Abstract: To study the safety impact of cutting excavation unloading on the lining structure of operating tunnels, the demolition of a shallowly-buried neighborhood tunnel to a highway cutting project was taken as the research background. The Drucker Prager elastic-plastic constitutive model was used to analyze the evolution law of the deformation, stress and safety factor of the existing operating tunnel lining structure under the cutting excavation unloading by numerical simulation, and the safety impact zoning of the excavation and construction of the cutting was proposed. The results show that under the action of cutting excavation unloading and elastic resistance of surrounding rock, the tunnel floats as a whole and the walls on both sides squeeze inward, mainly vertical deformation. The maximum displacement at the arch crown is 36.77 mm. The tension region of the lining structure gradually expands from the invert upward to the vault. When the buried depth is 20m, the tensile stress reaches 3.47 MPa, and the arch foot is prone to stress concentration. The safety coefficient of the lining fluctuates greatly, and the minimum safety coefficient of the arch foot position is 1.91. In particular, it is necessary to strengthen the monitoring of the arch foot position. Referring to the code and the calculated value of each index of lining structure, the calculated residual buried depth ratio is used to divide the three zones with the impact of cutting construction on tunnel safety, and the construction suggestions for each zone are given.

Key words: tunnel engineering; tunnel demolition; cutting excavation unloading; neighborhood tunnel; lining structure; safety impact zoning

摘要： 为了研究路堑开挖卸荷对运营隧道衬砌结构的安全影响，以某浅埋小净距隧道拆除改建公路路堑工程为背景，采用Drucker-Prager弹塑性本构模型，基于数值仿真，分析了路堑开挖卸荷下既有运营隧道衬砌结构变形、受力和安全系数的演变规律，提出了路堑开挖施工的安全影响分区。结果表明：受路堑开挖卸荷和围岩弹性抗力作用，隧道整体上浮且两边墙向内挤压，以竖向变形为主，最大位移在拱顶为36.77 mm。衬砌结构受拉区由仰拱向上逐渐扩展到拱顶，埋深20 m时拉应力达3.47 MPa，拱脚易出现应力集中。衬砌结构安全系数波动较大，拱脚位置安全系数最小值为1.91，尤其需加强对两洞拱脚位置的监测。参考规范及衬砌结构各指标计算值，采用计算残留埋深比划分了路堑施工对隧道安全影响的3个分区，并给出各分区施工建议。

关键词: 隧道工程；隧道拆除；路堑开挖卸荷；小净距隧道；衬砌结构；安全影响分区