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Vertical drains

Since the development of the synthetic prefabricated vertical drain (PVD) also known as wick drain in the late 1970ties, Cofra is worldwide one of the leading contractors. Cofra has installation rigs available for each soil type, varying from very soft soils to very stiff intermediate layers. Installing worldwide, we encounter depths of 3 to over 60 meter! Our heavy installation sets are the strongest in the world and able to penetrate 25 to 30MPa sands. For working offshore, we have the necessary experience and equipment. Our installation rigs are designed for containerized transport and thus easy to ship to any project location in the world.

What it is

This techniques involves the installation of artificial drainage paths or vertical drains into soft compressible soils. The prefabricated vertical drain (PVD) used by Cofra are specially designed to work effectively under high settlements (i.e. under buckled or kinked conditions). 

How it works

Highly permeable soils like sand can adjust rapidly to loads and the corresponding compression / reduction in voids due to the ability to easily drain the excess porewater. Low permeable soils like clay and peat do not have this ability and show a delayed compression with the dissipation of the excess pore water. This process of dissipation of excess pore pressures, also known as consolidation, can take up to years depending on the thickness of the deposit. Vertical drains or also known as wick drains are used to shorten the dissipation path of the excess pore water and to accelerate the consolidation process to a few months or even weeks when the PVD is placed at close center to center distances.

PVD Working

Why it's used

Vertical drains are used to accelerate the consolidation and reduce the consolidation period such that it fits within regular construction schedules. It also makes it possible to control and design for relative strict residual settlement requirements. The acceleration of the consolidation process has also the advantage that a faster lifting schedule of an embankment can be used. The strength of the subsoil has a relation with the degree of consolidation (adjustment of the subsoil to the placed load).

Application areas

Vertical drains are used in the following markets:

  • Infrastructure: The drains are for example used for the construction of embankments for roads, railways, the preloading of runways and aprons for airports and infilling of port areas
  • Dredging and land reclamation: Drains are used when reclamations are constructed on soft deposits
  • Mining: Drains are used in Tailing ponds to accelerate consolidation or to increase the leaching effect in use embankments
  • Construction: Drains are used to make green and brownfield areas suitable for construction of for example houses, warehouses and tank farms by reducing the residual settlement of the terrain
  • Flood protection: Drains are used in the flood protection market to increase the stability of dikes and embankments during widening projects.

The following soil types are suitable for the use of PVD:

Website Diagram PVD V2

Find out more details about our offshore installation capabilities on this page

How it is installed

The prefabricated vertical drains are installed using the wide range of stitchers, developed in-house by Cofra. The principal of installation of the vertical drainage is based on the insertion of a steel mandrel into the ground with a drain inside. The drain extension at the bottom of the mandrel can be connected to an anchor plate or stick to help the anchoring of the drain. Automatic anchoring systems are also available keeping the drain at depth during retraction of the mandrel. After the mandrel has reached the surface, the drain is cut and a new anchor plate is connected to the bottom of the next drain. The mandrel is pushed into and retracted from the ground through a system of cylinders and winches, which in turn are propelled by the excavators’ hydraulic system.

Csm Drain Wide Dd407ddb90

Video of a Dutch Project

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Estimation Department Cofra

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Technical Sales Cofra

For design questions or technical information.

A selection of our consolidation projects

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PVD installation through very dense sand layer Chek Lap Kok Link, Hong Kong

In 2016, Cofra Singapore installed 1,600,000m1 drain up to a depth of 45m using our heavy push rig, pushing through the dense sand layer at 20m of depth without predrilling.


PVD installation highway widening SAAone A1/A6 Diemen - Almere

In 2016, we installed 7,500,000m1 of prefabricated vertical drains, with an installation depth up to 7m.


PVD installation for housing estate West Hythe phase 1-6, UK

Between 2016 and 2019, Cofra Ltd installed around 400.000 m1 of prefabricated vertical drains, each year.


PVD installation for Distribution Plot, Swindon

In 2018, Cofra ltd installed 205,000m1 of prefabricated vertical drains.


PVD installation Tuas Finger One reclamation, Singapore

Between 2016 and 2019, we installed 5,800,000m1 of prefabricated vertical drains, with an installation depth up to 35m.


PVD installation LNG plant Soyo reclamation

In 2008, we installed 2,300,000m1 of prefabricated vertical drains, with an installation depth up to 25m.