# Stability Analysis of Jinchuan Hydropower Station Hydraulic Tunnels during Excavation and Unloading
###### Abstract  
As the hydropower development strategies of China continue to be implemented, a host of large hydropower projects have been completed or are being constructed in southwest China. During construction of the Jinchuan hydropower station, this study examined the stability of the surrounding rock during the excavation and unloading of hydraulic tunnels under demanding geological conditions. Microseismic (MS) monitoring technology was employed to monitor the deformation and failure of the surrounding rock online and in real time, based on engineering geological data and site surveys. To analyze the stability of the surrounding rock in the spillway tunnel and to study the temporal and spatial evolution characteristics of MS events, source parameter analysis and numerical modeling were performed. The 3D finite-difference numerical modeling software FLAC3D was used to simulate the mechanical response of the surrounding rock during the excavation and unloading of the spillway tunnel and the diversion tunnel. The numerical modeling results were compared with the monitoring results and site surveys to determine the failure mechanisms of the surrounding rock during the construction and unloading of the hydraulic tunnels. The research results can serve as a guide for studying the stability of the surrounding rock in similar hydraulic tunnels.  
monitoring technique, MS monitoring has more advantages than the traditional monitoring techniques as it can detect micro-fracture signals before the macroscopic failure of the surrounding rock. It was initially employed for mine monitoring [7; 8; 9; 10] before being promoted and used in the oil and natural gas industries [11; 12; 13]. It was first applied in the field of hydropower engineering by domestic academics [PERSON] et al. [14; 15; 16; 17; 18; 19], and since then, the field has seen rapid development [20; 21; 22]. Many academics [23; 24; 25] have successfully built MS monitoring systems in hydropower projects such as Jinping-II and Baihetan, conducted in-depth research on engineering issues such as rock bursts and rock deformation, clarified the fracture mechanisms of the surrounding rock, proposed numerous warning indicators for rock bursts, and promoted the growth of geotechnical engineering disciplines. In recent years, the numerical calculation method has gradually become one of the main methods for analyzing rock stability in the field of geotechnical engineering.  
Numerical calculation methods based on computer technology have been applied in many fields as a result of the rapid advancement in computing efficiency. The following numerical methods are currently used in geotechnical engineering: the finite element method (FEM) [26; 27], finite difference method (FDM) [28], boundary element method (BEM) [29; 30; 31], discrete element method (DEM) [32; 33; 34; 35; 36], meshless method [37], discontinuous deformation analysis (DDA) [38], numerical manifold method [39], and infinite element method [40].  
Researching the safety monitoring and failure mechanisms of the surrounding rock during the excavation and unloading of underground caverns under difficult geological conditions is, therefore, a significant challenge in the prevention and control of underground disasters. In this study, based on the spillway tunnel of the Jinchuan Hydropower Station, MS monitoring technology was adopted to monitor the deformation and failure of the surrounding rock in real time, and source parameter analysis and numerical modeling were performed to analyze the stability of the surrounding rock in the spillway tunnel. This paper can provide a reference for the safe excavation of underground caverns in similar hydropower projects.