Study On Stability Of Dewatering And Excavation For Deep Foundation Pit Of Subway Station In Water-rich Soft Stratum

With the rapid development of urban subway construction in China,the scale of subway transportation network has leapt to the top in the world,and the construction of subway stations is an important part of subway construction,especially in underground water-filled soft soil areas,which has considerable Difficulty.Based on the foundation pit engineering of Sujiahang Station of Suzhou Metro Line 5,this paper studies the deformation and stability of deep foundation pits in water-rich soft soil layers.The site has complex geological conditions and high environmental protection requirements.In this paper,through the on-site monitoring,numerical simulation and other means,the three-dimensional numerical model is established by means of Midas-GTS NX finite element analysis software,and the influence of the supporting parameters of the foundation pit on the stability of deep foundation pit of water-rich soft soil is analyzed,and the strength is further combined.The reduction method makes a quantitative optimization analysis.The main contents and research results of this paper are as follows:(1)Combining the measured data of the foundation pit construction site and the numerical simulation results of Midas-GTS NX,the paper analyzes and summarizes the ground settlement,the horizontal displacement of the retaining structure and the variation of the supporting axial force during the foundation pit excavation and support,and obtains the foundation pit.The surface settlement curve conforms to the settlement groove curve in shape;the maximum horizontal displacement position of the wall of the enclosure structure also moves from the upper part to the middle part of the wall,which is characterized by small "bomb" type at both ends and four large axial forces.Generally speaking,the law of increasing first and then stabilizing is presented;(2)Using the Midas-GTS NX finite element software,the three-dimensional finite element analysis model of foundation pit excavation support is established by using MC model and MMC model under the condition of seepage-stress coupling,and combined with the measured data of construction site,comparative analysis The correctness of the two models and the rationality of the parameters show that the numerical results and trends obtained by using the MMC model to simulate the water-rich soft soil layer are closer to the measured values;(3)Exploring the influence of the length of the uplift pile at the bottom of the foundation pit,the support pre-axial force and the thickness of the retaining structure on the deformation of the foundation pit retaining structure and the surface soil,and quantitative analysis of the supporting parameters by the finite element strength reduction method.The influence of the variation on the safety factor of the foundation pit shows that the change of the length of the uplift pile has a weak influence on the stability of the foundation pit.Increasing the support pre-additional axial force multiple can effectively control the deformation of the foundation pit and appropriately increase the thickness of the foundation structure.The control of pit deformation is optimal.The research results of this paper will have certain guiding significance for the design,calculation and construction of deep foundation pits in the rich soft soil layer.