Excavation response and reinforcement practice of large underground caverns within high-stress hard rock masses: The case of Shuangjiangkou hydropower Station, China

The construction of large-scale underground caverns poses numerous challenges due to their massive scale and high complexity. Among them, stability has always been a major concern during the construction process of large underground caverns within high-stress hard rock masses. It is not only influenced by the geological background of the project but also by the engineering activities during construction. This study takes the construction of the Shuangjiangkou (SJK) hydropower station as a case study and combines field investigations to summarize engineering issues and solutions under high geostress in three aspects. Firstly, it focuses on estimating and modifying the in-situ stress field of the underground caverns in the deep-cut valley area using limited geostress testing data and the observed failure phenomena in the pilot tunnel. Secondly, it discusses the typical failure phenomena of caverns under high geostress, including global stress-induced failures and local vein-controlled failures, as well as the corresponding failure mechanisms and treatment measures. Finally, it addresses the special failure phenomena occurring in the protective layer of the rock-anchored beam and optimizes the excavation scheme based on the observed failure patterns. The research results and solutions provided in this study, based on the case of the SJK hydropower station, are expected to serve as a reference for subsequent construction of large underground caverns within high-stress hard rock masses.