Study On Deformation Law Of Soil And Rock Composite Strata Under Disturbance Of Subway Tunnel Construction

The soil-rock composite stratum is a kind of stratum frequently encountered in the construction of urban subway tunnels.Compared with ordinary single soil layers or rock layers,the deformation mechanism of soil-rock composite strata has its own characteristics.This paper relies on the complex of stratum and rock in Qingdao.In the construction of the subway project,based on literature review,on-site investigation,numerical analysis,on-site monitoring and other technical means,the deformation law of the composite rock stratum under the subway construction disturbance is studied in depth,in order to reveal the deformation mechanism of the composite rock stratum under the construction conditions of the subway tunnel.And provide a theoretical basis for the deformation control of soil and rock composite strata.The main research contents and research results of this paper are as follows:1.Through extensive literature review,collect the case of ground deformation under the disturbance of subway construction,obtain the risk factors affecting the formation deformation during the construction of subway tunnel,and analyze the deformation effect of the formation under the disturbance of subway tunnel construction from two aspects of time and space.The deformation mechanism during the construction of subway tunnels is analyzed.2.Based on the subway project under construction in Qingdao,based on the analytic hierarchy process,the sensitivity of the risk factors in the construction process of the subway tunnel was evaluated.The research results show that the subjective factors are the main reasons leading to the construction risk of the subway tunnel,among which,construction management Excavation methods,settlement deformation control,surrounding rock grades,surrounding structures and pipelines and ground loads are the main risk influencing factors in the construction of subway tunnels.3.Analysis of the soil rock tunnels under complex geological conditions of buried depth,rock mass and ground load the influence law of stratum subsidence,basically have the following main conclusions: on the ground under the action of load and the tunnel excavation effect coupling,vault subsidence above value increases with the increase of distance have been reduced,minimal subsidence on the earth-rock boundary;The level of surrounding rock has a significant influence on the subsidence in the soil-rock composite strata.The presence of ground load increases the amount of ground settlement,and the value of settlement deformation rate in the soil increases with the increase of load(from 0.18 to-0.98),while the deformation rate of rock remains basically unchanged(between 0.13 and 0.14).4.Based on the numerical method,the deformation law of soil-rock composite stratum underthe disturbance of subway tunnel construction is analyzed.The influence mechanism of subway tunnel construction process on soil-rock composite stratum and tunnel deformation law under different ground loading conditions is studied.The details are as follows:(1)Under different working conditions,the deformation laws on the interface of each layer are similar,and the affected area of each layer is about 40 m on both sides of the tunnel center line.Under the ground load condition,the deformation of each layer increases,and the increase of each layer gradually decreases with the increase of the buried depth of the stratum;“Stage I-Before Construction” and “Stage II-Construction” are the main settlements of each layer.In the stage,the proportion of the two-stage settlement decreases as the external load increases.(2)When there is no ground load on the surface,tunnel excavation plays a leading role in the deformation of the stratum.The closer the distance between the surrounding layers is,the larger the deformation is.As the ground load increases,the surface settlement increases significantly.In the construction process,the impact of ground load on surface deformation is emphasized.(3)Under each working condition,the vault settlement in "Stage I-before construction" and "Stage II-in construction" accounted about 75% to 84% of the total settlement,the amount of vault subsidence increased with the external load,the amount of settlement in each construction phase also increased with the external load,but "stage I." and " Stage II" settlement decreased with the increase of the ground load;The influence of the external load on the convergence of the tunnel perimeter is mainly in "Stage II" and "Stage III",and the proportion of the peripheral convergence of the holes in each stage is almost unchanged with the increase of the external load.The effect of the outer load on the subsidence of the vault is greater than that of the peripheral convergence.5.Selecting a subway tunnel in Qingdao as the supporting project,based on the on-site monitoring and measurement method,obtain the deformation data of the soil-rock composite stratum at each stage of the subway construction,and compare the numerical calculation results.The results show that the tunnel is in front of the tunnel.The main factors causing surface settlement caused by stratum disturbance caused by excavation.