During the construction of large underground caverns under complicated geological conditions, reasonable mechanical parameters are the key to evaluating the mechanical safety and the behaviors of rock cavern. The method of intelligent loop recognition (ILR) is proposed for identifying mechanical rock parameters for large hydropower underground cavern. Considering the 3D spatial opening characteristics of large underground cavern, this method identifies equivalent mechanical parameters using multi-monitoring data and an intelligent algorithm at phase i opening of cavern. Then, the reliability of these identified parameters are validated at phase i+1 opening of cavern. The equivalent mechanical parameters are achieved after several excavation phases of cavern by circularly recognition. Application in the caverns of Jinping II underground hydropower station indicates that the proposed method is credible, and the identified mechanical parameters are both reliable and stable. This paper also proves firstly that the parameter of engineering rock is stable and can be acquired.
A series of large hydraulic power stations, including the Xiaolangdi, Three Gorge station, Eetan station, Laxiwa station, Xiluodu station et al., have been built in recent years. Obviously, more attention has been focused on the mechanical stability of underground hydraulic caverns due to uncertain rock environments[1–4]. In China, most hydropower resources are centralized in the western regions. In these regions, the Indian subcontinental plate pushes the Eurasian continental plate northward, thereby forming complicated terrains, deep valleys, and high mountains with rich water resources. However, extreme geological conditions in these areas always challenge the construction of hydraulic power stations, especially underground hydropower caverns. During the opening of large underground hydraulic caverns in tough geological environments, rock or support failure, such as rockburst, wall spalling, local falling, concrete cracks, and bolt breaks, always occur[5–8]. These failures in the opening of caverns result in serious safety issues for builders and require more understanding about rock performance during excavations. Meanwhile, uncertainty of mechanical rock parameters is the "bottleneck" in the evaluation and prediction of caverns' stability and mechanical behavior of[9,10].