Scour Protection
Piled revetments are highly exposed to hydrodynamic forces and can suffer significant erosion from both vessel propulsion and wave action. Propeller wash and thrusters generate high-velocity flows that displace seabed material at the toe and around pile foundations, while repeated wave loading contributes to ongoing sediment movement and scour. If left unmitigated, this erosion can undermine the seabed support, reduce pile embedment, and ultimately compromise the stability and structural performance of the revetment.
To address these risks, scour protection systems such as rock armour aprons, concrete mattresses, or grout bag installations are commonly applied to stabilise the seabed, absorb hydraulic energy, and prevent soil loss. By providing this layer of protection, the integrity and longevity of piled revetments are preserved, ensuring safe and reliable performance in demanding marine environments.
Historically, rock protection has been most commonly used. However, larger stone sizes are now generally required to resist action from modern propulsion types, making rock less cost-effective. There are also construction difficulties to overcome forming rock layers around piles on slopes.
Concrete Mattress Solution
Fabric-formed concrete mattresses create a plain slab of uniform thickness with fully interlocking shear joints, producing a continuous and stable concrete apron. The system is designed to form sand-tight seals around piles, achieve a secure bond to the quay wall, and provide edge protection through embedment or rock armouring. By creating a continuous, sealed slab, the mattress efficiently distributes hydrodynamic forces, making it highly effective in conditions with low vessel clearance and high propulsion velocities.
In the wave zone, the mattress is engineered with controlled porosity, tailored to the expected wave height, which enhances permeability and allows effective wave rundown while maintaining the structural integrity of the slab. Typical thicknesses are 220 mm in the wave zone and 150 mm in submerged areas, optimising strength and durability in each exposure condition. With over 35 years of proven performance on piled revetments, this system offers a long-term, reliable solution for scour protection in demanding marine environments.
Installation
The fabric formwork is custom-tailored to suit each structure, allowing a continuous slab and controlled installation to be achieved with ease. Owing to its lightweight nature before filling, the system can be handled efficiently and even installed beneath deck structures where access is restricted. As the formwork is pump-filled in situ, precise dredging or extensive seabed preparation is not required; instead, the mattress naturally conforms to the tolerances and undulations of the revetment. Installation is carried out by divers, who lay out the formwork, secure it around piles, and zip-connect it to adjacent panels, creating a continuous interlocked apron.
A 2:1 sand–cement micro-concrete mix, designed to achieve a compressive strength of 35 N/mm², is supplied directly from ready-mix wagons and pumped into the formwork panels from the bottom upwards via grout hoses lowered from the deck above. This method ensures complete filling, eliminates voids, and produces a dense, durable slab capable of long-term scour protection in demanding marine conditions.
Advantages
- Can be installed under the deck ensuring works on above the deck can continue
- Much thinner protection than multiple layers of rock armour
- Expensive marine plant not required for installation
- Better joints and performance than preformed mattress protections
- Copes effectively with revetment tolerances