Probabilistic observational method for design of surcharges on vertical drains

Preloading with a surcharge is today commonly used together with prefabricated vertical drains for embankment construction on clayey soil to accelerate primary consolidation and increase strength. Because of considerable uncertainty related mainly to the rate of consolidation, there is a need to account for this in the vertical drain and surcharge design to ensure quality in the embankment construction. Addressing this issue, the paper presents a novel probabilistic design methodology that is compatible with the observational method. The procedure evaluates the suitable surcharge load to be used in combination with a vertical drain design in order to ensure that the established design criteria are satisfied with acceptable probability.