Prefabricated vertical drains

  • Prefabricated vertical drains | MebraDrain

    Prefabricated vertical drains are used for settlement process and to accelerate the decline in waterspan. Geotechnics is a proven partner in the field of civil engineering for the production of prefabricated vertical drains. Its ability to respond proactively to customers’ requests and the custom production of the MebraDrain system, make Geotechnics a prominent market leader with an international customer base. Geotechnics has a modern factory that dispenses products out to its customers all over the world. Thanks to the high quality and the monitoring of products in our own laboratory, Geotechnics is in great demand as a project partner in numerous drainage projects. Vertical drains are also called PVD, band drains, prebafricated vertical drains (PVD) or wick drains.

  • Prefabricated vertical drains

Description

The MebraDrain product
MebraDrain is a prefabricated strip made of plastic that is well suited for water drainage. The flexible core is made of high-quality polypropylene. Channels, through which water can flow unimpeded, run over the entire length on both sides. This core is surrounded by a strong and durable filter that combines a high degree of water permeability with an excellent impassable soil barrier.

Why MebraDrain?
MebraDrain prefebricated vertical drains is available in several types, the MD7407, MD7007 and MD88-H, each suitable for certain project-specific conditions such as soil conditions and installation depth. Moreover, Geotechnics also produces a custom-made drain under the name MD88-HD that can be dimensioned to meet the requirements of the design. The MebraDrain prefabricated vertical drainage system has become one of the most frequently used vertical drainage systems in the world. This frequent use of MebraDrain prefabricated vertical drains in numerous projects around the world is clear proof of the trust customers have in our product. More than half a billion metres MebraDrain have now been installed worldwide.

Applications

Prefabricated vertical drains applications

If loads are applied on clay and peat layers, the poor permeability of the layers can lead to perched pore water. If no measures are taken, this perched pore water gradually flows away and will slowly alter the settlement. This can also lead to possible stability problems if embankment construction takes place too quickly. MebraDrain system consists of a plastic strip drain that is installed vertically from ground level down to the desired depth. This causes vertical drainage paths in the subsoil, considerably reducing the flow path of the perched water. As a result, the consolidation process can be reduced from decades to six months or less and the increase in stability is accelerated, meaning that embankment construction can take place more quickly

Specifications & Documentation

Design

Design information prefabricated vertical drains
The required prefabricated vertical drain distance and installation depth of prefabricated vertical drains are dependent on the project and are determined using design calculations. The drain distance is highly dependent on the available time for the consolidation process and on the requirements with regards to the residual settlements after the construction period. The depth of installation is in its turn dependent on the local geology and geohydrological conditions.

There are, next to simple formulas for a 1-layer system, several calculation methods available for the design of prefebricated vertical drains, like the Dutch Koppejan method and several isotach methods. These methods are programmed into commercial software to make calculations easier. A well known software package in Holland is Msettle (delftgeosystems), able to calculate, next to a drain distance, the settlements and residual settlement also the application of BeauDrain.

Cofra uses, next to Msettle, an internally developed program based on the isotach theory. Cofra is able to provide you with the complete design package for small and large projects, by using the expertise of Hydronamic, the engineering firm of Boskalis Westminster, with over 10 geotechnical engineers. Two of them are resident engineers based in Amsterdam. Next to design work, second opinions can be given on completed designs.

The calculations, using the internally developed calculation program, are performed for a multi layered 1 dimensional profile using the isotach theory of Yin and Graham 1989 with Terzaghi consolidation. The drains are modeled using the derivation of Barron-Carillo. It is possible to model, within the calculation model, a staged construction with and without vertical drains and calculate the settlement, residual settlement and degree of consolidation in time.

In the case you would like us to perform a design, the following information is required:

Geometry

  • Existing surface level
  • Future surface level
  • Waterlevel
  • Sketch indicating the area and location where the ground improvement is required

Geotechnical data

  • Soil profiles ( boreholes, SPT data, CPT data)
  • Geotechnical parameters ( unit weights, compressibility characteristics of the soil)

Operational figures

  • Maximum extend of the consolidation period
  • Wishes with regards to surcharge levels or drain distances

Requirements

  • Settlement, residual settlement or minimal degree of consolidation demands

In the case you have only a limited amount of data available for the design, you can always contact our geotechnical department in order to see if we can perform a design using the available data, or whether there is a need for additional site investigation.

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