Comprehensive analysis of the surrounding rock mass stability in the underground caverns of Jinping Ⅰ hydropower station in Southwest China

摘要

The geological conditions of the underground caverns in the Jinping I hydropower station are particularly complicated, with high ground stress (the extreme value of the measuring point is 35.7 MPa), complicated deformation and failure mechanisms, and large unloading depth. The large deformation of the surrounding rock mass was beyond current engineering and academic understanding. During the construction period, the deformation and failure mechanisms were complex, and the unloading depth was large. The maximum deformation of the sidewall of the main powerhouse reached 246 mm. The monitoring results of multi-point extensometers basically converged two years after the completion of cavern excavation. Regarding the deformation and failure mechanism of the large underground caverns, the energy dissipation theory that can better describe the complex mechanical response analysis was proposed. The deformation failure mechanism, mechanical behaviour, supporting effect and stability evaluation of the large underground caverns were investigated from the perspectives of excavation unloading and energy dissipation and release. The excavation unloading-induced relaxation characteristics of the surrounding rock mass were analysed using a comprehensive approach incorporating the results of borehole television, acoustic wave testing, multipoint extensometer and numerical simulations. A criterion of the surrounding rock mass delineation incorporating the energy dissipation ratio, acoustic wave testing, wave velocity variation and elastic modulus variation was also proposed. Furthermore, the phenomena and law of deformation and failure of surrounding rock mass in the large underground caverns were revealed. The stability of surrounding rock mass in the underground caverns was evaluated. The related achievements can provide some references for similar deep underground rock engineering.