Research On Spatial Effects Of Deep Slender Foundation Pits Based On Additional Earth Pressures

As the plane dimension of deep slender foundation pits is smaller than the excavation depth,it has obvious spatial effects.The traditional design calculation method fails to consider the effect of spatial effects reasonably,which makes the design result greatly different from the actual situation.In order to further understand the spatial effect characteristics of deep slender foundation pits and to study the internal mechanism of deformation of soil,the spatial effects of deep slender foundation pits and the relationship between earth pressure and displacement on supporting structure were studied by using model test and three-dimensional finite element numerical simulation method.The main work of this paper is as follows:1.This paper summarized the current research results on the spatial effects of deep slender foundation pits,and summarized the manifestation law,calculation method and theory of the spatial effects.Researches in understanding the spatial effects of retaining structures are still in initial qualitative analysis stages.2.The laboratory model test was carried out to study the spatial effect of deep foundation pit.The author designed and made test model and measure the displacement,bending moment and soil pressure of the supporting structure.The soil pressure,displacement and bending moment of the supporting structure during the excavation of deep cylindrical foundation pit with or without loads of different sizes were studied.3.The three-dimensional finite element model of deep foundation pit was carried out.The distribution law of displacement and earth pressure of deep cylindrical foundation pit supporting structure was deeply analyzed.The relationship between deformation of supporting structure and actual earth pressure and additional earth pressure was studied through model test and numerical simulation.4.Three spatial effect ratios including displacement ratio,earth pressure ratio and bending moment ratio of a retaining structure were defined for the sake of analyzing the spatial effects of retaining structures of hollow slender foundation pits.The spatial effect ratios and the relationships of additional earth pressures vs.wall displacements were obtained from the results of the finite element analyses and model tests,and they all shown significantly variation with the process of excavation,and show a strong tendency in their distribution at different positions.5.Based on the results of laboratory tests and numerical simulation,the characteristics of spatial effects of deep cylindrical foundation pit were summarized.The deformation and stress of the soil around the foundation pit were analyzed.There were soil arching effects in horizontal and vertical planes.Both of them reflected the spatial effects of the soil in three-dimensional space,it was suggested that the soil arching effect be defined as the soil shell effect.