Large-Strain Nonlinear Consolidation of Sand-Drained Foundations Considering Vacuum Preloading and the Variation in Radial Permeability Coefficient

Abstract

The vacuum preloading method effectively strengthens soft soil foundations with vertical drainage, which produces a smear effect when laying sand drains. Meanwhile, the seepage of pore water and soil deformation during consolidation exhibit nonlinear characteristics. Therefore, based on Gibson’s 1D large-strain consolidation theory, this paper developed a more generalized large-strain radical consolidation model of sand-drained soft foundations under free-strain assumptions. In this system, the double logarithmic compression permeability relationships for soft soils with large-strain properties, the variation in the radical permeability coefficient in the smear zone, and the effect of the non-Darcy flow were all included. Then, the partial differential control equations were numerically solved by the finite difference method and validated with existing radical consolidation test results and derived analytical solutions. Finally, the influences of relevant model parameters on consolidation are discussed. The analysis shows that the greater the maximum dimensionless vacuum negative pressure P0, the faster the consolidation rate of sand-drained foundations. Meanwhile, the decrease in the negative pressure transfer coefficient k1 will result in a decreasing final settlement amount. Moreover, the consolidation rate of sand-drained foundations is slower considering the non-Darcy flow, but the final settlement is unaffected.

Double Drainage Consolidation Theory of Vertical Drains Based on Continuous Drainage Boundary Conditions

“…However, the low permeability of dredged fills makes the developed excess pore water pressure more difficult to dissipate. Vertical drains can introduce radial drainage channels in the soil and decrease the seepage path, so they are often used to accelerate the consolidation of dredged fills [1][2][3]. Research on the consolidation theory of vertical drains has been carried out extensively.…”

“…In 1948, Barron [4] proposed a radial consolidation theory for vertical drain-improved ground for the first time. Since then, many researchers have revised the original theory of Barron [4] in different aspects, such as the introduction of the "equal strain hypothesis" [3,5,6] and the "free strain hypothesis" [7][8][9]. The "equal strain hypothesis" is relatively simple and is suitable for the conditions where the additional load is uniform and the loading area is large enough.…”