Study On Excavation Deformation And Optimization Of Supporting Structure Of Deep Foundation Pit Under The Coupling Of Stress Field And Seepage Field

Relying on a rural drought-resistant emergency water diversion project in Xiaogan,Hubei Province,this paper uses Midas GTS NX finite element software to establish a three-dimensional deep excavation finite element calculation model for seepage-stress coupling,collates and analyzes the numerical simulation results,and organizes and analyzes the foundation pit monitoring data.First,the monitoring data are compared with the numerical simulation results,and finally the surface settlement curves of monitoring,simulation and numerical calculation are compared.In addition,by studying the effects of pile diameter,pile length,pile spacing and bolt spacing,bolt stiffness and bolt angle on the deformation of the foundation pit,the feasibility and interval parameters of the supporting structure are selected,and four of the above six factors have the greatest influence on the deformation of the foundation pit are selected,and the orthogonal experimental method is used to optimize the parameters of the foundation pit support structure,and the optimization scheme is obtained through range and variance analysis,and the final optimization scheme is compared with the original design.The main research contents and results of the paper are as follows:（1）This paper introduces the relevant background of foundation pit engineering,foundation pit deformation theory and seepage analysis.Combined with the engineering background,a three-dimensional finite element model of deep foundation pit excavation with seepage and stress coupling is established by using Midas GTS NX,and the calculation results are analyzed.The horizontal displacement curve of the retaining pile presents an overall"arch shape",and its maximum value is located above and below the 4m length of the retaining pile;The surface settlement curve generally presents a"groove shape",and its maximum value is about 17m away from the foundation pit edge;The uplift curve at the bottom of the foundation pit is"arched"as a whole,and its maximum value is located in the center of the foundation pit.（2）The design of foundation pit support is calculated by the software Lizheng,and the deformation of retaining pile and ground settlement meet the design requirements.The change trend of the horizontal displacement monitoring of the retaining pile is roughly the same as that of the simulation curve,and its maximum value is located at the retaining pile length of 5m and4m respectively;The variation trend of soil settlement monitoring around the foundation pit is roughly the same as that of the simulation curve,and the maximum values are located at 18m and 17m away from the foundation pit edge respectively.（3）The influence of supporting structure parameters on foundation pit deformation is studied.The horizontal displacement of retaining piles decreases with the increase of pile length,pile diameter and pile spacing;The lateral displacement of retaining pile increases with the increase of anchor spacing,decreases with the increase of anchor stiffness,and decreases first and then increases with the increase of anchor angle.The optimal pile length,pile diameter and pile spacing of the retaining pile are 13m,0.8m and 2.0m respectively,and the corresponding reasonable variation range is 11～13m,0.6～1.0m and 1.6～2.4m;The optimal spacing,rigidity and angle of anchor rod are 2.0m,1.25EI and 25°respectively,and the corresponding reasonable variation range is 1.6～2.4m,1.0～1.5EI and 15°～35°.（4）The orthogonal test method is used to optimize the design parameters of the foundation pit support structure.Through the range analysis and variance analysis,the order of the degree of influence on the foundation pit deformation is obtained:pile diameter>anchor stiffness>pile spacing>pile length,and the optimal design scheme is A₃B₁C₃D₃;That is,the pile length is 14m,the pile diameter is 0.7m,the pile spacing is 2.4m,and the anchor stiffness is 1.5EI.（5）According to the optimized design scheme A₃B₁C₃D₃ obtained by the orthogonal test method,the modeling calculation is carried out and compared with the original design results.Under the relevant design specifications,the maximum value of surface settlement is finally reduced by 28.29%,which has a good effect on the improvement of surface settlement;The maximum horizontal displacement of the retaining pile is relatively reduced by about 15.89%,which has a great effect on improving the horizontal displacement of the retaining pile and is within the control range.