Study On The Safety Influence Of Rock-Soil Excavation Unloading Applied To Tunnel And Peripheral Structure

With the rapid development of urban construction,many existing transportation lines cannot meet the traffic demand brought by the rapid expansion of urban population,which hinders the urbanization construction and economic development.In order to solve this problem,road reconstruction is widely used in many cities.Urban tunnel is an important node of the line.In order to meet the demand of traffic volume,its reconstruction and construction plan often do not meet the conditions of completely closed construction.Therefore,phased traffic conversion should be implemented on the premise of sharing a certain traffic volume to complete the engineering reconstruction goal.In this process,the influence of soil excavation and unloading on the tunnel and its surrounding structure is an important basis for engineering design.In this paper,based on the Chongqing Lijihuayuan tunnel section reconstruction project,the finite element software was used to simulate the excavation process of the earth around the tunnel in the construction reconstruction process,and the stress distribution and displacement response of the surrounding structure were calculated.The analytical solutions of the additional stress and displacement of the tunnel were obtained by the traditional two-stage analysis method,and the traditional empirical coefficients and the calculation model were modified and optimized by comparing with the measured values and the finite element simulation values.According to the finite element simulation results,the original construction design scheme was evaluated and optimized.The main conclusions of this paper are as follows:(1)The finite element software ANSYS Mechanical was used to simulate the excavation process of soil around the tunnel,and the change law of stress distribution and displacement response of various structures was studied during the process.The results show that: in the original construction design scheme,the structural rebound displacement of Lijihuayuan tunnel and the shield tunnel of subway Line 6 is within the control range,and the whole system is safe and reliable.(2)The additional stress of the structure under excavation and unloading is calculated based on Mindlin stress solution,and the value of the initial residual stress coefficient is corrected by comparing the results.(3)The load-structure model is introduced instead of the beam model of the traditional elastic foundation to calculate the additional displacement of the structure under excavation and unloading.The results show that the calculation results of the load-structure model have better accuracy under the lithologic and geological conditions.(4)Based on the numerical simulation results,the original construction scheme is optimized.The results show that the control effect of surrounding rock pre-grouting on the rebound displacement of tunnel vault is not obvious.Increasing the height of earthwork excavation step and reducing the thickness of gravity retaining wall can save material cost and improve construction efficiency on the premise of ensuring engineering safety.The research results of this paper can provide reference for the construction design of similar projects.