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Prefabricated vertical drains (PVDs) consist of a drainage core encapsulated by a geotextile which serves both as a filter and separator. They are typically 100 mm (4.0 in.) wide by 10 mm (3/8 in.) thick and are on spools of up to 300 m (1000 ft.) in length. They are used to rapidly consolidate saturated fine grained foundation soils. At this time, they have completely replaced sand drains for such purposes. Most ground modification contractors are fully aware of the technology. The presentation will begin with calculating the installation stresses during various parts of the procedure. The geotechnical design process insofar as calculating the time for 90% consolidation will be presented transitioning from Terzaghi to Barron to Hansbo methods. This is followed by four issues, which are somewhat tenuous and remain to be clarified.

Lastly, a completely new issue of recognizing that PVD’s will reinforce foundation soils by virtue of their intrinsic tensile strength is presented. This is illustrated in the context of a major failure which used sand drains. While the increase in FS-value is quite small, there are options presented to enhance the value.

PDHs will be awarded upon completion of a course evaluation form provided by DVGI.