Stability of large underground caverns excavated in layered rock masses with steep dip angles: a case study

The Wudongde Hydropower Station is constructed in layered strata that typically have steep dip angles. These features, together with the folds and faults that have developed in the strata, directly threaten the stability of the underground powerhouse. In this work, the behavior of the surrounding rocks under the original support measures is detailed in terms of rock mass deformation, anchor bolt stress, and extent of the excavation-disturbed zone, as obtained from safety monitoring and field testing. The characteristics of deformation and cracking of the surrounding rocks were also interpreted. To enhance rock mass stability, the support design and construction process were optimized and the positions liable to cracking treated. The efficiency of suggested scheme is verified by subsequent safety monitoring data and field testing. Then, a transversely-isotropic elastoplastic constitutive model for the layered rock masses was established. Numerical simulations are performed during the construction process to provide reference for decision making. The calculated deformations are in good agreement with the monitored values and they tended to be more stable. The plastic zones of the surrounding rocks fall within the range controllable using cables. Thus, the proposed measures are necessary and ensure sufficient stability. Finally, the mechanisms for the deformation and cracking of the surrounding rocks during the construction process are discussed. The work described aims to deepen our understanding of the mechanical properties of layered rock masses with steep dip angles and to improve the design philosophy.