Centrifugal modeling of a composite foundation combined with soil-cement columns and prefabricated vertical drains

A new soft ground improvement method is proposed combined with soil-cement columns and prefabricated vertical drains (PVDs) to increase the bearing capacity and to accelerate the consolidation process of soft soil. A series of centrifugal modeling tests is conducted on an embankment on a composite foundation, combined with soil-cement columns and PVDs. The effects of column spacing and column length on the behavior of the composite foundation are considered. For comparison, two centrifugal modeling tests are conducted on the embankment, one involving only soil-cement columns and the other involving only PVDs. The embankment loads are applied in four stages using a hydraulic jack mounted on top of a strongbox. Scaled-down model columns and a kind of wool strings are used to simulate the prototype soil-cement columns and PVDs, respectively. The load sharing ratio, defined as the proportion of external loads carried by the columns, is used to evaluate the load transfer between the columns and the surrounding soil. The test results indicate that the load sharing ratio increases with an increase in column length and a decrease in column spacing. The ground settlement and the lateral displacement decrease with an increase in column length and a decrease in column spacing. Finally, the use of the combined method to mitigate differential settlements at a bridge approach is discussed.