Abstract:  To further understand the impact of karst sinkholes on structural safety of Jiguanshan tunnel section from K72+220 to K72+340, the collapse scale of the karst sinkhole sidewall is estimated by combining the site survey results with the location and size of the underlying karst cavity. And then numerical simulations of karst sinkhole collapse are conducted by PFC3D to investigate the morphology of the karst sinkhole sidewall after the collapse. Based on the collapse simulation results, a typical crosssection is selected to establish a twodimensional finite difference model to analyze the impact of karst sinkhole’s collapse on the lining structural safety of Jiguanshan tunnel. The results show the following. (1) The collapsing body at the sinkhole sidewall will mainly load on the top of the karst cavity. The collapsed body volume is approximately 16 000 m3, and the impact force derived from the collapsed body is approximately 9.0×107 N. (2) The maximum deformation of karst cavity top induced by collapse of the karst sinkhole sidewall reaches 16 mm, which would make the safety factor of the lining structure at the left wall and the arch foot of the left line be less than 1.7. The overall average safety factor is still greater than the control standard, indicating that the impact of collapse and accumulation on the safety of the tunnel is limited.

Key words: Jiguanshan tunnel, karst sinkhole, instability and collapse, lining structure, safety evaluation, numerical simulation