Evaluation of four equivalent diameter formulations for prefabricated vertical drains using flow rates

The rectangular cross-section of a prefabricated vertical drain (PVD) is typically converted to a circular cross-section to aid in design. This conversion is performed regardless of whether the PVD will be used for soil improvement or for remediation. An experimental programme to evaluate four of the most commonly used equivalent diameter formulations based on flow rates is described, and the results from those experiments are presented. The results indicate that the formulation recommended by Hansbo in 1979 adequately simulates a PVD under both injection and extraction conditions. Furthermore, there was no dramatic difference observed for the flow rates from, or into, a PVD with and without smear. It should be noted, however, that the tested material was a silty sand, and hence the effect of smear should not be significant.