Pipe line stability in critical areas of unstable and/or rapidly evolving morphology is a problem of paramount importance not to be overlooked in every pipeline project. The paper deals with the merging aspects of environmental sciences and technical engineering for pipeline stability.
Various environmental and natural hazards with potential risks of substantial damage to submarine pipelines may exist along a selected pipeline route
A considerable number of pipeline damages have occurred because of unpredicted and sudden changes of the original morphology of the sea flooron which they rest. The evolving shape of the sea floor is dependent not only on the local geologic setting and nature of the substrate, as generally thought, but it is strongly influenced by the dynamics of the overlying water mass that makes each marine basin a complex dynamic system. Hydrodynamic conditions of submarine environments are very important factors responsible for the endless modification of sea floor morphology, since submarine currents produce erosion, transport and deposition of sediment.
To identify the hazards which may exist along a proposed pipeline ruote, data must be gathered regarding waves, surface and subsurface currents, and other data.
Environmental and natural hazards can be classified into two main categories hazards which pre-exist and can be encountered during the construction (1.e. pipeline installation) on the seabed and during its planned operational life. The specific hazards and severity of the of these hazards depend on the pipeline-site location, whilst the protection works to be performed and the corrective actions to be taken depend mainly on the water depth and on the type of hazard. In gulf and delta areas the pipeline may be exposed to mud slides and turbidity currents as well as to potential severe storm consequences induced underwater and other major bottom instabilities. In the near shore areas, the pipeline is normally exposed to high hydrodynamic forces and actions if it is just installed on the seabed without any protective trenching. In other areas, depending upon local situations and conditions, pipelines may have to be designed and installed considering earthquakes as well as active faulting which may occur in the area. When installed across straits, channels and narrow seas communicating with larger basins, pipelines may be subject to strong bottom currents, migration and collapse of dunes and sand waves, slumps and other slope instabilities. When laid across wide areas of shallow or relatively shallow seas, the pipeline is very likely to rest across a sequence of aggradation bedforms and sedimentary rhythmic mounded obstruct ion and para1lel depressions which may cause unsupported free spans to the possible extent. Sand waves, dunes and other large, current generated bedforms with a ripple shape may become a major problem in the stability and protection of pipelines crossing wide seabed areas where these structures are present and subject to current induced migration.