Troll Phase 1, design and execution of large scale rockdumping on a soft uneven seabed
- SINTEF, Trondheim (Norway)
- A/S Norske Shell, Bergen (Norway)
- Jebsens ACZ, Gorinchem (Netherlands)
Development of the Troll Phase 1 project required landfall, towards the onshore gas conditioning plant, of both 36-in. wet gas feed (or import) pipelines and 40-in. dry gas export pipelines. The plant is located on the Norwegian West coast characterized by a very uneven topography with rocky outcrops and depressions filled with very soft clay sediments. Landfall preparations comprised, besides the driving of a 3.5 km long subsea tunnel system, extensive preparations nearshore in the form of rockdumped supports to limit pipeline spanning. The geotechnical design of these large supports, up to 10.4 m in height, geometrically complex and on a sloping soft seabed, included extensive stability, settlement and soil consolidation analyses for functional and environmental (including earthquake) loads. The design was translated into detailed construction procedures and drawings by very effectively utilizing integrated 3D CAD modeling of seabed and supports. A total of 10 single pipeline supports and 22 combined supports with extensive counterfills were accurately placed, {+-} 20 cm vertically and {+-} 2 m horizontally, utilizing a free fall pipe system and state-of-the-art surveying technology. After pipelay the pipelines were covered at the major peaks to prevent uplifting during operations. Total volume of rock installed in the nearshore area was approximately 290,000 m{sup 3}. A further 66,000 m{sup 3} was installed over an area of 150 by 200 m (tie-in area) to support large spool pieces, connecting offshore and tunnel sections, and associated tie-in equipment. The article describes the geotechnical design, the construction engineering and the construction execution of the pre-lay supports and post-lay covers in the nearshore and tie-in area.
- OSTI ID:
- 400902
- Report Number(s):
- CONF-9606279--; ISBN 0-7918-1494-7
- Country of Publication:
- United States
- Language:
- English
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