Centrifuge modelling of 3-leg jackups with non-skirted and skirted spuds on partially drained sand
- Cambridge Univ. (United Kingdom). Engineering Dept.
This paper presents and compares results from two centrifuge experiments modelling the cyclic load-displacement and pore-pressure responses for a small 3-leg prototype jackup on a medium-dense quartz sand layer. Flat spuds were used in the first test. Flat spuds lifted with short vertical skirts were used in the second test. The data showed extremely high foundation fixities for both types of spud. In the context of these very high values, and in the absence of scour, overall dynamic fixity was slightly reduced by the presence of skirts. Generally the skirted spuds settled less than the non-skirted spuds. In extreme events the greater pullout capacity of the skirted foundations was confirmed. Positive and negative pore pressure excursions were not symmetric. High suctions occurred in parts of cycles. Pore pressure dissipation times also depended on load magnitude, indicating different patterns of pore pressure generation for different loads. There was no evidence of cumulative pore pressure buildup. Considerable work remains to validate and generalize these results. Care is needed in extrapolating the data to larger rigs, to rigs with different relative height-to-leg spacing ratios or different prototype spud diameters, or to rigs on sands with different fundamental properties (such as calcareous sands), or sands with different densities, non-uniformity, or layering. Nevertheless the data support the proposition of benefits available from the use of skirts for jackup footings. 34 refs.
- OSTI ID:
- 160733
- Report Number(s):
- CONF-950501-; TRN: IM9603%%315
- Resource Relation:
- Conference: 27. offshore technology conference, Houston, TX (United States), 1-4 May 1995; Other Information: PBD: 1995; Related Information: Is Part Of 27. Annual Offshore Technology Conference: 1995 Proceedings. Volume 3: Construction and installation/field drilling and development systems; PB: 591 p.
- Country of Publication:
- United States
- Language:
- English
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