With its more than 30 years of experience in water, Tractebel has gathered the expert knowledge necessary for the study of cable trajectories, cable crossings, land-falls and cable laying. One of the most important aspects of cable laying projects is the appropriate definition of the burial requirements, which is an outcome of assessing the risks and installation costs.
During the past decade Tractebel contributed to the development, design and the installation of cables for several offshore wind projects in the North Sea (Belgium, France, UK) and for cable laying projects in the Mediterranean. Based on the experience gained in this projects and relying on experience gained during the execution of the works, Tractebel has developed and adjusted its own methodology to assess and define the most appropriated burial depth and burial technique(s) along offshore cable trajectories. The developed methodology relies on international standards and recommendations. During a cable Burial Risk Assessment Study (BAS) a detailed analysis of the risks and of the possible mitigating measures associated to the design, installation and the maintenance of offshore cables are studied. BAS typically comprises:
- Analysis of the available geotechnical and morphodynamic data and the determination of any significant data gaps needed for the cable installation;
- Analysis of anthropogenic hazards along the cable trajectory: legal requirements, fishing activities, marine traffic, navigation routes, presence of other cables or pipelines, concession and military areas, anomalies, UXOs, natura 2000 areas, ship wrecks,…
- Calculating the Burial Protection Index (BPI) and performing the DNV quantitative risk analysis ;
- Analysis of natural hazards for the cable: current and wave action, sand dunes and seabed mobility, seabed gradient (slope), hard soil and mud, thermal conductivity and organic content of seabed, including the analysis of the Reference Seabed Level and definition of possible mitigating measures ;
- Analysis of the offshore cable pull-in and of the shore landfall design;
- Definition of the recommended burial depths based on the BAS ;
- Technical recommendations for planning and the execution of the works as a result of the mitigating measures identified in the BAS;
- Preliminary recommendations for cable burial / protection techniques and installation techniques;
A BAS is typically prepared during the development and design phases of the project, but adjusted and used in support of the preparation of the works and the execution of the installation works itself. The main value of a BAS consists in providing a solid basis on which Clients base their decisions concerning the most appropriated cable trajectory, the required cable burial depths, the preferred burial / protection techniques, the monitoring and maintenance strategy for offshore cables and the cable micro-routing. A BAS is updated every time that additional data become available (e.g. seabed surveys, marine traffic data...) during the different phases of the project.
References Offshore Cables
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