Consolidation analysis of staged-filled soil slurry with combined grid-horizontal and vertical drains system under vacuum preloading

This study presents a combined method utilizing grid-horizontal drains assisted by vacuum preloading for initial treatment, and vertical drains with vacuum preloading for further enhancement, aimed at the beneficial reuse of dredged marine sediments as fill material. A novel method for analyzing the consolidation of staged-filled soft soils with grid-horizontal and vertical drains under vacuum preloading is established, and a numerical model, called Combined-drains Consolidation Settlement (CCS), is developed. CCS accounts for staged filling, drain combinations, creep strains, hydraulic conductivity anisotropy, vertical and radial flows, smear effects, time-dependent surcharge and/or vacuum loading, and variable compressibility and hydraulic conductivity throughout the consolidation process. A large-scale laboratory consolidation test is presented, focusing on staged-filled marine sediments treated by the combined system, demonstrating beneficial reuse potential of high-water-content dredged sediments. Settlement and water content predictions using CCS agree well with experimental results. The effects of paving rate (lateral spacing) and the number of grid-horizontal drain layers (vertical spacing) are evaluated using the CCS model. Based on these results, cost-effective design recommendations are proposed. Comparison of treatment efficiency shows the combined method significantly enhances improvement by enabling earlier application of vacuum consolidation than the PVD-only method.