Challenges in Design-Build a Vertical Breakwater/Quay for a New Bulk Terminal in Oceanic Conditions

Abstract: A new bulk terminal, intended for the loading /unloading of both dry and liquid bulk materials, is foreseen on the western African coast. The facility, being approximately 3.0km offshore, will feature an L-shaped combined quay-vertical breakwater, which will also serve as a quay structure for berthing two vessels.
The terminal is constructed by plain, vertical faced caissons and is connected to the land by a 3km- long trestle bridge. The natural depths at the port area vary between -15.0 and -18.0 m CD.
Due to the adverse oceanic climate and the stringent downtime requirements by the Port Owner, a multi-faceted approach was followed for concluding with the marine design aspects, among others, the verification of the overall layout, wave loads, overtopping, toe protection and engineering of the construction support works.
More specifically the followed approach covered the below steps:
1. NUMERICAL MODELING
The location of the new port, apart from the oceanic conditions, is characterized by the presence of infragravity (IG) waves, arising from the reflection of swells on the mild sloping coast. A wave recording campaign was conducted for one summer and two consecutive winter periods, each covering two months, to adequately document the local characteristics of the IG waves.
These measurements were used to calibrate a large (14.0 km x 7.0 km) wave model to accurately simulate the wave regime and more importantly the IG waves at the lee of the breakwater.
In addition to the wave modeling, the design and verification of the port’s various features were elaborated through an extensive series of numerical models:
• Full mission bridge navigation simulation,
• Dynamic Mooring Analysis
• Dredge plume dispersion modeling.
2. PHYSICAL MODEL TESTS
The vertical walls of the breakwater/quay result in significant challenges in terms of wave pressures, toe stability, overtopping and agitation. These were addressed by carrying out both 2D and 3D physical model testing (PMT). The 2D PMT was undertaken for typical sections of the breakwater at a model scale of 1:55 for measuring wave pressures, overtopping, and transmission due to overtopping. Additionally, the wave reflection from the vertical walls and the stability of the seaside toe were also assessed. The 3D PMT was performed at a scale of 1:60. The testing resulted in optimizations of the wave wall, to reduce overtopping due to phenomena related to oblique wave incidence, and the toe stability with emphasis on the roundheads where 3D effects proved to be significant.

3. CONSTRUCTION WORKS ENGINEERING SUPPORT
The location at a coastline offering no shelter and in adverse oceanic conditions, necessitated for the engineering of a large temporary harbour to allow for caisson construction, launching, the loading of necessary materials and also partial sheltering of Single Point Moorings designed to service the multitude of vessels required for construction operations.
Finally, a dedicated weather window analysis was also conducted to assess the available weather windows on a seasonal and yearly basis, allowing to properly schedule the weather-sensitive caisson launching and installation operations.

How does this project / topic contribute to the advancement of the industry and profession?: The project is located at a remote area which is subjected to harsh oceanic climate and as such a very wide range of the available design tools had to be implemented in an integrated manner to allow for the conclusion of the design for such a demanding project. This approach and the discussion of the additional challenges that emerged during this process, will assist port engineers dealing with similar projects to execute them in cost-effective and timely manner.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: Although the followed process was not innovative per se, the magnitude of the project and corresponding challenges imposed by the adverse environment have indeed tested the limits of the available engineering tools.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: The marine-related design of the project has been finalized recently. In retrospect, the biggest challenge faced was the timely coordination of all the involved stakeholders and the seamless integration of their feedback to produce the optimum result considering also many constructability challenges. This has been successfully achieved thanks to a robust design works schedule elaborated by the Archirodon engineering team.

Who is the target audience for this paper?: Maritime/Coastal engineers, marine terminal operators, oceanographers and marine hydrodynamics modelers. The writers team, being themselves maritime engineers working in the Construction industry, can tap into a decades- long experience of one of the leading companies in the maritime construction field (Archirodon N.V.) showcasing an impressive track record of successful projects around the globe.