Research On The Optimization Of The Supporting Structure Of The Deep Excavation Foundation Pit By Open Cut Method In The Exit Of A Imin Tunnel Of The Hamu Passenger Dedicated Line

The design of support for deep foundation pits involves many aspects such as quality and safety,construction cost,and construction period.It is an old and continuous innovation issue.For different geological conditions,hydrological conditions and surrounding environmental conditions,it is necessary to provide a targeted structural support scheme suitable for excavation of deep foundation pits in the area.How to choose a reasonable support structure is still a problem worthy of discussion.Foundation pit excavation is a complex and systematic project.Especially when the local conditions and hydrological conditions are poor,it involves geotechnical engineering,drainage engineering and structural engineering,etc.,and is increasingly being weighed by engineering and technical personnel.The design of foundation pit support must meet the requirements of strength,deformation and stability.Secondly,the economic benefits and rationality of the project must be taken into consideration.This requires a reasonable choice and optimum design of each feasible scheme.Therefore,the reasonable choice of support schemes,the improvement of project quality,and the reduction of engineering accidents raise higher requirements for the optimal design of foundation pit support schemes.This paper combines the supporting structure of the deep excavation foundation pit by open cut method in the exit of Aimin tunnel of the Hamu Passenger Dedicated Line.Through on-site monitoring and theoretical analysis,the optimization study of the foundation pit supporting structure is carried out.The main research contents are:(1)Analyzed the research background,significance and development trend of deep foundation pit engineering,summed up the research status at home and abroad,briefly explained the types and theoretical calculations of the long deep foundation pit,and briefly analyzed the foundation pit engineering.Common accidents.Through consulting and researching relevant data,some common foundation pit support forms and their applicable conditions are summarized,which provides theoretical guidance for the selection of the following support structures.(2)Based on the on-site monitoring of the excavation and deep excavation of the deep excavation section of the exit tunnel of the Aimin Tunnel of Ha-Mu-Ke special project,and combining the geological conditions,hydrological conditions,and surrounding environmental conditions of the foundation pit,the on-site monitoring data were collated and analyzed.The law of internal force and deformation of supporting structure during excavation of the foundation pit.Analysis of on-site monitoring data found that although the internal forces and deformations of the support structure did not exceed the alarm value but were close to the alarm value,it was considered necessary to conduct an optimization design study on the pit from the aspects of economy and safety.(3)By studying the principle of optimization of the supporting structure scheme,an optimization method suitable for this project is selected,namely the AHP,and the original design support scheme is optimized.Two optimized design schemes are proposed: 1)grading excavation + underground continuous wall plus an internal support structure(Optimum plan 1);2)non-grading excavation + underground continuous wall plus two internal support structures(Optimum plan 2).(4)Through the finite element calculation software ABAQUS,the original design scheme,the optimized scheme one and the optimized scheme two were simulated and analyzed.Firstly,the supporting structure of the original design scheme was simulated,the internal force and deformation of the supporting structure were obtained,and the numerical simulation results were compared with the actual field measurement results to verify the correctness and rationality of the model;The first one and the second one are used for numerical simulation,and the results of the optimization with the original design are compared and analyzed.Finally,the comprehensiveness of the safety,economy,construction period,construction difficulty,and environmental impact of the support structure is analyzed through the AHP.Judging,the optimal solution is optimized as the first option,namely slope excavation + underground continuous wall plus an internal support structure.The research results can provide suggestions and references for the support of similar long and deep foundation pit projects.