Performance of PVD improved soft ground using vacuum consolidation methods with and without airtight membrane

In order to investigate the performance behavior of soft ground improvement using different vacuum consolidation methods (VCM) and different PVD thicknesses, four trial sections namely C1, C2, D1, and D2 were constructed. VCM without airtight membrane using cap drains and direct tubing system (VCM-DT) were used for the first two sections with PVD thickness of 3 mm and 7 mm for C1 and C2, respectively. VCM with airtight membrane and band drains (VCM-MB) were applied for the last two sections for D1 and D2with PVD thickness of 3 mm and 7 mm, respectively. The soil conditions, construction procedures, instrumentation program, and monitored results of the above trial sections are presented in this paper. The results confirmed that the effective vacuum pressure in PVD mainly depends on vacuum consolidation methods and the assumption of uniform distribution of vacuum pressures along the PVD depth which can be suggested for practical design. For VCM-MB using PVD thickness of 3 mm arranged in triangular pattern of 0.9 m spacing, the degree of consolidation of more than 90% can be achieved in less than 8 months of vacuum pumping. However, for VCM-DT, further investigation is needed for preventing air leakage in vacuum system particularly for the case of thick soft clay deposits with large deformations during the preloading.