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Monopile Scour Mitigation

Scour Collar

Wind turbine monopiles can be susceptible to a type of erosion called scour. Especially at sites with tidal currents, a significant section of the soil around a monopile can be removed, due to the effect of the foundation on the local flow pattern and velocities.

The main risks associated with scour are:

  • Reduction of the stability of the foundation
  • Undermining of cables placing stress on connections and riders

Subcon has a large track record in scour mitigation projects. This experience is used to design dedicated offshore wind scour mitigation solutions. An example is our single lift scour collar which take the geotextile back used in Coastmats. Another example can be found in the RipRap grouting solution, originally applied to coastal stabilization projects but found very well suited for monopile scour mitigation.

FAQ’s

Scour is the displacement of sand, soil or clay around a structure induced by vessel wakes, currents, waves and/or tides. Typically the introduction of a hard structure onto the seabed causes flow amplification and vortex eddys. This may be a pipeline, jacket, mono pile or manifold structure. Vortices and flow amplifications tend to transport sediments away from the structure resulting in scour.

Scour is typically mitigated by installing a protective skirt around the structure.

In the case of a monopile this traditionally takes the form of a rock mound installed around the pile. Attempts have been made using rock filter bags and geotextile sand containers. These both have the disadvantage of introducing plastic into the marine environment and cannot be readily decommissioned. They are also unstable in high velocity applications.

Subcon’s scour collar consists of a geoetxile filter layer bonded to the underside of an articulated concrete block collar.

The buoyant fronds in frond mats dissipate the wave and current energy close to the seabed.

The lower velocities have a lower transport capacity as a result, therefore collecting sediment from its surroundings.

Subcon has developed the Single Lift Scour Collar that is used for the scour protection of wind turbine foundations.

This geotectile backed, concrete block mattress provides high performance scour protection for monopiles that significantly decrease the time taken to install scour protection when compared to dumping rock or placing rock filter bags. This solution is ideal for applications where sourcing local rock is not viable or the stabilty requirements exceed that of what rock is able to meet.

The reduced height of the Scour Collar compared to equivalent rock also reduces the risk of secondary scour on the lee side of the monopile.

Scour Collar

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