Safety And Stability Analysis And Support Optimization Of A Deep Foundation Pit Excavation

With the acceleration of the pace of urban construction in China,the rapid growth of urban population density,the ground available space is increasingly reduced,traffic,environment,service and other problems continue to emerge,the application of urban underground space is more and more extensive.As the key link of urban underground space engineering development,deep foundation pit excavation safety problems occur from time to time.Therefore,reasonable analysis of the safety and stability of excavation process and optimization research of support have important engineering practical value.In this paper,taking the deep foundation pit project of West Square of Hefei University as an example,the finite element software Midas GTS/NX is used to conduct numerical simulation of the excavation and support process of the foundation pit,and the horizontal displacement,internal force change and settlement change of the surrounding surface of the support system are analyzed during the excavation process of the deep foundation pit,and the site monitoring is carried out.The accuracy and reliability of numerical simulation results are verified by comparing the results of numerical simulation and engineering measurement.Aiming at the existing problems of deep foundation pit supporting,instead of the brace support with anchor cable,and the orthogonal experiment design,numerical simulation of deep foundation pit supporting system optimization analysis,to explore under the different anchor parameters combination,mixed analysis of pile-anchor supporting system of deep foundation pit supporting system of horizontal displacement,ground subsidence,etc,The optimal pile-anchor cable parameter combination support scheme is obtained,and the optimized support scheme is constructed in the field,which further verifies the practical feasibility of the support scheme,and also provides reference for similar projects.The main conclusions are as follows:（1）Through on-site monitoring of the excavation process of the foundation pit of this project,the monitoring data are processed and analyzed.The results show that:with the increase of the excavation depth,the horizontal displacement of pile increases first and then decreases,and reaches the maximum near the pile depth of5.5m;The horizontal displacement of pile top reaches the maximum in the middle of the foundation pit edge,and the negative Angle is small.The surface settlement value around the foundation pit increases first and then decreases from near to far,and reaches the maximum at the distance from the foundation pit（6 ～ 10 m）.Axial force of inclined brace decreases gradually with the progress of excavation condition,and finally tends to be stable.Use the finite element software Midas GTS/NX to conduct three-dimensional modeling and numerical simulation for each working condition of foundation pit supporting structure.The results show that the horizontal displacement of pile increases first and then decreases with the increase of excavation depth.The horizontal displacement of pile top reaches the maximum in the middle of foundation pit edge.With the increase of the distance from the edge of the foundation pit,the surrounding surface settlement value increases first and then decreases.The settlement value reaches the maximum value 10 m away from the edge of the foundation pit.With the increase of excavation depth,the increment of axial force increases first and then decreases.（2）Using the finite element software Midas GTS/NX to conduct three-dimensional modeling numerical simulation for each working condition of the excavation support structure.The results show that the horizontal displacement of the pile increases first and then decreases with the excavation depth;The horizontal displacement of pile top reaches the maximum in the middle of foundation pit edge.The surrounding surface settlement value increases first and then decreases with the distance from the foundation pit edge.The settlement value reaches the maximum near 10 m from the foundation pit edge.With the increase of excavation depth,the increment of axial force increases first and then decreases.（3）The simulation results are compared with the monitoring results.The results show that the deformation trends of the horizontal displacement of the pile body,the horizontal displacement of the pile top,the surface settlement around the pile,and the axial force of the inclined support are all similar,and they are all within the 20%allowable error range,which verifies that the numerical simulation results are reasonable.（4）Through the design of 5-factor and 3-level orthogonal test,the results show that the diameter of anchor cable and its prestress have a significant impact on the safety and stability of deep foundation pit.The optimal parameter combination scheme is the pile distance of retaining pile 1.9m,pile diameter 0.9m,anchor cable prestress 80 k N,diameter 210 mm and Angle 15°.The results of the optimal scheme are compared with those of the original supporting scheme,and it is concluded that the optimized supporting system can effectively improve the safety and stability of deep foundation pit.Figure [63] Table [17] Reference [62]...