Full-vacuum forced-drainage for deep marine soft ground improvement

The effectiveness of traditional vacuum preloading (TVP) for improving deep marine soft ground is fundamentally constrained by vacuum attenuation with depth and well resistance. To overcome these technical barriers, this study introduces a novel full-vacuum forced-drainage (FVFD) method, utilising an in situ vacuum generator positioned at the base of the drainage system. This design establishes an inverted vacuum profile that synergises with maximum hydrostatic pressure at depth, creating a superior hydraulic gradient for pore water expulsion. A rigorous analytical solution for consolidation was derived and verified against field monitoring data. A comparative case study demonstrated superior performance: the final settlement achieved by FVFD was 1.63 times that of TVP (0.65 m vs. 0.40 m), while the construction duration was reduced by over 60%. The findings reveal that FVFD effectively breaks the 10 m depth limitation of conventional surface-source systems, inducing significantly greater pore water pressure dissipation in deep layers. Although direct costs are 16.2% higher, the substantial reduction in project duration offers significant advantages in construction efficiency. This research establishes a highly efficient and proven strategy for deep soft ground improvement across diverse coastal and geotechnical infrastructure projects.