Analysis of large deformation mechanism of the underground powerhouse at the Baihetan hydropower station

Abstract

Baihetan hydropower plant has the widest underground powerhouse and the largest scale of underground openings in the world. The surround rock mass of huge caverns is characterized by complex geological conditions and high in-situ stress of 30MPa. The monitoring deformation of the roof arch of the right bank powerhouse reached 165mm and the deformation of the side wall reaches 192mm, which had become the focus of the feedback analysis. In the paper, several field test methods, such as extensometer monitoring, grating fiber displacement monitoring, acoustic test and borehole image test, have been adopted to revealing the fracture expansion and time-dependent deformation of surrounding rock. Moreover, FLAC3D numerical simulation has been conducted integrated the monitoring results to analysis of large deformation mechanism. The results show that the combination of interlayer zone and high stress factors is the fundamental cause of large deformation caused by excavation. Finally, the reinforce measures and reinforcing range had been determined, and the stability of the powerhouse cavern has been evaluated according to the monitoring results for nearly 2 years after excavation. The studies, integrated the research approach of field geological survey, monitoring and numerical simulation, not only have shed light on the large deformation mechanism of excavation response of huge caverns, but also has provided a basis for dynamic optimization design and construction.