Study On Spatial Effect Analysis And Deformation Control Of A Soft Soil Deep Foundation Pit In Wuhan

With the rapid progress of urbanization in China,the foundation pit engineering toward the growing area,deeper and deeper,the surrounding environment,this trend makes theoretical research,design and construction of deep foundation pit engineering are facing with many problems.Restricted by many factors,foundation pit and it's supporting system in space with irregular shape and the spatial effect will affect the deformation of foundation pit supporting structure and surrounding soil.Due to the rheological characteristics of soft clay,the effect is obvious.The conventional design method of foundation pit using two-dimensional analysis method to select the typical profile analysis cannot reflect the three-dimensional failure characteristics of foundation pit,therefore,for the safe construction of the foundation pit,it must be study further on spatial effect and take corresponding deformation measures.Combining with a soft soil deep foundation pit engineering in Wuhan,the pit-retaining structure is secant pile-anchor retaining,due to the bad soil layer thick soft soil foundation pit,the engineering geological conditions are more complex,belong to the middle complex site.The research contents and results of this paper are as follows:(1)Selecting the modified Mohr-Coulomb soil constitutive model,by using the finite element software Midas/GTS NX to build numerical model of foundation pit.By comparison with the results of numerical simulation and practical monitoring value analysis,in the numerical simulation,the increase of excavation depth of palisade structure at the top of the amount of lateral is the same as the actual monitoring results and verifying the numerical model and calculation parameters are correct and reasonable.(2)Respectively,from the monitoring data and the results of numerical simulation analysis of foundation pit spatial effect,mainly analyzing the change law of the top displacement of retaining structure,land subsidence,deep horizontal displacement,cable force and distribution of bottom ground,it is concluded that the maximum influence lengthof spatial effect is about 22 m from the corner of the foundation pit.The influence depth of the spatial effect in the pit bottom of the foundation pit is deep within the depth of the excavation depth of 1.5 times.The influence depth of the spatial effect of the pit boundary is mainly in the depth range of 0.5 times foundation pit excavation.(3)The influence law of spatial effect in horizontal direction and vertical direction is analyzed further.The influence of horizontal spatial effect and the vertical spatial respectively with distance from the top of the retaining structure and the distance from foundation pit border had a linear relationship,and it is concluded that calculation the projection area of the influence scope of both respectively in retaining structure.(4)Simplified numerical model of foundation pit,the excavation depth of model remained constant,the length and width is a quarter of the actual numerical model.Mainly analyzes the impact of the depth of the retaining wall,the depth of layered excavation,block excavation and other factors on spatial effect of foundation pit,and puts forward corresponding measures to control the deformation of foundation pit.