Analytical Solution Of Consolidation And Numerical Analysis Of Vacuum Preloading Vertical Drain

Soft soil foundation has the characteristics of low strength,large void ratio and high water content,so it needs to be strengthened before it can be used in engineering construction.Drainage consolidation method is a common measure to treat soft soil foundation,and vacuum preloading method is one of the commonly used drainage consolidation methods.After decades of research,the application and theoretical research of vacuum preloading vertical drain consolidation in engineering have been greatly developed and abundant achievements have been achieved,but the analytical results obtained by simplified research are still different from the actual engineering situation.In order to promote the development of the theory of vertical drain consolidation,based on previous research results,this paper studies the problem of vertical drain consolidation under vacuum preloading.The main contents and results are as follows:(1)Aiming at the consolidation problem of vertical drain under vacuum preloading,considering the change of well resistance with time and neglecting the vertical seepage of soil,the calculation model is established.The boundary conditions,initial conditions and continuous conditions are reasonably determined,and the analytical solution is used to conduct theoretical research,and the analytical solution of consolidation by vertical drain considering well resistance change with time under vacuum preloading is derived.Based on this solution,a calculation program is compiled and the consolidation behavior of foundation is analyzed.The research show that the well resistance change rate have great effect on the average pore pressure and average consolidation degree,the well diameter ratio on the degree of consolidation has certain effect but not obvious,and ratio of radial permeability coefficient of the undisturbed soil and disturbed soil on the degree of consolidation is obvious.The greater the vacuum degree is,the slower the dissipation rate of pore pressure with depth is.(2)Under vacuum preloading condition,considering the variation of permeability coefficient in smear area and well resistance with time,and according to the variation law of permeability coefficient.The analytical solution of vertical drain consolidation is given,the calculation program is compiled,and the consolidation behavior of vertical drain is analyzed.The results show that the change rate of well resistance has a great influence on the average consolidation degree,in the three models studied in this paper,mode three is the fastest consolidation,model two second,model one consolidation slowest.(3)The consolidation problem of vacuum preloading vertical drain considering the non-linear of soil in the affected area is studied.The analytical solution of consolidation of vertical drain considering the nonlinearity of soil,the change of radial permeability coefficient and the change of load with time is derived.The calculation program is compiled and the consolidation behavior of vertical drain under instantaneous and linear loading modes is analyzed.The results show that the vertical drain pore pressure dissipation rate under linear loading is slower than the instantaneous loading.The consolidation rate increases with the increase of permeability coefficient of drainage.The greater the ratio of the compressibility index to the permeability index,the slower the consolidation rate of the foundation.(4)Based on the circular equivalent principle of plastic drainage plate,considering the variation of soil radial permeability coefficient in smear area and vacuum preloading.The general consolidation solution of vertical drain with arbitrary load varying with time is derived by analytic method.On the basis of the general solution,the closed solution under instantaneous load and linear load is further given.The calculation program is compiled and the consolidation curve of vacuum preloading vertical drain based on circular equivalent is drawn.The results show that the equivalent annular consolidation rate is less than that given by the equivalent circumference.With the increase of the area reduction coefficient,the consolidation rate of the equivalent annular approaches to the consolidation rate of the equivalent circumference.With the decrease of the permeability coefficient of the vertical drain,the influence of the permeability coefficient on the consolidation rate is weakened.The dissipation rate of pore water under instantaneous load is greater than that of linear pore water dissipation.The dissipation rate of pore water under instantaneous load is greater than that of linear pore water dissipation.(5)The general finite element software ABAQUS is used to carry out numerical analysis of vertical drain under vacuum preloading.The results show that the numerical simulation results are in good agreement with the analytical solutions,and the vacuum transfer in the vertical drain is in accordance with the actual situation.Comparing the results of elastic model and elastic-plastic model,it is found that the elastic model overestimates the consolidation rate of foundation soil.