Piled Jetty Scour Protection
Concrete mattress provides unique revetment protection from both vessel and wave action. A sealed concrete apron to the wall and around the piles, prefabricated porosity holes enable effective wave run down, ensuring the slab is not lifted. The system has 50 years of proven usage on revetments.
Revetment Scour
The geotechnical stability of slopes surrounding piled jetties in ports is a critical factor in ensuring the structural integrity and longevity of these maritime infrastructures. Piled jetties are often exposed to significant environmental forces, including wave action and vessel-induced currents, which can lead to scour – the removal of sediment around the piles and slope areas. Without adequate protection, this scour can undermine the slopes, causing erosion and instability, potentially leading to structural failure.
To mitigate these risks, effective scour protection measures such as mattresses or rock armours are essential. These measures help maintain the stability of the slopes by absorbing and dissipating the energy of waves and currents, thus preventing the erosion of sediments and ensuring the continued safe operation of the jetties
Mattress Advantages
Concrete mattresses offer significant advantages over traditional rock armour for scour protection at piled jetties, particularly regarding installation and logistical efficiency. One key benefit is that concrete mattresses can be installed beneath the jetty deck, allowing scour protection work to proceed independently of other construction activities. This flexibility means that work on the deck can continue simultaneously, removing scour protection from the critical path and significantly improving project scheduling.
The concrete apron formed by the mattresses effectively distributes hydrodynamic forces across the entire surface, providing a stable and robust barrier against scour. In contrast, rock armour relies on the individual deadweight of each rock to prevent displacement, requiring rocks to be up to seven times thicker than an equivalent concrete mattress. Due to the specific size and weight of the required rock, suitable materials may not be available locally, making sourcing challenging. Transporting these large rocks from distant locations can be prohibitively expensive, further complicating the logistics and increasing project costs.
By eliminating the need for large, hard-to-source rock units and providing a streamlined installation process, concrete mattresses offer a more practical and cost-effective solution for maintaining geotechnical stability. This approach ensures efficient project completion and reduces delays, making concrete mattresses the preferred choice for scour protection at piled jetties.
Jetty Refurbishment
When refurbishing or deepening an existing jetty, concrete mattress enables scour works to again proceed under the deck. Localised water dredging can be used to prepare the slope ready for mattress installation.
Design Concepts
- Continuous concrete apron
- Sealed apron
- Porosity & deadweight for wave run-down
Pile Seal
Seals around piles are a critical area for protection and must form a sand-tight connection with the pile to prevent any loss of material at the connection point. Proserve has developed an interior pile bolster that not only helps to secure the mattress around the pile during filling but also provides built-in tolerance for additional concrete to form around the pile, ensuring a reliable seal is achieved on every pile. The integration of the pile bolster into the mattress means it fills simultaneously with the rest of the mattress, eliminating any overlaps or gaps.
Effective Wave Run Down
Wave action can fail mattress through cracking. The concrete apron can be repeatedly worked in the tidal zone, with pressure lifting the mattress. Porosity and increased deadweight in the wave zone enables effective wave run down and stability. To date the maximum wave height mattress has been designed to is 2.3m. A stone layer with a larger diameter than the porosity holes is laid under the mattress in the wave zone, ensuring no loss of bed material.
Installation
- Roll out
- Attach around piles
- Zip to neighbour
- Fill in tremie fashion from the bottom of the slope
Proserve's Experience and On-Site Support
Proserve supports contractors from the tender stage through to the design phase, ensuring a practical solution that aligns with PIANC standards and can be effectively constructed on-site. We tailor the formwork in-house to meet the required specifications, minimising the amount of work needed from the dive team. Our engineers collaborate with contractors to help prepare the necessary mix using local materials and ensure readiness for swift and efficient construction.
With over 50 years of experience with mattress on piled jetties helping contractors managing key construction issue such as:-
Sliding Mattress While Filling
- On a slope its possible during filling that the mattress can slide down the slope with poor restraint.
- Working down the slope rather than across ensures the formwork can be restrained at the piles rather than continuously across the slope horizontally during filling.
Fluidity Management
- Once the designed mix has been selected for the required strength managing pump-ability is critical. Hose blockages and the mix not flowing through the mattress will cause delays and lead to pressure build ups.
- Simply fluidity testing each batch of mix can ensure the mix is on spec, passing the mix through a cone is quick and simple. Also is adding additional water to the mix if required.
