Study On Stress And Deformation Characteristics Of Diaphragm Wall Enclosure Structure In Nanjing Yangtze River Floodplain

Foundation pit engineering has strong regional characteristics,and it has different characteristics and difficulties,according to different engineering geology,hydrology and surrounding environment.In the east coastal areas,the Yangtze River alluvial plain area of soft water-rich soft soil area,the foundation pit is accompanied by greater displacement and deformation in the process of excavation,it has a greater impact on structures,pipelines and roads around the foundation pit.In the water-rich soft soil layer,the diaphragm wall enclosure structure reflects the advantages that other foundation pit supporting structures can not match,and has the functions of seepage prevention,water interception,soil retaining,skid resistance,etc.And its own stiffness is large,integrity is good,the foundation pit deformation is small,the surrounding soil settlement is small.This paper combines with the practice of deep foundation pit engineering in soft soil layer rich in water in Nanjing Yangtze River floodplain,and the theoretical analysis,field test and numerical simulation are used to study the stress and deformation of diaphragm wall enclosure structure during excavation.The main research contents and conclusions are as follows:(1)The horizontal displacement and soil settlement of underground diaphragm wall enclosure structure in soft soil layer with rich water in Nanjing were monitored.The results show that the maximum lateral horizontal displacement of diaphragm wall increases gradually with the excavation depth,the increasing amplitude of displacement gradually decreases with the excavation depth,and the relative lateral displacement decreases with the excavation depth.The lateral displacement of diaphragm wall first increases and then decreases with the excavation depth,and then tends to be stable and decreases to zero.The lateral displacement pattern of the wall presents an "inner convex" deformation pattern,and the surface settlement curve on the side of the foundation pit is parabolic.(2)The finite element software ABAQUS was used to model the foundation pit project in the Yangtze River floodplain area in Jianye district,Nanjing City.The deformation law of diaphragm wall with horizontal support and without horizontal support is compared,the simulation results show that the stiffness of diaphragm wall is relatively large,which can effectively reduce the lateral deformation of wall under soil and water pressure.Compared with no support of underground continuous wall of palisade structure level,set the level of support,the soil on both sides of the horizontal displacement of foundation pit has been effectively limits,the integral lateral stiffness of underground continuous wall,vertical direction of each location of the foundation pit horizontal displacement has a certain degree of reducing,and can effectively reduce the wall inside to overthrow.(3)Python language is used for programming,the solution domain is determined,the solution domain is discretized,the element matrix is derived,the element matrix is assembled,the simultaneous equations are used to solve the node information,and the element information is calculated from the node information.By inputting the support and excavation depth in the self-programmed program,the relevant information can be solved,and the deformation and displacement of diaphragm wall can be output.The results of the self-programmed program are compared with those of Qiming commercial software.The results are close to each other.The maximum displacement error of the wall is 20%,the bending moment error of the wall is less than 25%,and the overall error is controlled within a reasonable range.