Research On The Deformation Law And Optimal Design Of The Deep Foundation Pit Support Structure In The Silt Soft Soil Area Of Hangzhou

Traffic congestion has become a phenomenon that cannot be ignored,and a series of chain problems such as environmental pollution and land destruction have appeared with the economic growth of our country since the 21 st century.In order to solve these problems,the development and utilization of underground space has been valued by the engineering community.The adoption of underground excavation pipeline technology can not only solve the traffic problems,but also protect the ground environment,which is of great significance to the sustainable development of society and economy.It is often accompanied by the emergence of a large number of deep foundation pit projects in the process of underground pipeline excavation.Therefore,controlling the deformation of the surrounding structure of the deep foundation pit and the settlement of the surrounding surface are important factors for the safety and stability of construction.A lot of analysis have been made on deep foundation pit by researchers at home and abroad.However,a specific analysis should be made for the deep foundation pit as the geographical location of the actual project is different.In this paper,the finite element numerical simulation and project data analysis of the deep foundation pit excavation process of a shield tunnel were carried out,and the deformation behavior of the deep foundation pit supporting structure of the silty soft soil was deeply studied based on the statistical analysis of the case of deep foundation pit engineering in Hangzhou.Then the optimization analysis of the deep foundation pit supporting structure was conducted based on numerical simulation.The research contents and conclusions are as follows:(1)The deformation characteristics of the retaining structure supported by the deep foundation pits with continuous walls are summarized on the basis of a summary analysis of the data of 10 deep foundation pits supported by underground continuous walls in Hangzhou.The variation range,average value and maximum value position of the maximum ground settlement around the deep foundation pit and the maximum lateral displacement of the underground continuous wall are obtained.Detailed information of the envelope structure,such as insertion ratio,stiffness of supporting system and length-to-width ratio of foundation pit are obtained at the same time.Its influence on the deformation of the retaining structure of the deep foundation pit are analyzed,the distribution law of the maximum deformation of the foundation pit and the relationship between the maximum lateral displacement of the continuous wall and the maximum surface settlement outside the foundation pit are summarized after its influence on the deformation of the retaining structure of the deep foundation pit are analyzed.(2)The deformation law of deep foundation pits is summarized through the analysis of the monitoring data of deep foundation pits: the horizontal displacement and vertical displacement of the top wall of the foundation pit are continuously increasing with the increase of the excavation depth;The ground-connected wall generally exhibits a deformation rule of "medium convex",and the position of maximum lateral movement gradually moves down to the middle of the wall.The maximum lateral displacement of the ground connection wall is 35 mm,and the maximum value is located at 0.7 times the depth of the excavation of the underground pit after excavation of the deep foundation pit is completed.The maximum settlement value of the surface around the deep foundation pit is between 4 and 24 m from the edge of the foundation pit,and the maximum settlement value is-87.3 mm.The surface settlement around the foundation pit is distributed in a "groove" shape.(3)The MIDAS/GTS software was used to perform numerical calculation and analysis on the excavation and support of the deep foundation pit.Then,the ground settlement and deformation of the connecting wall around the foundation pit under different working conditions were studied,and subsequently the simulation results and monitoring results were compared and analyzed.The following conclusions can bedrawn: The simulated value of the ground settlement is smaller than the measured value,and the lateral displacement value of the ground connection wall is closer to the measured value,which initially verifies the feasibility of the model for excavation,and then extract a large amount of data from the model to further analyze the deformation law of deep foundation pits in soft soil area.(4)The MIDAS/GTS software was used to simulate the effect of the steel support servo system on the horizontal displacement of the ground wall of the deep foundation pit and the surface settlement around the foundation pit in the soft soil area,as well as the wall thickness,the number of support channels,and the embedded depth of the ground wall.Then the effectiveness of the steel support servo system in deep foundation pits on soft soil was obtained.The deformation of the surrounding structure of the deep foundation pit and the settlement of the surrounding soil can be reduced by increasing the number of supporting channels,wall thickness,embedded depth and other measures.This paper puts forward optimization suggestions for the retaining structure of deep foundation pits in the soft soil area of Hangzhou,and provides references for similar deep foundation pit projects.