Abstract:

In the paper, the structural safety of the deeplyburied large crosssection tailrace tunnel of Huangjinping hydropower station is evaluated by means of numerical simulation and field monitoring. The result of this study shows: The tunnel is excavated in four benches, and Bench I is excavated by pilot tunneling method, i.e., the pilot is excavated before enlarging excavation is made. In this way, the disturbance to the deep surrounding rock is avoided, because the loose surrounding rock with low stress at the outer ring of the surrounding rock is excavated in the enlarging excavation. Therefore, the excavation method adopted is favorable for the structural safety of the tailrace tunnel. In the process of the excavation and supporting of the large crosssection tailrace tunnel, the maximum tensile stress and the maximum compressive stress of the surrounding rock are 0.86 MPa and 6.9 MPa respectively, and the maximum tensile stress and the maximum compressive stress of the supporting structure are 0.6 MPa and 5.0 MPa respectively. All of the abovementioned values are far less than the allowable stress values, and rock burst would not happen. The surrounding rock and the supporting structure reach stable gradually after the excavation and supporting are finished. The field monitoring results obtained by multipoint displacement gauges verifies the accuracy of the numerical results. The research method described in the paper can provide reference for similar projects in the future.

Key words: hydropower station, tailrace tunnel, large crosssection, numerical simulation, monitoring, structural safety