Comparative numerical analysis of ground-improvement techniques for embankment performance on soft soil: insights into rigid, semi-rigid, and drainage-based solutions

This study develops and validates a mechanistically consistent plane-strain finite-element framework to elucidate how stiffness contrast and drainage capacity interact in controlling embankment performance on soft clay. A column-wall formulation is combined with coupled deformation-consolidation analysis and benchmarked against full-scale field data, reproducing settlement and excess pore-pressure responses with deviations generally < 15% during construction and < 10% during consolidation. Under identical geometry, stratigraphy, and staged loading, the results demonstrate that serviceability is governed primarily by stiffness-driven load bypassing rather than drainage efficiency. Rigid and semi-rigid inclusions limit construction-stage settlement to 5.9–6.3 mm, compared with 10.9 mm for prefabricated vertical drains (PVDs) and 15.1 mm for granular columns, corresponding to reductions of approximately 46% and 42% relative to PVDs, and 61% and 58% relative to granular columns, demonstrating their superior short-term deformation-control performance. In contrast, excess pore-pressure response reveals an inherent trade-off: inclusions suppress peak construction-stage pore pressure to 24.6–25.8 kPa (15–19% lower than PVDs at 30.5 kPa) via stress redistribution, yet consolidate slowly (270–300 days), whereas drainage-based systems dissipate pore pressure within 45–55 days at the cost of higher initial buildup. Vertical stress partitioning is shown to be stiffness-controlled, with concrete piles attracting 85–90 kPa peak stress and unloading the soft clay by 40–60%, directly underpinning stability gains; construction-stage FS increases from 1.293 (PVDs) to 2.14–2.15 (65–66%). The findings reframe ground-improvement selection as a performance-based stiffness-drainage interaction problem, providing a quantitative basis for rational and material-efficient embankment design.