Ground Improvement Specialists.

Bringing innovative cost-effective ground improvement techniques to the UK.

Vertical Drains

Vertical Drains, also known as Wick Drains or Band Drains, are used to accelerate the consolidation of embankments built of fine grain soils. This is normally to expedite construction and limit long term settlement.

The construction of a new embankment or structure induces additional stresses on the ground that can create unacceptable long term settlements during the life of an embankment or structure. A preloading programme can be designed to induce these settlements in an accelerated time frame and minimise the long term residual settlements to be within acceptable limits.

Fine grained soils such as Clays and Silts are usually saturated and therefore, settlements can only occur if the excess water is expelled through the voids in the soil grains and particles. These soils also tend to have a low permeability, and so the reduction of pore water pressure can be a slow process.

Vertical drains consist of a flat or cylindrical plastic core wrapped in a geotechnical fabric, and allow water to drain up through the centre of the drain. These come in a variety of sizes and shapes to meet a variety of soil and site conditions.

Vertical drains can be used to increase the rate of consolidation, delivering substantial programme savings for the build times of earth embankments for many types of land raising schemes.

Prefabricated vertical drains are installed by pushing a hollow steel mandrel, which house the drain material, and are set out on a grid pattern.

The mandrel is driven into the ground by the rig, once at the required depth the mandrel is removed, leaving the vertical drain anchored by a steel anchor plate that holds the drain securely in place.

The mandrel can penetrate soils up to a tip resistance of 5MPa, firmer soils can be penetrated by the use of vibrators or pre-drilling.

A temporary surcharge embankment needs to be combined with the installation of the Vertical Drains in order to expedite full or partial primary consolidation, as well as induce several years of secondary consolidation settlement. Placement of the embankment and the additional temporary surcharge embankment are placed in phases, to avoid the risk of slip failure.

Real time monitoring of the geotechnical parameters, including pore pressures and horizontal displacement, are monitored throughout the consolidation period. These instruments are installed to validate the design and the safe phasing of the embankment construction. These results will also be used to back analyse the design and access the consolidation process

  • Advantages

    • Accelerates the consolidation of fine grained soils
    • Strengthens underlying soil to accommodate superimposed loads
    • Limits long term settlement
  • Applications

    • Earth embankments for all types of land raising
Download the Vertical Drains pdf