| Vacuum preloading consolidation method is one of the methods widely used to reinforce large area soft soil foundation,which has the advantages of large consolidation settlement and simple construction technology.During the consolidation process,the compressibility and permeability of soft soil change all the time,and there are significant differences in spatial distribution.It is rare that the existing literature considers the influence of deformation nonlinearity and permeability evolution nonlinearity of soft soil at the same time.This study analyzes and summarizes the nonlinear characteristics and calculation formulas of deformation modulus and permeability coefficient of soft soil during consolidation.Based on FLAC3D platform,the vacuum preloading drainage boundary is treated as the absolute pressure leakage boundary,and a FISH program which can reflect the nonlinear characteristics of deformation and permeability evolution simultaneously is developed.The rationality of the method is verified by laboratory test results.The influence of vacuum degree under film,evolution equation of soil permeability coefficient and leakage boundary on consolidation characteristics of soil foundation are also studied.Based on the data of the experimental area of Tianmu River channel vacuum preloading regulation project,a numerical model of vacuum preloading was established to analyze the nonlinear consolidation effect in the experimental area.The main research results are as follows:(1)In the numerical method of vacuum preloading consolidation,it is feasible to use the absolute pressure leakage boundary and the nonlinear relationship between permeability coefficient and deformation modulus to reflect the settlement deformation of nonlinear consolidation of soft soil.The numerical results of settlement and vacuum degree of nonlinear consolidation of soft soil are close to those of laboratory test,and the relative error is less than 8%,so the nonlinear consolidation model of vacuum preloading of soft soil is reasonable.(2)At the end of vacuum preloading,the vacuum degree and deformation modulus near the drainage plate and the soil surface layer are large,and the permeability coefficient is small,but the vacuum degree far away from the drainage plate and the soil depth is small,which indicates that the consolidation effect near the drainage plate and the soil surface is good.In the process of vacuum preloading consolidation,the nonlinear deformation and permeability evolution of soil are the main reasons for the rapid settlement of soft soil at the initial stage and the slow settlement at the later stage.(3)The vacuum consolidation effect can be effectively improved by increasing the vacuum degree under the film,but the higher the vacuum degree is not the better.If the vacuum degree under the film is greater than 80 kPa,the consolidation speed will be slowed down.Comparing the calculation re sults of different permeability numerical models,it is found that the semi-logarithmic function relationship between void ratio and permeability coefficient has the advantages of simple form and good consolidation effect of vacuum preloading,which is the optimal nonlinear permeability relationship.Comparing the calculation results of different leakage boundaries,the consolidation effect of absolute pressure leakage boundary is better.(4)The vacuum preloading nonlinear consolidation model can effectively simulate the experimental area of Tianmu River channel vacuum preloading regulation project.The variation law of that calculate value is basically consistent with the measured value.The pore water pressure in the foundation is linearly distributed before and after calculation.The negative pressure transmission depth of the foundation in the experimental section is about 5m.The consolidation effect of the shallow soil under vacuum preloading is good,and the consolidation effect at the early stage of vacuumizing is good.This change rule is directly related to the nonlinear changes of soil compressibility and permeability.Vacuum preloading makes the reinforced area appear larger horizontal displacement,and the consolidation settlement of vacuum preloading is mainly composed of the compressive consolidation amount of easily compressible silt layer.(5)The changes of consolidation settlement,deformation modulus and permeability coefficient in the foundation soil layer are synchronous.The vacuum preloading will first change the consolidation characteristics of the shallow soil layer,and then affect the consolidation of the deep soil layer.The changes of the consolidation characteristics of the soil layer in the early stage of vacuumizing will also affect the consolidation of the soil layer in the later stage.The consolidation characteristics of the soil layer change synchronously along the depth direction and also change synchronously with time. |
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