Cofra - Vacuum Consolidation Systems
From Consolidation
Cofra has a long track record in the field of vacuum consolidation. We have multiple vacuum consolidation systems within our range of techniques, amongst which Beaudrain, BeauDrain-S and the traditional vacuum consolidation method using a synthetic liner. All concepts, except for the BeauDrain system which uses an in-house developed special plough, are installed by using our own PVD rigs. Every system has its own solution to overcome loss of vacuum in sand layers. Ask us about the possibilities.
What it is
This techniques involves the installation of artificial drainage paths or vertical drains into soft compressible soils with a lowering of the atmospheric pressure inside the drains to accelerate the consolidation process. The prefabricated vertical drain (PVD) used by Cofra for vacuum consolidation are specially designed to work effectively both under high settlements (i.e. under buckled or kinked conditions) and under the vacuum pressure.
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.
Vacuum consolidation acts, in principal, similar to prefabricated vertical drains (PVD) with surcharge. However an additional load is applied to the subsoil by lowering the atmospheric pressure inside the vertical drain. The applied vacuum pressure inside the system can be seen as an equivalent surcharge load. This means that the total applied pressure (surcharge load plus vacuum load) acts at the soil in order to accelerate the consolidation. This principle is the same for all vacuum methods. The difference between the methods is their application area caused by the ability of each system to seal the vacuum drains from ingress of air or permeable layers. The liner vacuum system uses a top liner and slurry walls around the area to seal the soil completely from air. The BeauDrain system installs the complete system below the ground water in the soft compressible soil with the help of a plough. BeauDrain-S uses tubes to cross any permeable layers and connects to a PVD in the soft material below the ground water. Please refer to the image below for more information.
Why it`s used
Vacuum consolidation is often used to solve stability problems and create with the vacuum loading, which does not cause a driving moment for the instability, additional strength in the subsoil to accommodate for a faster surcharging schedule or a reduction in surcharge to limit the residual settlements. In countries with limited or very expensive surcharge, vacuum can be a good alternative to save costs. In rare cases vacuum consolidation is also used to limit horizontal deformations.
Application Areas
Vacuum consolidation is used in the following markets:
- Infrastructure: Vacuum consolidation is for example used for the construction of embankments for roads, railways, the preloading of runways and aprons for airports and infilling of port areas on soft deposits where stability is a major issue of surcharge is scarce
- Dredging and land reclamation: Vacuum consolidation can be used when reclamations are constructed on soft deposits and horizontal deformations need to be reduced
- Mining: vacuum consolidation is highly suitable for the used in Tailing ponds to create strength without the application of surcharge. The vacuum system can be installed from a barge or specialized custom made tools.
- Construction: Vacuum consolidation is 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: vacuum consolidation is in the flood protection market to increase the stability of dikes and embankments during widening projects.
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