Study On Disturbance And Zoning Of Influence Of Shield Tunneling On Shallow Foundation Buildings

The disturbance effect of the shield tunneling process in the soft soil layer on the buildings above the subway tunnel is evident.Moreover,the spatial position of the tunnel is very different from the interaction degree of different shallow foundation type buildings.Studying the spatial position effect of shield tunneling on the buildings above it is crucial for the safety of buildings and for the formulation of reasonable protection measures.Based on the typical soft soil layer,this study uses Plaxis^3Dfor the precise simulation of the process of a shield tunnel passing through different spatial positions underneath the buildings above it.This paper studies the relationship between single and double tunnel tunneling position L and different buried depth H and horizontal distance D,reveals the change law of surface settlement,explores the internal force and deformation law of different types of shallow foundation buildings above in the process of shield tunneling,and based on the composite criterion and the strength subtraction method,the safety influence range of shield tunneling in the soft soil is studied.The main research results are shown as follows:（1）The numerical simulation study is carried out for the single-track shield tunnel under three different shallow foundation buildings in typical soft soil environment in Shanghai,This paper summarizes the surface settlement deformation and building deformation rules when the tunnel is in different spatial positions under the building.The results show that the change of axial force of the building is mainly reflected in the building plate structure,while the change of shear force and bending moment is mainly reflected in the building column structure.For the tunnel underpass,different foundation types of shallow buildings have different ability to resist deformation.Under the same tunneling conditions,the box foundation has the strongest resistance to settlement of the lower tunnel tunneling,and the raft foundation has the strongest resistance to tilt due to the lower tunnel tunneling.（2）The numerical model of the shallow foundation building under the double-line tunnel with different burial depth,horizontal spacing and construction sequence is constructed.By analyzing the displacement of each monitoring point under different working conditions and the internal force changes of the slab and column structures of the building,the law of surface settlement and the law of deformation and stress of the building when the double-track tunnel is under crossing are obtained.The"blocking effect"or"disturbance effect"produced by the previous construction tunnel on the later construction tunnel during the construction of double-track tunnel can affect the distribution of disturbance area to a certain extent,therefore,the curve shape of the settlement groove and the influence effect on the building of the double-line tunnel are greatly different from that of the single-line tunnel.（3）The strength reduction method is used to calculate the safety factor of the numerical model,and the variation law of the safety factor of surrounding concrete lining,with or without the building load is obtained.The influence of the building load on the tunnel construction is reflected by the relative ratioξof safety factor in this case.For a single tunnel,ξ=78%is used as the dividing boundary between the strong and weak influence areas of a seven-story building,ξ=82%is used as the dividing boundary between the strong and weak influence areas of a ten-story building,andξ=86%is used as the dividing boundary between the strong and weak influence areas of a thirteen-story building,takingξ=95%as the dividing boundary between weak influence area and no influence area,the strong,weak and no influence areas are divided.For the double-line tunnel,the safety factor of left and right double track tunnels and upper and lower double track tunnel is calculated at different spacing and different building load,and the variation law of the overall safety factor is also summarized.