Three-Dimensional Nonlinear Numerical Analysis of Consolidation of Soft Ground Improved by Sand Columns under a Freeway Embankment in Shallow Sea: Case Study

The freeway embankment linking Meizhou Island with Putian City in Fujian, China, passes through a shallow-sea area. Sand columns distributed in regular triangles and sand cushions reinforced with geogrids were employed to accelerate the consolidation of the soft ground beneath the embankment and improve its bearing capacity. In this study, three-dimensional (3D) finite-element analysis was carried out using the modified Cam-clay model to enhance the level of design and analysis of this complicated practical engineering problem of soft-ground improvement in terms of accurate prediction of the settlement, horizontal displacement, period of surcharge preloading, and variation of excess pore-water pressure. The predicted settlement and horizontal displacement of the embankment subgrade were found to agree well with the actual measurements. In line with the prediction of a consolidation degree of 95%, ultimately, the 340th day was determined to be the optimal date on which to remove the surcharge. In addition, the 3D effect of the variation of excess pore-water pressure was clearly revealed. The results prove that the 3D nonlinear numerical method presented in this paper is scientific and reliable for complicated practical engineering problems involving soft-ground improvement