Research On Foundation Type Selection Of Subway Tunnel Under-traversing High-rise Building In Lanzhou Loess Area

In recent years,the construction of subways in cities in the loess region of northwest China has been increasing,and the situation that some buildings have been built in the planned tunnels under the subway has arisen.When the subway tunnel passes under the city,it will have an unavoidable impact on the surrounding soil,underground structures and surface buildings.At present,such researches are mainly concentrated in the large and medium-sized cities with more developed urban rail transit road networks but less targeted studies in the loess areas in the northwest.Thus,there are few research reports in Lanzhou city in the early stage of subway construction.This paper selected the Fanjiawan affordable housing project under the section tunnel of Lanzhou Rail Transit Line 4 as the object,systematically studying the foundation selection of high-rise buildings under subway tunnels in Lanzhou loess area.On the basis of the existing theoretical results,the characteristics and applicability of the common basic forms in the loess area as well as the influence of subway tunnels on the selection of high-rise buildings were summarized.The main research results are as follows:(1)The key points of foundation selection of high-rise buildings under multiple impacts are given according to the influence of subway tunnels.Reference criteria for foundation selection of high-rise buildings affected by metro tunnel underpass and reference criteria for foundation selection of high-rise buildings under loess conditions are proposed.(2)Through in-depth analysis of the background of Fanjiawan affordable housing project in Lanzhou and considering the influence of engineering geology,hydrological conditions,loess conditions and the tunnel underpass of line 4,two basic schemes are determined for the selected high-rise building research object.(3)The finite element analysis software MIDAS GTS NX was used to establish a 3D model of two basic schemes,and the simulation results were compared and analyzed.According to the results of numerical simulation,the optimum scheme is raft + cap + pile foundation.At the same time,the calculation method for optimizing the displacement of foundation scheme is given.Meanwhile,from the platform stress analysis of the preferred foundation scheme and the axial force analysis of the pile foundation,the optimization proposal of the plane layout and the increase of the pile diameter are obtained.(4)By using the single factor sensitivity analysis method,the numerical simulation of the soil layer parameters sensitivity of the preferred scheme was carried out.The results show that the optimal scheme is more sensitive to the parameters of the internal friction angle.