Design of Marine Pipelines for Areas of Unstable Sediment

Burial of marine pipelines is the preferred method of improving long-term performance. Embedment is achieved with a jet sled that erodes a trench of the desired depth whereby natural processes fill the trench. Specifications usually require that embedment exceed 3 ft at water depths of 200 ft or less. The objectives of burial are to isolate the line from anticipated hazards such as wave forces, fish trawl damage, and erosion. This solution assumes that the seabed provides a stable, rigid protective coating for the pipeline, an assumption that is often erroneous. Over the length of a pipeline there are many geological processes that are capable of influencing the performance of a pipeline. The processes occur at varying rates and may be intermittent or continuous in nature. Site surveys are usually performed to detect there processes. However, a brief survey may not reveal significant processes that occur over a 10-yr to 20-yr span. Nevertheless, an understanding of the mechanisms that lead to overstressing of pipelines and long-term failure can lead to improved design and instillation methodology for unstable areas. This analysis is concerned with the mechanism of sediment mass movement on the magnitude of pipeline tension.