Project Requirement
The catastrophic failure of the Port-au-Prince container jetty during the 2010 earthquake highlighted the need for a resilient, long-term scour protection system capable of resisting both hydraulic forces and the effects of future ground movements. The design brief required a replacement piled jetty that could be rapidly constructed with robust slope protection to prevent undercutting and slope instability, particularly given the complex subsoil conditions—predominantly sand with zones of gravel and intermittent clay layers. It was critical that the selected scour protection could be installed efficiently beneath the deck and between densely spaced piles, all while accommodating variable underwater slopes and working tolerances.
Concrete Mattress Solution
A new piled jetty for container vessels is being constructed at Port au Prince following the 2010 earthquake, when the old jetty slipped into the sea due to liquefaction.
The new jetty is using a innovative construction technique. Steel shell piles are being driven by land based piling plant to save on marine piling costs and then the jetty berth and slope is dredged and excavated from land by long reach excavators working around the piles.
System Composition:
Constant Thickness (CT) mattress panels were specified for the lower, high-energy sections of the slope, providing a robust, impermeable barrier against the erosive forces of bow thrusters and vessel propellers. Higher on the slope, where wave and tidal effects predominate, Filter Point (FP) mattress panels were used, their engineered permeability helping to relieve uplift pressures and reduce the risk of hydraulic instability.
At the slope toe, a riprap falling apron was installed as a sacrificial edge detail, forming a flexible transition between the mattress and the seabed and providing additional protection against edge scour and undermining.
Soil Stabilisation:
Before installation of slope protection, the foundation soils were densified by vibrocompaction, supplemented with stone columns in areas of greater susceptibility to liquefaction. The aim was to achieve a stable working platform and limit future settlement or deformation beneath the mattresses.
Tolerance and Detailing:
The underwater slope was prepared to strict tolerances—+0.3 m above, −0.45 m below design profile—recognising the practical limits of underwater excavation and the importance of ensuring full mattress contact with the slope. Slope preparation included formation of a toe trench to seat the mattress and prevent migration, which was critical to the system’s overall performance.
Each concrete mattress panel was prefabricated on land to match the plan geometry between piles. Mattress panels were sized to span the full bay width, minimising the number of underwater joints and the associated installation risks. Additional allowance in the mattress layout (+5%) was incorporated to accommodate pile installation tolerances and the irregularities of underwater excavation.
Pile Seals
Specially engineered seals were developed to ensure a watertight interface between the mattress and the numerous steel and concrete piles. These seals consisted of custom-formed collars in the mattress fabric, which could be drawn tight around the pile and locked in place, preventing grout loss and minimising the risk of washout during service.
Land Infill Construction
A key innovation on this project was the adoption of the ‘land infill’ method. The initial stages—including pile driving, vibrocompaction, and reinforced concrete beam construction—were carried out from a temporary sand platform, built out into the bay. This allowed heavy plant to operate in the dry, significantly improving construction speed and reducing the reliance on marine equipment.
Once the superstructure was in place, underwater slope excavation commenced. Long-reach excavators operated between deck beams to remove bulk material, working to within tolerance of the final profile. Final shaping of the slope and toe trench, particularly under beams and around piles, required the use of diver-directed water jetting to achieve the required precision and to avoid damaging structural elements. The excavation and slope preparation process was the rate-determining step for the whole operation, as accurate bed preparation is essential to successful mattress installation.
Mattress Deployment:
Concrete mattress panels were bundled, floated out over the prepared slope, and positioned with the aid of divers. Each panel was aligned and fixed around piles using the preformed seals, then zipped to adjacent panels using corrosion-resistant fasteners to form a continuous apron. This underwater assembly required careful coordination, but typically a full bay panel could be installed in two to three hours.
Micro Concrete Filling:
With the mattress panels secured in place, filling commenced from the lowest point of the slope, progressing upwards to expel trapped air and ensure full compaction beneath the fabric. A micro concrete mix was developed for this project—based on a 2:1 sand-to-cement ratio and using locally sourced aggregates—chosen for its high flowability and strength gain properties. The concrete was delivered by ready-mix wagons and pumped through a worm pump using 50 mm grout hoses. Divers inserted the hose into each mattress filling sleeve and controlled the rate of placement in a tremie-like fashion, ensuring that the mix travelled throughout the panel and filled the intricate geometry around piles and beams.
The physical properties of the mattress formwork fabric played a crucial role. The formwork was engineered to be permeable to water, allowing excess mix water to bleed out and ensuring a dense, high-strength concrete set within the mattress. The ball-and-socket joint configuration between adjacent panels provided interlocking and resistance to differential movement.
Each panel typically required 6–8 hours to fill and finish, with overall progress dictated by the speed of bed preparation rather than mattress placement itself.
Edge Protection:
Once the mattress apron was in place, rock edge aprons were placed manually around the platform perimeter. These served as a falling edge, providing a dynamic buffer to absorb local scour action and protecting the edge of the concrete apron from being undercut.
Performance and Advantages
The Port-au-Prince project demonstrated that in-situ concrete mattresses could be installed quickly and reliably beneath a piled jetty, even in challenging ground and underwater conditions. The solution allowed for concurrent construction of the jetty superstructure and underwater protection, offering significant programme savings compared to traditional rock armour, which typically must be placed before deck construction.
The high degree of adaptability—both in mattress panel geometry and in installation technique—meant that construction could proceed efficiently despite pile and bed tolerances. Purpose-designed pile seals and careful slope preparation provided a robust, sealed system with long-term durability against hydraulic action and ground movement.
Proserve supported both the design and site installation phases, working closely with Technital (the designer) and GLF (the main contractor) to develop practical solutions to the engineering and constructability challenges.
The completed jetty now provides vital container handling infrastructure for Haiti, supporting both ongoing recovery from the earthquake and future economic development
