Stability Analysis of Asymmetric Embankment Widening and Reinforcement on Soft Foundation Using Centrifugal Model Tests and Numerical Simulations

To ensure the safe operation of embankment projects in flood detention areas, this study systematically investigates the rehabilitation and filling works of the embankment on soft foundation in the Fuhua Area of the Huayang River flood detention basin. Given the high natural water content, large void ratio, low permeability, and low bearing capacity of the soft soil, both centrifugal model tests and numerical simulations were employed. The variations in foundation strength, pore water pressure, and embankment settlement were examined under three-stage filling surcharge conditions, comparing the untreated foundation and the foundation treated with prefabricated vertical drains (PVDs) combined with surcharge preloading. The results show that, compared with the untreated foundation, the strength of the soft soil increases markedly after PVD plus surcharge preloading treatment. With increasing surcharge height, both the calculated and measured soil strengths increase with depth. Under the same surcharge preloading stabilization condition, the calculated values are greater than the measured ones at shallower depths, whereas the measured values exceed the calculated ones at greater depths, indicating that the theoretical calculations are conservative. Pore water pressure gradually rises with soil depth, yet the excess pore pressure induced by surcharge dissipates rapidly through PVDs, effectively accelerating the consolidation process. In terms of settlement, the treated soft foundation exhibits larger deformation during the preloading construction stage, which is intentionally induced to accelerate consolidation. This results in significantly smaller post-construction settlement compared with the untreated case, confirming that PVD treatment can effectively reduce long-term settlement. To further verify the reliability of the centrifugal model test results, finite-element numerical simulations were performed on the prototype section, and four settlement monitoring points and six pore-water-pressure monitoring points were selected for analysis. The simulation results show that the pore water pressure along the centreline of the old embankment (the non-drainage consolidation zone) is substantially higher than that under the new embankment (the drainage consolidation zone), demonstrating that PVD treatment can effectively lower pore water pressure and accelerate consolidation. These findings offer important technical support for soft foundation treatment and embankment filling projects.