Numerical Simulation Analysis of Initial Support Timing and Surrounding Rock Stability in the Underground Powerhouse of a Hydropower Station

The optimal support timing for the tailrace tunnel of a certain HSP was determined through the load release method. The results show that when the load release rate (LRR) of the surrounding rock (SC) reaches 80%, the deformation increment at the measuring points increases significantly, and this is the best support timing for this deep-buried tunnel. Taking the UP of this hydropower station project (HSP) as an example, the distribution laws of the deformation and stress of the SC of the underground powerhouse (UP) under the condition that the excavation LRR is 80% are obtained through the typical calculation example of three-dimensional nonlinear FEA. The results show that stress concentration is prone to occur at the top arch, bottom plate, and especially at the corners of the chamber. Therefore, enhanced support measures should be taken during the subsequent support construction.