| With the rapid development of urban construction in China,the population density of the city is increasing,and the available space on the ground is continuously decreasing.Rational exploitation and utilization of underground space has become an important way to solve this problem.Currently,the construction of subways is inseparable from the construction of foundation pits,especially the large deep pit construction of stations.The deep foundation pit of the urban metro station will have certain deformation during the excavation due to soil pressure,construction load and other factors,which will threaten the stability and safety of the foundation pit.Therefore,the deformation law of the deep foundation pit is understood and the base is predicted in advance.The deformation of the pit and the adoption of an effective foundation pit support scheme are essential to suppress the excavation deformation of the foundation pit.In this paper,by reading a large number of relevant literatures and materials,the deep foundation pit of a metro station in Hangzhou soft soil area is taken as a research example.The monitoring data of foundation pit excavation is studied and analyzed to summarize the law of foundation pit deformation.Based on the actual conditions of the project,the parameters of the foundation pit are determined.The geotechnical engineering software MIDAS GTS NX is used to simulate the excavation process of the deep excavation project,and the horizontal displacement of the retaining wall and the settlement of the ground surface under different excavation stages are simulated.The results were compared with the actual monitoring values,and the influence of different steel support parameters on the deformation degree of the foundation pit was also discussed.The research and analysis of this paper provides a certain reference value for the future deep foundation pit engineering of the subway.The main conclusions are as follows:(1)By analyzing the monitoring law of excavation site of foundation Pit,we know that the deformation of the wall of the deep foundation pit is shifted to the pit.The deeper the excavation,the greater the displacement of the wall,and the maximum displacement is about 0.7~0.8 times of the excavation depth.The surface settlement deformation curve is obviously groove type,and the maximum settlement is about 6m away from the edge of the pit.(2)Comparing the results of the simulation calculation with the results of the monitoring,the results show that the horizontal displacement and surface settlement values obtained by numerical simulation are smaller than the actual monitoring data,but the deformation trend is consistent,which indicates that the selection of the simulation parameters is Reasonable and reliable.(3)Increasing the stiffness of the steel support within a certain range can effectively inhibit the development of the wall level and the vertical displacement of the ground surface,and have little effect on the displacement change of the soil at the bottom of the pit,but the support deformation inhibits the deformation of the foundation pit when the stiffness is too large.The ability is weakened,and the results show that the influence of support on deformation is reduced when the original support cross-sectional area is more than 2 times.(4)Pre-stress should be applied immediately after the installation of the steel support in the deep foundation pit engineering.The deformation displacement when the axial force is pre-applied is significantly lower than when the pre-additional axial force is within the reasonable range,which is beneficial to the control support.It is advisable to change the system displacement and internal force when the pre-additional axial force is 60%~70% of the design value of the supporting bearing capacity.When the number of supported roads of steel support is small,it is not conducive to the stability of foundation pit,and no less than three steel support should be laid in this project in addition to the first layer of concrete support. |
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