What is a Filter Unit?
Filter Units are designed to protect rivers, shores, bridges and mono piles from scour damage. A Filter Unit is constructed of mesh net filled with rocks. The units prevent scour without destroying the environment as they provide a natural habitat for plants and aquatic life.
Filter Units are also used to provide environmentally-friendly marine cable protection.
Filter Units are used for…
1. Scour protection at the base of wind turbines
2. Cable and pipeline protection and as a counter measure to the problem of pipeline movement.
3. Adjusting an uneven seabed when laying cables and pipelines.
4. The creation of cable and pipeline crossings.
Features of Filter Units…
Cables can be laid on uneven seabed areas without the need for levelling.
Filter Units are used to fill in gaps on an area of uneven seabed.
Ease of Installation
As Filter Units are flexible and fit well together it is possible to easily add more as needed.
Filter Units installed on seabed.
The units will follow the structure of the seabed even if scouring or sinking occurs.
It is easy to carry out remedial work or to add more units.
For example, carrying out maintenance on a rock dumping site.
Rocks covering marine cable.
Rocks are washed away by flow of water.
Repair work using Filter Units.
Cost Effective Installation
It is possible to install multiple Filter Units at once by crane.
Image of installation of three Filter Units at one time.
Scour Protection and Suction Prevention
The layers of flexible units provide high coverage protecting the seabed from scouring and sucking.
As Filter Units are made of synthetic fibre they can withstand corrosion and have excellent longevity, e.g. 30 years durability to ultraviolet rays.
Weather test of net (acceleration test of ultraviolet rays irradiation for 7500 hours equivalent to 30 years’ exposure under the sun.)
Consideration for environmental issues
Each Filter Unit has a porous structure so it can become a habitat for aquatic creatures.
At the same time, the stable ground created by the Filter Unit becomes a base of growth* for seaweeds etc.
* The growth of seaweeds depends on environmental condition of the sea.
Shape Of Filter Unit Before Stuffing Stones
Dimensions In Meters, Filter Unit Installed
There is a risk of damage to Filter Units if they are used in certain places:
- Wave breaking points where waves hit constantly. (The stones could rub the net from inside causing it to break.)
- Areas where there are a lot of stones on the seabed. Filter Units may be impacted by stones and partially broken during stormy weather.
- Above applicable velocity of flow is a theoretical value when Filter Unit is installed in seawater.
We recommend using stones of 50mm diameter for 2t & 4t types and 75mm for 8t type. However, it is possible to use a maximum diameter of 200mm for all types.
*Specific gravity of filling stones should be 2.6-2.65.