Analysis Of Deep Foundation Pit Construction Process Of Metro Station Considering The Coupling Effect Of Seepage And Stress

With the vigorous development of underground urban rail transportation,various deep foundation pit engineering problems continue to emerge.How to effectively control the deformation of deep foundation pits is the top priority in the design of foundation pits,especially for deep foundation pits in areas with rich groundwater.Construction is extremely difficult,so in the design stage of the deep foundation pit and the later on-site construction stage,we must pay attention to the impact of the dewatering and seepage effect of the foundation pit.This subject is based on the deep foundation pit project of the main structure of the Beidayingjie Station of Shenyang Metro Line 4 as the background,combined with the actual situation of the construction site,the construction technical plan and the on-site monitoring data,to organize and analyze the actual monitoring data on the spot,and use MIDAS GTS/NX established a three-dimensional model of the deep foundation pit,compared the simulated value with the actual monitoring data of the construction site,and verified the rationality of the establishment of the seepage-stress coupling model.Then the deep foundation pit supporting structure parameters and soil physical and mechanical parameters are studied,and the influence of the changes of the above various parameters on the deformation of the deep foundation pit is discussed,which provides a reference for the safe construction of the foundation pit.The main research results of this paper are as follows:(1)The finite element numerical models that consider the seepage-stress coupling and that do not consider seepage are established respectively.By comparing the calculated values of these two models with the measured values,it can be concluded that the simulated values of the various deformation indexes of the first model are the same.Compared with the second model,it is closer to the measured value on site,indicating that in actual construction,the effect of precipitation seepage has a greater impact on the deformation of the foundation pit,and it also proves the accuracy of the seepage-stress coupling model.(2)Comparing the field monitoring data with the simulated values extracted from the seepage-stress coupling model,it can be concluded that the surface settlement of each measuring point increases with the increase of the excavation depth of the foundation pit,and the excavation is unearthed in the foundation pit.After the end,the cumulative surface settlement reaches the maximum,and the maximum settlement point is between 5 and 8m away from the edge of the deep foundation pit.After the distance is greater than 8m,the surface settlement gradually decreases and becomes stable after 14m;In the initial stage of deep foundation pit excavation,the maximum displacement and deformation of the retaining structure of the underground continuous wall is located in the upper area of the middle of the underground continuous wall,and as the depth of deep foundation pit excavation continues to increase,the maximum deformation area will gradually move to the middle and lower part As a whole,the deformation trend of the two ends is small and the middle is large.The axial force of each layer of steel support also increases.Among them,the steel support at the top layer has a slower growth rate of axial force,while the second layer and The axial force value of the third-layer steel support has increased rapidly.Most of the steel supports have been installed for more than a month,and the change trend of the monitored axial force value gradually tends to a stable state.(3)Based on the seepage-stress coupling model,six factors including the size of the internal friction angle of the soil,the length of the uplift pile,the value of the axial force of the internal support,the thickness of the diaphragm wall,the permeability coefficient and the recharge measures are selected for research and analysis,The study found that: when the length of the uplift pile is about 30 m,the pre-added axial force of the internal support is doubled,and the thickness of the underground continuous wall is 1.2m,the effect of restraining the deformation of the foundation pit is the most obvious,and the cost-effective,Provide a certain reference value for the project.