Analysis Of Deformation And Spatial Effect Of Irregular Deep Foundation Pit

Deep excavation is a complex three-dimensional space system,and excavation process is often accompanied by obvious spatial effects.The traditional two-dimensional plane strain calculation method is only applicable to the middle area that is not affected by space effects when the side wall of the foundation pit is long.It cannot accurately calculate the corner area affected by space effects,especially for the complex support structure and geometric plane shape.The calculation theory of complex foundation pits is flawed,so it is necessary to analyze the deformation laws of foundation pits from a three-dimensional angle.Taking an irregular deep foundation pit in Wuhan as an example,this thesis conducted a theoretical study of the spatial effect of the foundation pit,the deformation and space effects of the irregular deep foundation pit during excavation were analyzed and a reasonable deep foundation pit deformation control technology was proposed based on the influencing factors of foundation pit deformation using the three-dimensional finite element numerical simulation with actual engineering monitoring data.The main research results were as follows:(1)According to the influence scope of the internal and external angle effect of the foundation pit,the irregular deep foundation pit was classified.Referring to the concept of plane stress ratio and the calculation method of the influence coefficient of the angle effect of the pit,the calculation method of the spatial distribution considering the influence coefficient of the internal and external angle of the pit was put forward.(2)Combined with the actual monitoring data and numerical simulation results of Wuhan Greenland Fragrant Tree Flower City,the three aspects of horizontal displacement of the top of the pile,ground settlement behind the wall and settlement of surrounding buildings were compared and analyzed.The effects of the deep foundation pit geometry and the support system on the excavation process were studied.The results showed that influenced by the spatial effect of the foundation pit,the displacement at the positive angle was the largest,followed by the displacement at the middle,and the displacement at the negative is the smallest.(3)The sphere of influence of the negative angle effects and the positive angle effects in deep foundation pits were studied by an optimized numerical model.The negative angle effects range of the foundation pit was generally 1 ～ 2 times that of the depth of the excavation,and the positive angle effects range is 2 ～ 3 times that of the excavation depth.In addition,the harms caused by the positive angle effects were effectively suppressed when the influence range of the negative angle effects and the positive angle effects at the continuous positive corners of the irregular deep foundation pit completely overlapped because the soil structure at the negative corners intersected each other,which increased the support strength.(4)The influence factors of deep foundation pit deformation under spatial effects were studied by changing the support method,excavation order and pile row anchor parameters of the foundation pit,and exploring the different parameters for the irregular deep foundation pit retaining structure based on the three-dimensional finite element numerical model.The effective measures to control the deformation of the foundation pit were proposed to guide the economic and reasonable construction principles of irregular deep foundation pits on the premise of ensuring safety.