Numerical modelling of prefabricated vertical drains and surcharge on reinforced floating column-supported embankment behaviour

The short-term and long-term performance of reinforced, deep mixing method (DMM) floating-column supported embankments with and without prefabricated vertical drains (PVDs) are investigated using a fully 3D coupled model. The concurrent use of PVDs with the other two forms of soft ground improvement significantly shortens time for subsoil consolidation and also substantially reduces post-consolidation lateral displacements and post-construction crest settlements. The combined use of PVDs and surcharge preloading to meet a requirement of 100 mm post-construction crest settlement for a bridge approach embankment is examined. Compared to a comparable case with surcharge preloading but without PVDs, the synergistic effects of PVDs and 0.5 m fill surcharge preloading diminish the calculated post-construction crest settlement from 0.228 m to 0.036 m and reduce the post-consolidation horizontal movement below the toe at the ground surface level from 0.115 m to 0.067 m even though embankment is constructed 5 times faster in the case with PVDs.