Study Of Reinforcement Techniques For Foundation Of Sunken Square Over Subway Tunnels

With the advancement of the process of our modernization drive, the urban construction carry out on the ground and underground, the scene that the later excavation project have directly operation above the tunnel often occur, this is a new problem in the geotechnical engineering. The engineering which this paper studied belongs to the category. The excavation of large area close to the top of the tunnel, is likely to lead to a big displacement and deformation of the tunnel, even endanger the safety of subway’s operation. Therefore, it has become a problem urgently to be solved that how to accurately predict and reduce the deformation of subway tunnel caused by foundation pit excavation.On the basis of studying and summarizing the results of the relevant research at home and abroad, this paper build a numerical model in the finite difference software FLAC3D. Then according to the order of the construction organization, this paper calculation and analysis four different reinforcement scheme in the process of the excavation of foundation pit, then comparison and evaluation the effects of the four kinds of reinforcement scheme around the selected four indicators. The main conclusions of this paper are summarized as follows:1.A close foundation pit excavation above the subway tunnel will bring a significant impact to it, if do not take proper reinforcement measures, it will lead to a big displacement and deformation of tunnel, even endanger the safety of subway’s operation. The reason for this is that:excavation of foundation pit has intensified the results of unloading soil, enlarged the resilience value of soil, leading to an increase in displacement of the tunnel, especially the vertical displacement of the tunnel.2.Reasonable foundation reinforcement scheme can effectively reduce the effects of excavation to the tunnel. Cement-soil mixing piles cost low, have a certain reinforcement effect. Secondly, mixing pile is a holistic better space plate system, can enhance the soil’s constraints to the tunnel.3.The reinforcement scheme of uplift pile has a very significant effect in reducing the deformation of the tunnel. The main reason is that uplift pile has a longer body than others, it goes through the multiple layers at the bottom of the tunnel, which makes the work soil dose not only stay on the tunnel elevation position, the soil beneath the tunnel also has a certain reinforcement effect.4.1n the end, this paper chooses cement-soil mixing piles combined with uplift piles reinforcement scheme. Numerical analysis shows that, after adopting comprehensive reinforcement scheme, the vertical and horizontal displacement of the tunnel are less than the threshold, the minimum curvature radius of tunnel deformation curve is greater than the threshold, which meets the requirements of the relevant subway deformation control.