| According to international experience,metro construction enters an explosive period when the urbanization rate is around 60%.China is entering the inflection point period and is more suitable for the development of urban rail transport,and metro construction is entering a peak period.The planning requirements of the metro are to solve the traffic problems in concentrated urban areas,which determines that the metro stations will be located in densely populated old urban areas with complex pipelines,narrow construction sites,and dense traffic around these areas.In the actual project,the deformation of the foundation pit has led to instability,resulting in huge economic losses and even casualties.Therefore,the monitoring and deformation analysis during the excavation of the foundation pit is very important.In this paper,we simulate the whole process of semi-cover excavation of the Qingshan junction metro station,compare and analyze the key monitoring data,numerically simulate the excavation process of the project using the reverse method,and analyze and compare the simulated data.The main research contents of this paper are as follows:(1)The deformation of the enclosure structure,the settlement deformation of the soil around the surface of the foundation pit and the uplift deformation of the foundation are introduced in the deep foundation pit project,and the influencing factors and related control measures are introduced.The project deformation monitoring data are summarized by items,and the analysis shows that the surface settlement of cover excavation measurement is larger than that of open excavation side;the maximum value of horizontal displacement of ground connection wall is larger than that of open excavation side,and it shows bow shape with depth;the column settlement leads to the trend of decreasing with time or excavation of foundation pit.(2)Based on MIDAS/GTS NX,a semi-covered excavation model of the station was established and compared with the engineering monitoring data to analyze and verify the deformation pattern of the foundation pit: the trend of surface settlement on both sides of the foundation pit showed a groove shape,and the closer to the edge of the foundation pit,the larger the settlement value and there would be a sharp increase in the settlement value at the beginning of the excavation of the foundation pit;the uplift center at the bottom of the foundation pit was influenced by the position of the column and showed a deviation from the direction of the column,and the overall uplift value showed a large middle and small sides.(3)Establishing the station reverse excavation model,it is concluded that the horizontal displacement of the enclosure structure during the construction of the reverse method is smaller on the west side of the pit than on the east side,and the deformation of the reverse method is reduced by 23.7% on the east side and 39.1% on the west side compared with that of the parallelogram method;the surface settlement deformation of the reverse method is reduced by about 1/4,and the settlement range of the soil body on both sides is about 38 m,which is 50 m compared with that of the parallelogram method.The influence of the inverse method on the soil around the foundation pit is relatively larger.The base uplift value of the inverse method increases continuously with the steps,and the maximum uplift value is reduced by about 1/3compared with the by-product method.(4)The comprehensive analysis of the semi-covered excavation method and inverse method shows that the semi-covered excavation method has advantages in controlling the construction period,cost and construction difficulty compared with the inverse method,but the inverse method has more advantages in controlling the surface settlement deformation and the displacement of the enclosure support structure in the deep foundation pit project,which can ensure the safety of the whole excavation process in the deep foundation pit project of the complex surrounding conditions of the subway station. |
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