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The technology of composite ground has been widely adopted in various engineering projects, and it presents the trend from a single column type to the combined use of multiple types. The combined use of long prefabricated vertical drains (PVDs) and short soil–cement columns (impervious columns) has been proposed and utilized in several ground improvement projects. The research for the consolidation behavior of combined composite ground could facilitate the design and calculation of it in practice. Nevertheless, almost no analytical theories for consolidating such a technique are available in the literature. To fill this gap, an analytical model including multiple long PVDs and short impervious columns is proposed to predict the coupled radial–vertical consolidation of the combined composite ground. The analytical solutions under instantaneously and multistage loading are obtained based on the assumption of equal strain and Darcy's law. The average degree of consolidation calculated by the current study is then compared with several existing analytical models of composite ground. Furthermore, a parametric study is carried out to investigate the impacts of various factors on consolidation behavior. The results show that the increasing penetration ratio of the short impervious columns can accelerate the consolidation rate. Moreover, the distribution patterns of the construction site, the compression modulus ratio of impervious columns and soil, and the well resistance and smear effect of PVDs can also influence the consolidation behavior of the combined composite ground. Finally, the reasonability of the proposed analytical model is verified by comparing it with the measured test data reported in the literature. [ABSTRACT FROM AUTHOR]

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 -lg σ and e -lg k 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, C c / C kv has little influence on the consolidation rate and can be ignored compared with C c / C kh. Furthermore, the increase in the stress increment within the ground due to the external loads leads to an acceleration of the consolidation when C c / C kh(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. [ABSTRACT FROM AUTHOR]