Close The Tunnel Below The Shield Construction On Existing Surface Subsidence And Deformation Of The Tunnel In Soft Soil Area

For Metro, the subway line has been changed by a separate complex subway network, with the formation of the MTR network, between the old and new underground structure of a route planning through the inevitable problems.Based on the Tianjin Metro Line 3, a range of surface subsidence caused by tunneling the measured data and theoretical calculation and finite element simulation, comparative analysis of the tunnel caused by the variation of surface subsidence; while soft soil layer for the case of Tianjin Binhai using the finite element software ABAQUS, etc. on behalf of the layer method used to establish shield tunnel model of three-dimensional numerical analysis of the construction of shield tunnel below the ground surface subsidence and its impact on the existing tunnel deformation, mainly the following conclusions:(1) Tunnel below have a greater impact on surface subsidence. Horizontally, the top surface of shield tunnel axis is most sensitive to vertical displacement, away from the axis of shield tunnel surface subsidence gradually slowed down, tunnel excavation can be ignored when the axis of the shield away from the location and depth of about 1.2 times more distant surface deposition; vertically, different levels of surface subsidence occurs, the more the more obvious away from the settlement of the shield tail, when 1.2 times the depth of the shield tail away from the outside, surface subsidence rate slowed down, stable settlement; with the face shield tunnel away from, beneath the existing construction of the tunnel gradually weakened, the surface vertical displacement field to the existing tunnel axis symmetrical distribution center, in the existing tunnel near the settlement of soil surface area of about 1.2 times the tunnel axis depth, away from the existing tunnel influence the soil surface area of about 0.7 times the tunnel axis depth; buried at different depths and below the surface, underground depth the greater the deeper the soil settlement, the more shallow depth, soil disturbance suffered by the lower level, the more moderate sedimentation rate; when the excavation face shield is in the existing tunnel below, the existing tunnel near the soil sedimentation rate decreased significantly, and the settlement small.(2) Tunnel below the deformation of the existing tunnel has a greater impact. When the excavation face in front of the existing tunnel axis horizontal distance of about 1.6 times the diameter of shield, both the tunnel began to be more pronounced vertical displacement, the maximum deformation of the axis in the top of shield, with the shield tunnel boring both the vertical displacement of the tunnel increases;away from the tunnel axis, the settlement decreases, subsidence trend slowing down, away from the tunnel axis of the shield diameter of about 3 times the position, the settlement is very small and can be ignored and outside the tunnel where both suffered deformation.(3) Not existing tunnel cross-section differential settlement. Existing tunnel from the tunnel axis the greater the more recent settlement, but little difference in the settlement of the same section, moving away from the end with the shield, differential settlement increases, the most obvious difference between top and bottom in the existing tunnel;when excavation face from existing shield tunnel axis diameter of about 1.2 times, both left and right ends of the tunnel settlement greatest difference occurred;with the advance of shield, left and right sides of differential settlement decreases, the biggest difference are still occurring in about two side, in addition to other locations around both ends of the settlement of differences have disappeared.