The PFC Numerical Simulation Of Vacuum Preloading In Improving Reclamation Sludge

Reclamation silt is typical owed consolidation soft soil formed by hydraulic fill. It shows low strength, high compressibility and low permeability, so soft soils must be reinforced before people build expressway, port and dock etc on them. Vacuum preloading method is effective to improve the soft soil foundation. In Vacuum preloading process, the consolidation settlement rules of reclamation silt foundation are different from that of the general soft soil. Due to particle skeleton is not form, there is a large range of particle flow in vacuum preloading process. Only in the area around the drainage plate (0.2-0.3 meters) the soil strength is more growth and formed the relative permeability and weak close-grained "soil column". But in the area far from drainage plate, the soil compaction degree and strength are constant. Adding vacuum time cannot change this situation. In addition, consolidation deformation of this soil is a big deformation problem. In the process of consolidation, the permeability coefficient and compression coefficient is not constant but with porosity ratio change significantly. The theory and method based on the original hypothesis of small deformation and constant coefficient are no longer applicable. The new theory involving solid deformation and particle flow problem urgently need to be researched.PFC2D,which is based on DEM, abandons the macroscopic continuity hypothesis of traditional continuum mechanics, analyses reciprocity and relative movement between particle and particle, as well as between particle and water from microscopic side:the movement of water complies with continuum function and N-S function; interaction force between particle and water is added to particle as external body force, the movement of particle complies with classical mechanics law, without coupling with displacement continuity and compatibility of deformation. Therefore, PFC2D is suit for simulating drainage preloading course of soft clay ground, and the computing velocity is high.This paper takes with the aid of PFC2D, we established a sand box model. From the model simulation, we study the course of 2-dimensional sand drain ground in ideal situations. We found that soil particles break away from the soil skeleton gradually at the mechanical effect of water infiltration. In this process because of the loss of particles, particles will rearrange, deposition, and inevitably lead to the changes of soil micro structure and mechanical properties, such as the inhomogeneous changes of soil porosity, permeability, internal pore pressure and so on. This simulating method can be used for reference for correlative research.In addition, by changing the model parameters, we go further to study the factors that influence the soil porosity in the different conditions, such as the space of vertical drainage channel, vacuum drainage and the original porosity of the soil. We have established the theoretical model of changes of soil porosity, we have also proposed the construction method improving the efficiency of the drainage preloading and without changing the cost (changing the space of the drainage channels) by in twice lying the drainage boards. So it was of theoretical significance to the further application and development of Vacuum preloading method.