Nonlinear consolidation analysis for composite ground with combined use of impervious columns and prefabricated vertical drains under time-dependent loading

Abstract

The technique of the combined use of soil-cement columns (impervious columns) and prefabricated vertical drains (PVDs) has been proposed and widely utilized in ground improvement projects. However, there are few theoretical investigations on the nonlinear consolidation behavior of this combined technique. To fill this gap, the logarithm models of e-lgσ and e-lgk are incorporated to describe the nonlinear consolidation characteristics of soils. Meanwhile, a mathematical model for the nonlinear consolidation of combined composite ground is established by considering the variation of the column-soil compression modulus ratio with consolidation. The governing equations and simplified analytical solutions for four types of loading schemes are obtained in consideration of the smear effects of both impervious columns and PVDs and the well resistance of PVDs. The calculated results of this paper are then compared with the proposed models and the impacts of various parameters on the nonlinear consolidation performance are investigated. The results show that ignoring the nonlinearity will overestimate the consolidation rate when the soil’s compressive indices are greater than the permeability indices. Besides, Cc/Ckv has little influence on the consolidation rate and can be ignored compared with Cc/Ckh. Furthermore, the increase in the stress increment within the ground due to the external loads leads to an acceleration of the consolidation when Cc/Ckh(v) > 1, and the dissipation rate of the excess pore water pressure increases by a maximum of 15 %. Finally, a field case study is conducted to verify the prediction ability of the current model.