Subway Tunnel Construction Caused Surface Subsidence And Deformation Studies

With the development of our country's transportation and the enlarging urban scale, many big cities have raised an upsurge of metro construction in order to solve the problem of increasingly serious traffic jam in cities. The construction of metro tunnel in cities will inevitably cause displacement and deformation of the ground. The oversize displacement and deformation of the ground will do serious damage to the ground buildings, pile foundations and underground pipelines. Domestic and foreign scholars have made a large number of researches on the displacement and deformation of the ground, and put forward many prediction methods. On the basis of forerunners research achievements, in this paper, their shortcomings are studied, and the displacement and deformation of the ground which are caused by tunnel excavation and dewatering are mainly researched. At the same time, the numerical simulation is conducted to study the impact of different construction methods on ground settlement of the shallow subway tunnel by excavation. The main contents of this paper include as follows:(1) Various settlement trough width formulas are studied. It is suggested that the O'Reilly&New formula is a universal formula, and the FLAC numerical simulation is conducted to validate it.(2) Curves between the ratio of maximal ground settlement and crown settlement and H/D in different settlement trough width formulas are drawed. The results show that the surface settlement predicted by Peck formula has bigger error when the ratio of tunnel depth and diameter is less than 1.5. So the applicable condition of Peck formula is the ratio is more than 1.5.(3) According to the principle of image method, the analytical solution of ground displacement is derived in which the non-uniform convergence of tunnel is considered. The advantages and disadvantages of Loganathan&Poulos analytical solution are studied synthetically. The analytical solution is modified by introducing a parameter related to the ground conditions. The modified formula is used to predict the ground displacement in five overseas tunnels. The results show that the predicted value has a good agreement with the measured data.(4) The calculation progress of the stochastic medium method which can be used to predict ground settlement and deformation is simplified. The result shows that the predicted values by the simplified method and the stochastic medium method are in good agreement when the ratio of tunnel depth and diameter is more than 3.0. This method is very simple, it is fit for single-hole, double-hole and all kinds of sections.(5) According to the geotechnical consolidation and seepage theory, the formulas of ground settlement caused by dewatering consolidation and seepage consolidation are derived respectively. They are validated by some engineering examples, and the results show that the formulas can well predict the surface settlement caused by the lowering of underground water levels.(6) Numerical simulation is conducted using finite difference software FLAC3D for shallow subway tunnel by excavation. The impact of different construction methods on ground settlement is mainly studied.