Study on seismic response characteristics and failure mechanism of giant-span flat cavern

In order to study the seismic response characteristics of the giant-span flat cavern (GSFC), a nonlinear finite element model of the GSFC was firstly established by ABAQUS software to investigate the seismic deformation characteristics and stress variation law of the GSFC in detail. Secondly, the bearing mechanism of the GSFC was systematically analyzed. Finally, the damage evolution law and failure mechanism of the GSFC were revealed. The results showed that the deformation, stress and damage of the GSFC under design and rare earthquakes were within safe and controllable limits. The interaction between the linings had a certain damping and peak -elimination effect. When the PGA was 0.2 g, the peak acceleration of the inside lining was reduced by 10% compared to the outside lining, the deformation response was reduced by 39%, and its seismic stress distribution was more uniform. In the bearing system of the GSFC, the surrounding rock was supported the lining so that its self-bearing capacity was fully utilized, while the lining was embedded by the surrounding rock, improving its integrity and stiffness. Under extreme earthquakes, the damage evolution processes of the surrounding rock and the lining were coupled with each other. The continuous plastic strain occurred mainly at the bottom and top of the surrounding rock. The outside lining was mostly destroyed, and the inside lining gradually degraded into a double-hinged arch structure supported by the side walls, so that the seismic performance of the surrounding rock-lining bearing system was lost. The degraded structure can maintain a relatively stable vertical self -equilibrium state and is not prone to extreme damage such as overall collapse. The research conclusions could provide a theoretical basis and scientific reference for accurate seismic prediction and safety evaluation of the GSFC.