Study On The Advance Support Methods Of Shallow-buried Tunnels In Backfill Soil Layer Of Valley Topography

In recent years,with the improvement of environmental protection requirements,the development of western mountainous areas and the intensification of ground traffic congestion in big cities,tunnel projects have become more and more popular.During the tunnel excavation process,for the stable surrounding rock,the excavation surface and the excavated tunnel can be temporarily stabilized.However,for the weak and broken surrounding rocks,the excavation surface is difficult to maintain stability even if short footage is used for excavation.In the history of tunnel engineering,examples of tunnel collapse are not uncommon.For unstable rock systems,especially when tunnels pass through valleys with weak and broken surrounding rocks,the valley topography is mostly backfilled soil,soft soil,clay and mudstone,and the landform has large undulations.Due to the restriction of topographical conditions,tunnels are often shallow and have obvious bias pressure.Tunnel excavation will cause greater disturbance to the surrounding rock.Tunnel workers have studied many auxiliary stabilization measures,among which the pre-reinforcement and pre-support of the surrounding rock in front of the work are the key links to control and reduce the deformation of the surrounding rock after tunnel excavation and prevent collapse.So how to choose the appropriate advanced support for different weak and broken strata of the valley terrain has become an important research topic.This article focuses on how to select suitable advanced support for tunnels in valley terrain through different weak and broken surrounding rock formations.Combined with actual engineering cases,the geological model of tunnel passing through different strata is established and the finite element software is used to numerically simulate different working conditions.The advanced support effect of shallow tunnels passing through the surrounding rock of different strata in the valley terrain is compared and analyzed,and the best advanced support scheme and sensitive values of support parameters under the surrounding rocks of different strata are given.The main research contents are as follows:(1)Through a lot of reading and investigation of relevant documents and materials,and combining the characteristics of actual projects,three types of stratum models for tunnel crossing in valley terrain are established,and the deformation characteristics of surrounding rock are further studied.Research on the mechanism of common advance support measures is also carried out.(2)The finite element software is used to numerically simulate the supporting conditions of different advanced support measures in the tunnel passing through grade V surrounding rock stratum,soft soil layer,and backfilled soil layer.A total of 96 analysis conditions are selected for different parameters.The realization of the reinforcement mechanism of different advanced support measures in numerical simulation software is studied.The tunnel vault settlement,surface settlement and surrounding rock stress and deformation control conditions when advanced support measures are implemented in the same stratum are studied.The deformation control of surrounding rock under different supporting parameters for different advanced support measures in the same stratum is studied.The change of the advance support effect with the parameters is compared and the parameter sensitive values are finally selected.By comparing the supporting effect of different advanced support measures under the same stratum surrounding rock,the best advanced support scheme of each stratum is obtained.(3)Based on the body located in a shallow buried section of grade V surrounding rock of the Jinshan Tunnel in Yubei District,Chongqing City,the finite element numerical simulation of the formation is carried out by using the best advanced support method obtained from the above selection.The deformation law of surrounding rock obtained by simulation is analyzed and the original design and construction plan on-site monitoring and measurement data are then compared.This verifies the feasibility of the selection of advanced support methods in the different stratums of the valley terrain and provides a reference for future such projects.