Numerical Simulation Analysis Of Continuous Wall Support Scheme Under Deep Foundation Pit

At present,the speed of urban development is getting faster and faster,and the horizontal developable space in the urban area is becoming increasingly tight.As a result,the underground space is being used more and more,and the underground construction depth is becoming larger and larger,and the requirements for foundation pit supporting engineering are becoming higher and higher.In our country,deep foundation pit supporting engineering is mainly theoretical design and site monitoring,while most traditional design methods adopt section design,which is not very perfect for the overall role of supporting structure,which is easier to make deep foundation pit retaining structure of underground continuous wall size thick,large section of the internal support structure,which will lead to increased difficulty in construction,construction period.A longer impact on the surrounding cultural environment of the project will also increase the cost of the project.In this paper,based on the example of a deep foundation pit supporting project in Nanjing,considering that the supporting structure design adopts the section calculation design according to the common engineering methods,and the overall function of the support in the underground diaphragm wall is slightly insufficient,the design checking calculation is completed by Lizheng deep foundation pit design software.The design values(lateral displacement of diaphragm wall and settlement around pit)are compared with the measured values.The numerical simulation modeling of deep foundation pit was completed based on MIDAS/NX software,and the rule of foundation pit deformation(lateral displacement of underground diaphragm wall,lateral bending moment of underground diaphragm wall,circumpit settlement and bottom uplift)was studied.The influence of three parameters of underground diaphragm wall thickness,internal support stiffness and embedment depth on foundation pit deformation was explored.The current support scheme of underground diaphragm wall is optimized to reduce the construction difficulty,shorten the construction period and save the construction cost on the premise of ensuring safety.This can also provide reference for similar foundation pit projects.The specific research results are as follows:(1)Through FSPW software,the design check calculation of the current support scheme is carried out.By comparing the maximum lateral displacement of the underground diaphragm wall and the settlement around the pit,the design value is obviously greater than the actual value.It is concluded that the design scheme of the underground diaphragm wall in the deep foundation pit meets the safety conditions,and the further design structure size optimization can be carried out appropriately.(2)GTS/NX software was used to conduct numerical simulation analysis of foundation pit excavation for foundation pit engineering examples,analyzing the development law of lateral displacement of underground diaphragm wall,lateral bending moment of underground diaphragm wall,circum-pit settlement and uplift of pit bottom.Meanwhile,comparing the measured value and design value,it was found that the simulated value calculated by finite element model was closer to the measured value.Compared with the design software,it can better predict the deformation of foundation pit during excavation.(3)In order to better satisfy the safety,efficiency and economy,the supporting structure parameters(thickness of underground diaphragm wall,stiffness of internal support and embedment depth of underground diaphragm wall)of the current foundation pit supporting scheme are changed based on the existing finite element model.The calculation results under the current supporting scheme are compared.The variation rules of lateral displacement of underground diaphragm wall,lateral bending moment of underground diaphragm wall and circumpit settlement are explored,as well as the sensitivity to the change of three supporting structure parameters,and the optimized supporting structure parameter scheme is given: 1.Compared with the current 1000 mm underground diaphragm wall,the wall thickness should be900mm;2.Compared with the current internal support section,which reduces the section area by10%;3.The embedment depth of underground diaphragm wall is changed to 1.8H compared with the current 2.0H(the above three kinds of optimization do not exist simultaneously).