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Offshore Geotechnical Engineering

Updated 26.04 2013

Pipe Soil Interaction

General
Pipelines, flexibles and umbilicals are installed by Subsea 7. As part of the installation analysis, a geotechnical assessment of the pipe-soil interaction is performed.

The installed pipelines or flexibles will frequently need protection. This protection comprise of rock dump or backfill from trenching activities. The pipelines and flexibles may expand due to the pressure in the products leading forces interacting between soil and pipe. The geotechnical assessment of these forces are called pipe-soil interaction.

Trenched products
Pipelines, flexibles and umbilicals are often trench by either jetting or ploughing. DNV-RP-F110 does provide geotechnical approaches on how to determine uplift resistance and downward resistance for trenched pipes; however, no appropriate recommendations are given for lateral resistance of trenched pipelines. Subsea 7's geotechnical team has developed approaches to assess lateral resistance.

Rock dumped products
On soil inappropriate for trenching, rock are typically installed for the protection of pipelines. Rock dump consist of crushed rock from quarries and generally has a particle size between 1 inch and 5 inch. No geotechnical design codes or papers seem to have appropriate methodologies described to assess pipe-soil interaction in a rock dump. Subsea 7's geotechnical team has developed approaches for the geotechnical assessment of a rock dumped pipeline.

Below is a picture taken during small-scale testing of plastic deformation in a rock berm during lateral pipeline displacement. Obviously, the test setup is not not in accordance to good engineering practice for doing model testing, but it provides a great visualisation of lateral pipeline displacement.