Strengthening Characteristics Of Vacuum Preloading And Numerical Simulation

Based on former research and plentiful experimental data, the change laws of underground water level, vacuum degree and pore-water pressure are deeply researched by theoretically analyzing and numerically calculating. The main works in this paper are listed as follow:Firstly, the data measured from field test and vane shear test and static cone penetration test of vacuum preloading were summarized. The analysis result was showed that treating soft clay ground with vacuum preloading was very efficient.Then consolidation characteristic and distortion law in soft soil under negative action were studied in this paper. On the basis of field test, the vertical and lateral deformation characteristics of the foundation in the area of vacuum preloading, the changes of cavity pressure, water level and vacuum degree in different depths, the changes of the subsoil characteristics before and after preloading, are comprehensively discussed. And through the initial analysis of the mutuality between the vacuum power in unit area, and the subside rate, the groundwater table and the vacuum degree in PVD/sand, certain relationship will be found between the vacuum time needed to reach the criterion and the vacuum power working in unit area (or the working number of vacuum pump) is pointed out. Through the comprehensive research of the changing condition of the streams in the water tank of the draw vacuum system and the experimental materials in the construction site, it can be suggested that the streams are discontinuous in sand well, and the vacuum degree in sand well diminishes with depths like stairs in the course of draw vacuum, the diminishing is slower with time, and the stairs are more and more unobvious, which will change almost as a line. Then the theory can be used to analyze the vacuum surcharge preloading depths and characteristics.The relative stable seepage velocity field can be produced with the pumping time. The depth of negative pore-water pressure transferring increases with the PVDs' length. The negative pore-water pressure influence depth can reach 4～6m below the PVDs in the silt when the well resistance is small. According to the reinforcement mechanism of vacuum preloading, the reasons of the change time of pore-water pressure lagging behind loading time are analyzed.Finally, on the basis of Biot's Consolidation Theory, the real engineering was simulated and analyzed with ABAQUS, a general purpose finite element program. The Mohr-coulomb plasticity model was used to simulate the soil consolidation process under vacuum preloading, Further more, the deformation influence of the factors under vacuum preloading was studied, such as degree of vacuum, driving space between plastic drain plates, depth of plastic drain plates and coefficient of consolidation, etc. as the result, the value of vertical displacement and horizontal...