Field Test Verification and Consolidation Model of a Sand-Doped Soft Soil Foundation with Vacuum Pressure

Abstract

In this study, a field test on the consolidation of sand-doped improved soft soil under surcharge-vacuum preloading is carried out. By analyzing the vacuum pressure transmission efficiency, the settlement rate, and the dissipation rule of excess pore-water pressure of sand-doped and original soft soil foundation in the consolidation process and comparing the indices of vane shear strength, water content, and void ratio before and after consolidation, the technical superiority and reinforcement effect of the sand mixing method for improving soft soil are comprehensively evaluated. Considering the fact that the vacuum pressure decreases linearly along the depth and the surcharge preloading is applied linearly, an assumption of equal volumetric strain is introduced to reflect the lateral deformation, and an axisymmetric nonlinear radial consolidation model of sand-doped soft soil is established. The model accuracy is verified by model degradation research and a field test. The results show that the sand-doped method (20% sand content) can improve the transmission efficiency of vacuum pressure, reduce the loss of vacuum pressure along the prefabricated vertical drains, accelerate the dissipation rate of excess pore-water pressure, increase the final settlement and shear strength, reduce the final void ratio and water content, and improve the reinforcement effect of deep soil. A nonlinear consolidation solution of the sand-doped soil with linear surcharge preloading considering the actual negative boundary conditions can reflect the consolidation behavior more accurately. If lateral deformation and linear surcharge preloading are not considered, the consolidation rate of soil will be overestimated.