Vertical drainage has been in use in its current form since the 1970s. Vertical drains are used to considerably reduce construction time. Over the years, the installation technique has improved to the extent that Cofra has installed millions of metres of drain per year and can often be found working on the largest and most challenging projects.
If loads are applied on clay and peat layers, the poor permeability of the layers can lead to excess pore water pressures. If no measures are taken, this excess pore water gradually dissipates and a slow and continuous settlement is measured. This also gives rise to possible stability problems if embankment construction takes place too quickly. Cofra’s MebraDrain system consists of a plastic strip drain that is installed vertically from ground level down to the desired depth. This creates vertical drainage paths in the subsoil, considerably reducing the flow path of the excess pore water. As a result, the consolidation process can be reduced from decades to six months or less and the stability is increased, meaning that embankment construction can take place more quickly.