Location
Arlington, Virginia
Date
14 Aug 2008, 7:00 pm - 8:30 pm
Abstract
The paper focuses on the geotechnical design issues facing the design team responsible for the provision of an offshore Gravity Base Structure (GBS) to act as a clump weight for a Power Buoy located in the Lyell field of the northern North Sea, United Kingdom. The structure is to be positioned on the seabed, where ground conditions are considered variable but in general comprise of a surface layer of loose to very dense silty sand, underlain by a thick sequence of firm to very stiff sandy clay. Geotechnical data specific to the location of the GBS is limited; problems encountered during testing allowed only three cone penetration tests to be carried out to maximum depth of 12m and sampling for subsequent laboratory testing was not possible. However, correlation between the results of these tests and CPT results for other areas in the North Sea, allowed geotechnical properties to be inferred and to be used as the basis for the geotechnical design of the foundation. Assessment of the bearing capacity of the structure under hydrodynamic loading, as well as the resistance to sliding indicated that there maybe a risk of instability. As a consequence, a perimeter skirt was specified in order to reduce this risk. A discussion of the geotechnical issues considered during the design process is presented. Other design issues such as cyclic loading and penetration resistance in relation to a perimeter skirt, were considered and are commented on within this paper. The case history highlights some of the design problems faced by geotechnical engineers when designing structures for the offshore environment, and emphasizes the necessity for a comprehensive and, site specific, ground investigation, in order to facilitate the design process.
Department(s)
Civil, Architectural and Environmental Engineering
Meeting Name
6th Conference of the International Conference on Case Histories in Geotechnical Engineering
Publisher
Missouri University of Science and Technology
Document Version
Final Version
Rights
© 2008 Missouri University of Science and Technology, All rights reserved.
Creative Commons Licensing
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Document Type
Article - Conference proceedings
File Type
text
Language
English
Recommended Citation
Swift, Gareth, "Geotechnical Design of an Offshore Gravity Base Structure" (2008). International Conference on Case Histories in Geotechnical Engineering. 5.
https://scholarsmine.mst.edu/icchge/6icchge/session09/5
Geotechnical Design of an Offshore Gravity Base Structure
Arlington, Virginia
The paper focuses on the geotechnical design issues facing the design team responsible for the provision of an offshore Gravity Base Structure (GBS) to act as a clump weight for a Power Buoy located in the Lyell field of the northern North Sea, United Kingdom. The structure is to be positioned on the seabed, where ground conditions are considered variable but in general comprise of a surface layer of loose to very dense silty sand, underlain by a thick sequence of firm to very stiff sandy clay. Geotechnical data specific to the location of the GBS is limited; problems encountered during testing allowed only three cone penetration tests to be carried out to maximum depth of 12m and sampling for subsequent laboratory testing was not possible. However, correlation between the results of these tests and CPT results for other areas in the North Sea, allowed geotechnical properties to be inferred and to be used as the basis for the geotechnical design of the foundation. Assessment of the bearing capacity of the structure under hydrodynamic loading, as well as the resistance to sliding indicated that there maybe a risk of instability. As a consequence, a perimeter skirt was specified in order to reduce this risk. A discussion of the geotechnical issues considered during the design process is presented. Other design issues such as cyclic loading and penetration resistance in relation to a perimeter skirt, were considered and are commented on within this paper. The case history highlights some of the design problems faced by geotechnical engineers when designing structures for the offshore environment, and emphasizes the necessity for a comprehensive and, site specific, ground investigation, in order to facilitate the design process.
