The Research Of Design And Monitor For Retaining Structure Of Tunnel Foundation Pit In Urban Complex Environment

With the rapid advancement of urbanization,multi-level development has occurred in comprehensive urban expansion,and the intensity and speed of underground space development have gradually accelerated.In recent years,a large number of large open excavation foundation pits of tunnel projects have appeared,and such foundation pits are usually high risk,wide influence,high cost for structural support.At present,it was significant to explore one type of pit,which was safe,reliable,efficient and economical,environmentally friendly.To this end,based on the open-cut foundation pit project of the Wangjiang Tunnel of Hangzhou,the following works have been carried out.1.Based on comparative analysis of the characteristics and advantages and disadvantages of various supporting enclosures types suitable for large open-cut tunnel foundation pits,combined with the situation of important protection facilities such as geology,water level and surrounding buildings,rail transit,pipelines,etc.of the Wangjiang tunnel,this dissertation designs the protection scheme of the open-cut section of Wangjiang Tunnel and proposes the scheme of combining the diaphragm wall and the TRD construction method of pile.By using the Qimingxing software,the key parameters of the diaphragm wall and the TRD construction method of pile are calculated and optimized.2.Based on the chosen protection scheme,three-dimensional analysis was carried out for the excavation structure of the TRD method of pile and the underground continuous wall used in the section of Wangjiang Tunnel by Plaxis 3D finite element software.It was compared with the two-dimensional calculation results by the Qimingxing software during the optimized procedure.The comprehensive analysis of the foundation pit enclosure deformation and stress characteristics,which contained lateral deformation,ground settlement outside the pit,and supporting shaft force etc.,had verified the feasibility of the project design ideas and the rationality of the determination of key parameters.3.Through the monitoring and analysis of the deep horizontal displacement of the soil,the surface settlement outside the pit,groundwater level,the supporting axial force,and the settlement of the surrounding buildings during the open-cut foundation pit of the Wangjiang Tunnel,the calculation results in the design process were verified reliability.At the same time,the characteristics of space-time effect of diaphragm wall and TRD construction method of pile were revealed during the analysis of the monitoring data.The successful experience of the foundation pit enclosure design of this project and the research in this paper had a certain practical value,which can provide a reference for the design and monitoring of the foundation pit enclosure structure of similar large-span and open-cut tunnels.