岩溶天坑垮塌对下穿鸡冠山隧道结构安全影响研究

为深入了解下穿隧道结构安全受岩溶天坑垮塌的影响，以鸡冠山隧道K72+220~+340段工程为背景，结合现场勘察成果及下伏溶腔位置大小推测岩溶天坑侧壁垮塌规模，通过PFC3D数值模拟预测岩溶天坑的垮塌堆积形态。基于模拟结果，选择典型剖面构建岩溶天坑侧壁垮塌前后的二维有限差分模型，分析岩溶天坑垮塌对下穿鸡冠山隧道衬砌结构安全的影响。结果表明： 1）天坑垮塌后将主要堆积于天坑下伏溶腔的顶部，垮塌体量约为16 000 m3，垮塌体的冲击力约为9.0×107 N； 2）岩溶天坑垮塌将造成溶腔顶部最大变形达16 mm，并导致左线左边墙及拱脚部位衬砌结构安全系数可能小于1.7，但整体平均安全系数仍大于控制标准，天坑垮塌对隧道安全影响有限。

Impact of Karst Sinkhole Collapse on Structural Safety of Jiguanshan Tunnel

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.