Study On Unloading Mechanical Characteristics Of Marine Soft Soil And Numerical Simulation Of Foundation Pit Excavation

The soft soil is widely distributed in the coastal area,and the stress-strain relationship is affected by the stress level,stress history,stress path and so on.A large number of engineering examples and researches show that the deformation and mechanical properties of soft soil under the condition of loading and unloading are significantly different.In the tunnel engineering,excavation of foundation pit and some other engineerings involved unloading,using the method of conventional load theory or the empirical reduction method,often the actual situation and the calculation results of large error,and even lead to catastrophic accidents.In recent years,many scholars have made some achievements on the effect of unloading stress path on the deformation properties of the soil.But because of the regional characteristics of soft soil is obvious,the existing research results with general area remains to be further studied.This paper based on the example of a deep foundation pit engineering in Shenzhen,using the research methods theoretical analysis,laboratory tests and numerical simulation analysis of soft soil under unloading stress path and the initial pore water pressure on the deformation of foundation pit.The main work are as follows:(1)Unloading shear test on the Shenzhen silt soft soilare conducted by simulating the stress path of foundation pit excavation.Compared with the results of the conventional triaxial experiments,the stress-strain curves,the initial deformation modulus,the pore pressure change curve and the shear strength parameters of soft soil under different stress paths are obtained.(2)The UU0.0 stree path unloading shear teat are conducted based on initial pore water pressure,and deformation curve and shear strength curves of soft soil are obtained.(3)Considering the influence of the unloading stress path and the initial pore water pressure,the empirical formula of tangent deformation modulus is proposed based on the Duncan-Chang model.(4)Based on the example of a deep foundation pit engineering in Shenzhen,the BP neural network model is established according to the monitoring data of the lateral deformation of the underground continuous wall,and soil parameters are obtained by inversion.FLAC3 D software is used to simulater the excavation of foundation pit.Comparing the differences between inversion parameters and test parameters of each groups.