Study On Stability Of Stratum By Using Shield Tunneling Method With Neighborhood Tunnel

With the deepening of urbanization,in order to solve the phenomenon of urban traffic congestion,the development and utilization of underground space has become the needs of urban development.According to the definition of " neighborhood tunnels" in section 4.3.2 of "Specifications for Design of Highway Tunnels"(JTG_D70-2004)(in the case of soft rock sections,the spacing of two tunnels is less than 4B called neighborhood tunnels and B for tunnel widths),"Code for design of metro"(GB 50157-2013)provides that the construction of the shield tunnel parallel spacing between the tunnel should not be less than the diameter of the outer contour.But the mechanical shield construction and mountain tunnel construction of the new Austrian law is quite different,and the soil and rock properties are also quite different,in different stratum conditions,in the process of shield tunneling,the surrounding subsoil displacement and surface subsidence will inevitably occur in the urban subway tunnel construction,which will adversely affect the adjacent underground structures and ground structures,and cause a series of problems.Based on the project of Shijiazhuang Metro Line 1,Tangu Station and Chaohui Bridge Station,this paper uses the method of theoretical analysis and numerical simulation to study the influence of neighborhood tunnel which used shield tunneling method,in different strata,different distance conditions.The stability of rock and soil around the tunnel is studied.The finite difference simulation software FLAC3 D was used to simulate the disturbances of rock and soil around the tunnels with different stratum and spacing.The stress release method was used to simulate the tunnel excavation process.The soil around the tunnel was modeled by FLAC3 D.The elastoplastic model of Mohr-Coulomb criterion is used in the model.The linear elastic model of the concrete segment is adopted.Shell is used in shield segment.Null is used to excavate the soil.Observed the stress and strain,the plastic zone size and the deformation of rock and soil around the tunnel,and the conclusions are as follows:(1)With the decrease of the clear distance of the two parallel tunnels,the stress in rock and soil around the tunnel is increasing.When the clear distance is less than 1.0B,the increase of the stress in the rock and soil around the neighborhood tunnel becomes larger," Code for design of metro "(GB 50157-2013)stipulated in the shield method of construction of the tunnel between the net distance should not be less than the diameter of the tunnel outside the contour is reasonable.(2)With the increase of the clear distance of the two parallel tunnels,the subsidence of the rock and soil around the tunnel is decreasing and the rate of change is decreasing.But when the clear distance is more than 4.5B,the trend is increasing.In order to avoid the settlement is too large,the shield tunneling method should be as close as possible to 4.5B,but 4.5B of the clearance will produce a lot of underground space waste.Therefore,considering the space saving and other factors,we suggested that the net distance of about 2.0B is appropriate.(3)There are also some differences in the distribution of plastic zones in the neighborhood tunnels under different formation conditions.The stress in the cohesive soil is relatively large,while the silt and sandy soil are relatively small.In the application of shield construction of small clear distance tunnel,it should be noted that the construction of different rock and soil generated by the disturbance is different.(4)For different strata,neighborhood tunnel application shield construction caused by the settlement,are not the same.Among them,the cohesive soil is the simulation of the four kinds of rock and soil in the largest settlement,and the cohesive soil is one of the most commonly encountered in the soil,in the application of shielded soil construction method,to strengthen the tunnel Settlement monitoring,if found to have increased the trend of sedimentation,should be taken in advance to strengthen the soil corresponding measures.