Densification of loosely deposited soft soils using the combined consolidation method

•The combined consolidation method (CC) was applied at a site with soft soils.•CC integrates low-energy DC and vacuum dewatering.•Field tests were conducted to determine the factors that influence CC.•Field studies included deformation, CPT, SASW and plate loading tests.•After CC, the improvement depth at the site was at least 6 m.

Dynamic consolidation (DC) has been widely used for a variety of soil types and conditions, particularly for soft soils, due to its superior results and low cost. However, soft soils become ‘rubbery soils’ when the groundwater table is high and the single DC method is used. In this paper, the combined consolidation (CC) method was applied to a site with loosely deposited soft soils in the Yangtze River Delta of China. This method integrates two technical construction characteristics, low-energy DC and vacuum dewatering. To properly manage these soil conditions and optimize the CC design, field tests were conducted to determine the factors that influence CC. Deformation tests that consider ground settlement, pore water pressure, and the groundwater table were performed to obtain rational construction parameters and to provide proof regarding the adjustment of the original CC procedure. Drilling sampling and cone penetration, surface wave, and plate loading tests were conducted to evaluate the overall effects of CC. The allowable bearing capacity and the depth of improvement at the site were estimated to exceed 120 kPa and 6 m, respectively. Both of these values meet the design requirements.