The Challenge
The installation of 11,000m² of concrete mattress scour protection has begun at the Port of Szczecin carried out by contractor Aarsleff. The primary objective is to increase the berth depth from -10.6m to -12.5m, adding an additional 2 meters to accommodate larger vessels to dock without compromising the quay walls stability.
The berth pocket has been dredged to its maximum depth, with a precise dredging tolerance of 100mm. Extra measures, such as ground anchors at selected locations, have been put in place to maintain the structural integrity of the quay wall. Additionally, the Luxemburg quay (the return wall) was identified as unstable and in need of reinforcement.
The Solution
The formwork, which has been custom-made offsite to meet the precise site requirements for quick installation, is rolled out on the seabed, secured, and then filled with concrete from the quayside. Divers move the filling hose between filler points throughout the process. A total of 71 panels averaging 185m², will be installed. Each panel requires 41m³ of concrete. It is expected that 82m³ of concrete can be filled per day, with each f illing taking about 6 hours. The number of panels installed each day depends on the number of working areas available along the quay and the number of dive teams in use. When deepening existing quays, using the thinnest possible protection maximises the depth achievable with the existing wall. The in-situ concrete mattress creates an interlocking layer that provides sealed scour protection, evenly distributing hydrodynamic forces across the apron and resulting in a stable, thin protective layer. In contrast, rock armour and unsealed mattress systems need extra deadweight to counteract hydrodynamic forces from propeller action and to resist trapped flow pressure. This added weight increases the thickness of the protection required.
The Outcome
To ensure long-term protection, it is vital that the concrete apron is not undermined at its edges. The edges of the apron are placed in a trench, which includes a hinged edge block detail. These hinged edge (HE) blocks are tied into the main concrete apron, weigh 4t each, and are designed to drop independently, giving the apron additional protection against scour before any maintenance is needed. The HE blocks are heavy enough to resist being flipped by trapped flow pressure.
