Influence of cavern spacing on the stability of large cavern groups in a hydraulic power station

Many factors influence the static and dynamic stabilities of the rocks surrounding large cavern groups, such as in a hydropower station. In order to study the influence of cavern spacing on the stability of adjacent caverns, two kinds of dynamic-history simulation models for large cavern groups were set up by considering three different strengths of rock masses (soft rock, medium hard rock, and hard rock). One model included two caverns and the other included three caverns. The numerical simulations of these models were conducted under the loading of gravity and the combined loadings of gravity and earthquake motion, separately. To fully consider the dynamic features of rock masses, a damaged plasticity model with a non-associated potential flow was adopted for the surrounding rocks. Due to the stress redistribution and the scattering effect, simulated results indicate that, taking the caverns located in soft rocks, for example, if the spacing is less than one cavern characteristic length (taken to the biggest width of a cavern in the group), the static and dynamic responses of adjacent caverns are significantly affected by their spacing. The damage and the distribution of tensile stress surrounding the caverns are extremely extensive. Once the spacing approaches or exceeds twice the cavern characteristic length, the damage and the distribution of tensile stress of caverns keep unchanged, and the effect of nearby caverns disappears. In some situations, as the rock strength decreases, the damage becomes more severe and the area of tensile stress becomes more extensive. The critical distance of cavern spacing decreases as the strength of the surrounding rocks increases. The conclusions of this work could be used as a primary guidance to the anti-earthquake design for practical engineering.