Deformation Monitoring And Numerical Simulation Analysis Of Deep Foundation Pit Based On Spatial Effect

In order to alleviate the shortage of urban land demand and realize the efficient use of urban space,more and more large-scale and irregular foundation pit projects begin to appear.The soft soil strata in coastal cities of China are widely distributed and the geological conditions are relatively complex.Under such conditions,it is more necessary to strictly control the deformation of foundation pit to build a deep foundation pit.Taking a deep foundation pit project in Shanghai as an example,the formation mechanism of spatial effect of foundation pit is discussed through theoretical analysis,and the influence range of spatial effect is calculated accordingly.Secondly,the spatial deformation law of foundation pit and surrounding environment is analyzed by means of statistics of monitoring data,and then a three-dimensional numerical model is established to calculate the deformation in the process of foundation pit construction,and the rationality of the model is verified by comparison with the monitoring data.Then,several pit models with different pit angle are established,and the influence of pit angle on spatial effect is analyzed quantitatively.Finally,the spatial deformation of the foundation pit is analyzed by changing the excavation method and adjusting the support position,and the construction method is optimized,which can provide reference for the deformation control in the foundation pit construction.In view of the determination of the influence scope of the spatial effect of the foundation pit,based on the arch effect of the soil,two forms of the spatial deformation of the foundation pit are obtained by analyzing the relative position of the soil arch and the ideal sliding crack surface;secondly,the calculation formula of the influence scope of the spatial effect is derived by quantifying the geometric parameters of the soil arch and the ideal sliding crack surface;In view of the spatial deformation law of each monitoring item of the foundation pit,the monitoring data of the deformation of the retaining structure of the foundation pit,the settlement of the surrounding surface,the uplift of the pit bottom,the deformation of the pipeline and the axial force of the support are analyzed comprehensively.The results show that the axial force of the angle brace is obviously smaller than that of the opposite brace,the maximum horizontal displacement of the retaining structure appears near the excavation surface of the foundation pit,the surface settlement presents two trends of triangle and parabola along the direction away from the foundation pit,there is a relationship between the pipeline settlement and the soil settlement,and the revised soil settlement calculation formula can predict the pipeline settlement.In view of the influence degree of pit angle on the spatial effect of foundation pit,the influence coefficient of spatial effect is defined,and the numerical calculation model of pit angle of 45°?150°is established to calculate the horizontal displacement of retaining structure with a gradient of 15°.The results show that the larger the angle of foundation pit is,the less obvious the spatial effect is.In view of the problem of deformation control in the process of foundation pit construction,a numerical model is established to calculate the deformation of foundation pit under three kinds of excavation and three kinds of support modes.The results show that the method of excavation from east to West in layers and backward excavation is selected,and the excavation of a wider side of foundation pit is divided into two parts of North and south,and the maximum surface settlement and horizontal displacement are obviously reduced.There is no great fluctuation in the deformation of foundation pit after the lm is moved up and down.If the construction needs,it can be adjusted appropriately.