The installation of mandrel-driven prefabricated vertical drains and resulting disturbance of soft saturated clays are analyzed with a new elliptical cavity expansion theory. This formulated theory accounts for a concentric progression of elliptical cavities in an undrained condition and the large-strain effects in the plastic zone incorporating the modified Cam clay parameters. The total and effective stresses and excess pore water pressure in the soils surrounding the mandrel are predicted taking into account the mandrel installation rate, mandrel dimensions and the time factor. The theoretical variation of excess pore pressure is then compared with the results of large-scale consolidometer tests, which show that the estimated and measured pore pressures are almost the same. The plastic shear strain normalized by the rigidity index is then used to identify the zone of disturbance around the vertical drains. This formulation has been applied to a case history from the Muar clay region in Malaysia, and the results verify the usefulness of the method for determining the extent of the smear zone.
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