Research On Influence Of Shield Tunnel Structure On Ground Heaped Load

Due to the development of urban infrastructure construction and the further exploitation of urban underground space,underground structures such as traffic tunnel and underground station inevitably become more and more intensive. So there appears a phenomenon that load and unload near the existing tunnel. Ground heaped load is a main factor which causes the deformation of existing shield tunnel. Furthermore, the large longitudinal and transverse deformation of the metro tunnel will lead to serious security problems of the tunnel's structure.This paper has adopted laboratory model tests as well as numerical analysis to study the deformation rules and deflections of shield tunnels in different burial depths underground heaped load of different positions and magnitudes, taking the characteristics of large diameter and great shallow-buried cross-river tunnels in saturated soft soil layer in Shanghai into consideration. The main achievements are as follows:(1) Whether ground heaped load is over or on the side of the existing tunnel, its magnitude is a main factor which causes the deformation. When the burial depth of the existing tunnel is within 3.5 times the diameter of the tunnel, the larger magnitude of the load is, the larger the deformation of existing shield tunnel will be. What's more, when the load is over the existing tunnel, the vertical displacement of the arch's apex reaches maximum length.(2) The burial depth of the existing tunnel is an important factor too. The additional stress of the soil around the existing tunnel becomes larger while the burial depth of the existing tunnel becomes shorter, so the deformation becomes larger accordingly. When the burial depth is 3m and the magnitude of the load is 20Kpa, the tunnel's deformation has been beyond allow value, so we define it as a limited field?; When the burial depth of the existing tunnel is within 1.5 times the diameter of the tunnel, ground heaped load has an conspicuous effect on the deformation of the existing tunnel, so we define it as a control field and attention field.(3) The load position is an important factor as well. The additional stress of the soil around the existing tunnel becomes smaller while the distance from load position to the centerline of the tunnel becomes longer, so the deformation becomes smaller accordingly. Otherwise the additional stress of the soil around the existing tunnel becomes larger while the distance from load position to the centerline of the tunnel becomes shorter, so the deformation becomes larger accordingly.