Back-analyses of flow parameters of PVD improved soft Bangkok clay with and without vacuum preloading from settlement data and numerical simulations

Prefabricated vertical drains (PVDs) with embankment preloading (conventional PVDs) and with embankment combined with vacuum preloading (Vacuum-PVDs) are examined using the field data obtained from the site of the Suvarnabhumi Airport, Thailand. The flow parameters were back-analyzed by comparison of measured and predicted or simulated data. The flow parameters were illustrated in terms of the horizontal coefficient of consolidation (Ch) and the ratio between the horizontal hydraulic conductivity in undisturbed zone (kh) and the horizontal hydraulic conductivity in smear zone (ks) or (kh/ks). Numerical simulations using one-dimensional FEM PVDCON software with equivalent vertical permeability, kev, to determine the appropriate Ch and kh/ks of PVDs with conventional embankment preloading and with embankment combined with vacuum preloading schemes were made. Furthermore, numerical simulations using axisymmetric FEM by ABAQUS software, incorporating horizontal (kh) and vertical (kv) permeabilities, to determine the appropriate kh/ks based on back-calculated Ch of conventional PVD and Vacuum-PVD schemes were also done. The Vacuum-PVD scheme indicated faster rate of settlement than conventional PVD scheme by about 1.7-1.8 times with slight reduction of the kh/ks ratios. For conventional PVD, it was demonstrated that the increase in kh/ks ratios reduced the simulated rate of settlement.