When the anticipated time for consolidation exceeds the allowable construction schedule, vertical drains are installed to accelerate the rate of consolidation. Vertical drains provide an artificial drainage path for the water flow. It consists of a central core, whose function is to act as a free draining channel enclosed by a geotextile filter sleeve which prevents the fine soil particles from entering the central core but allows free entry of pore water into the core. Two types of vertical drains commonly used; the band shaped and the cylindrical shaped vertical drains.
The effectiveness of vertical drains depends on the permeability of the filter and the discharge capacity of the drain. The discharge capacity will be significantly reduced when the filter is pressed into the grooves of the central core due to lateral pressure from the surrounding soils and/or as a result of ground settlement, the drain buckles. Hence, in very soft soils where large settlement is expected, a more rigid cylindrical drain is preferred.
Vertical drains with surcharge to improve soft cohesive soils for structures, industrial buildings, highways, railways, ports and containers, air- ports and runways, oil tanks and other infrastructure utilities