Analytical Solutions for Consolidation of Combined Composite Ground Reinforced by Short Impervious Columns and Long PVDs

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.