low strength to in-situ stress ratio. At the same time, time-dependent deformation and rock spalling is obvious. The crack at the downstream arch is the unloading spalling and outward buckling failure of layered rock mass under the interaction of high in-situ stress and unfavorable geological structure. The circumferential cracks at the bus bar tunnels and connection tunnels were caused by the stress change and progressive failure of rock wall under the condition of low strength to stress ratio. As the deformation magnitude at the sidewall increases with the extending of EDZ depth, the time-dependent deformation is caused by the progressive failure of rock mass, which is different with normal creep deformation behavior of soft rock. The practice of the underground powerhouse cavern system shows that low pressure grouting is an effective way to control the evolution of deformation and rock failure under high in-situ stress.