Design curves for prefabricated vertical drains

Vertical drains and preloading are very effective and economical ground modification techniques for accelerating primary consolidation and compensating some secondary compression of soft compressible soils. If vertical sand drains are used, they can be installed at different diameters. The drain diameter required thus becomes a dependent variable in the design process and the drain spacing is determined a priori. The required parameters can be obtained after a few iterations. However, the number of iterations may increase significantly when prefabricated vertical drains or strip drains are used as the drain size is predetermined by manufacturers and available only in a very limited range. Design curves are developed for prefabricated vertical drains in this paper. The equivalent drain diameter is used as the independent variable and drain spacing becomes the dependent variable. Soil smear around the drain is considered but well resistance of the drain is neglected. The curves can be used to design a vertical drain system without unnecessary iterations and/or interpolations when the equivalent drain diameter, degree of consolidation required, time available, and pertinent geotechnical engineering properties of the soil to be consolidated are given.