Abstract: To understand the restraint of surrounding rock, vibration characteristics and evaluation standard of underground powerhouse structure, field tests and finite element analyses were conducted on a large pumped storage power station by using an electric testing method, to achieve the modal and dynamic response of underground powerhouse structure. Four types of finite element model are established according to different constraints between the upstream and downstream sidewalls and surrounding rocks. By comparing the results of finite element modal calculation and field test, it is found that when calculating the finite element modal of the underground powerhouse structure of the pumped storage power station, the reasonable calculating condition is that the boundary node of the powerhouse sidewall contacts with the surrounding rock in the normal direction. The deformation modulus of surrounding rock is selected according to the third type of surrounding rock, and the deformation modulus and Poisson's ratio are 10 GPa and 0.25, respectively. The elastic modulus of concrete should be calculated according to the dynamic elastic modulus. Through the dynamic response test of underground powerhouse structure, the maximum displacement is observed when the power generation is started or shut, which indicates that the start-up and shutdown of power generation are the most disadvantageous vibration conditions of underground powerhouse structure in normal operation of the pumped storage power station. The vibration caused by the start-up and shutdown of the power plant does not affect the stability of surrounding rock of the underground powerhouse, and the surrounding rock of the underground powerhouse is in a safe state. The frequency of dynamic response is mainly low-frequency components such as 0.5, 0.75 and 8.25 Hz that may be from the fluctuating pressure in the draft tube or spiral case and the basic frequency or frequency doubling of the unit, which means the vibration response of the underground powerhouse structure is mainly caused by the flow fluctuation and the unit frequency. Based on the safety assessment and analysis of underground powerhouse structure, it is suggested that 0.2 and 0.8 mm should be used as the evaluation criteria for the vibration control of underground powerhouse floor under steady and transient conditions, respectively. The anti-vibration performance of underground powerhouse structure basically satisfies the safety requirements. The analyses of finite element calculation and vibration tests of modal and dynamic response not only make up for the deficiency of the vibration test, but also provide a reference for anti-vibration design and vibration safety evaluation of underground powerhouse structure for pumped storage power stations.

Key words: pumped storage power station, underground powerhouse structure, restraint of surrounding rock, modal, dynamic response, evaluation criterion