Concept
Offshore geotechnical engineering is a sub-field of geotechnical engineering. It is concerned with foundation design, construction, maintenance and decommissioning for human-made structures in the sea. Oil platforms, artificial islands and submarine pipelines are examples of such structures. The seabed has to be able to withstand the weight of these structures and the applied loads. Geohazards must also be taken into account. The need for offshore developments stems from a gradual depletion of hydrocarbon reserves onshore or near the coastlines, as new fields are being developed at greater distances offshore and in deeper water, with a corresponding adaptation of the offshore site investigations. Today, there are more than 7,000 offshore platforms operating at a water depth up to and exceeding 2000 m. A typical field development extends over tens of square kilometers, and may comprise several fixed structures, infield flowlines with an export pipeline either to the shoreline or connected to a regional trunkline. An offshore environment has several implications for geotechnical engineering. These include the following: Ground improvement (on the seabed) and site investigation are expensive. Soil conditions are unusual (e.g. presence of carbonates, shallow gas). Offshore structures are tall, often extending over above their foundation. Offshore structures typically have to contend with significant lateral loads (i.e. large moment loading relative to the weight of the structure). Cyclic loading can be a major design issue. Offshore structures are exposed to a wider range of geohazards. The codes and technical standards are different from those used for onshore developments. Design focuses on ultimate limit state as opposed to deformation. Design modifications during construction are either unfeasible or very expensive. The design life of these structures often ranges between 25–50 years. The environmental and financial costs in case of failure can be higher.
