Measured Performance and Analysis of the Residual Settlement of a PVD-Improved Marine Soft Ground

Prefabricated vertical drains(PVDs)are commonly used to shorten the drainage path for consolidation as part of the improvement of marine soft ground.Many studies that focus on the primary consolidation settlement of PVD-improved soft ground have been conducted;however,residual settlement has been scarcely investigated.Residual settlement is the net effect of secondary compression and the remaining primary consolidation and generally occurs while the facilities are operating.In this study,residual settlement was investigated using the measured field settlement data obtained from the surface settlement plate and multilayer settlement gauges.This study determined that PVD still has some effect on residual settlement and can reduce the settlement times.Residual settlement is only related to the PVD-improved soil layer and only occurs significantly in the middle zone of that layer over a few months.The middle zone may be related to the time delay of excess pore water pressure dissipation.This study concluded that the remaining primary consolidation in the PVD-improved soil layer is the primary cause of residual settlement,whereas secondary compression in the PVD-improved soil layer is only a minor cause.