Jack-up rig engineering - ensuring safe foundations
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| PLAXIS 3D Analysis of Skirted Mudmat-Soil Interaction Application to Oil Platforms and Windmill Transformer Stations |
Self-elevating mobile units, jack-up platforms, perform offshore drillings in water depths up to 150 m or more. Engineering assessment of jack-up rig foundations is one of GEO's Geotechnical Engineering Department fields of consultancy. This is considered a great challenge, taking into account the size of such structures, their locations all around the world with variety in geology and offshore soil conditions, the increased tendency for installations in deep water and the expected environmental changes and weather hazards.
Prediction of footing penetration during preloading punch through risk assessment
Evaluation of the soil conditions and engineering assessment of spudcan penetrations for rig installations at specific locations all around the world, is one of the main products GEO delivers to its clients. The soil conditions are assessed based of the available soil data explored during site investigations carried out by different geotechnical companies and delivered to GEO by the rig owners. Our engineering assessment is based on conventional analyses (GEO's in house program) and finite element method using programs like Plaxis, Abaqus or Elfen when multi-layered, critical soil conditions are encountered. The main issue is punch through risk assessment.
Foundation stability after preloading, sliding and fixity
Design of jack-up foundations is based on their capacity / integrity under monotonic combined vertical, moment and horizontal loads as limiting conditions due to environmental impacts. As part of the design GEO carry out conventional (V-H-M) analyses (GEO in house program). As this approach might not always be reliable for combined loads acting on a three-dimensional (3D) footing geometry located on layered soil conditions and for footings equipped with skirts, enhancing additional moment capacity due to suction, finite element analyses of the spudcan-soil interaction are applied.
Spudcan interaction with other structures
During jack-up installations in locations close to a fixed oil platform, a harbour area, structures lying on the seabed etc. the interaction of the spudcans with those structures such as platform pile foundations, quay walls, pipelines etc. is generally assessed. In addition, the behaviour of the spudcans with / without skirts in interaction with the jack-up structure are investigated when there are disturbances / footprints in the seabed from previous rig installations or the seabed is inclined or consists of non-uniform undulating layers. Such assessments are generally based on the finite element modelling.
Following international guidelines
GEO's engineering consultancy for jack-up rig foundations follows the international (SNAME, DNV, ISO) as well as the Danish guidelines and has rapidly increased during the years. A database covering soil investigations offshore is established and continuously updates.
Course on jack-up rig foundations
When requested by its clients GEO holds a geotechnical engineering course applicable to jack-up rig foundations. New developments in the analysis with illustrations from completed or upcoming projects are discussed.
For more information on our jack-up engineering services and the course, please contact Project Director, Civil Engineer Ph.D. Lindita Kellezi, lke@geo.dk.
Recent publications on jack-up rig foundations
GEO recent developments in the jack-up rig foundation engineering are also published or presented in international conferences. Some of our articles can be found on the frontpage under:
For more on GEO's laboratory, see: