Offshore structure and installation method

• US 5,383,748 A
• Filed: 08/20/1993
• Issued: 01/24/1995
• Est. Priority Date: 06/19/1991
• Status: Expired due to Fees

• Current Assignee: Kvaerner EARL and Wright
• Original Assignee: Kvaerner EARL and Wright
• Inventors: Waddell, John W.
• Primary Examiner(s): CORBIN, DAVID
• Application Number:
  US08/109,464
• Time in Patent Office: 522 Days
• Field of Search: 405/195.1, 405/203, 405/204, 405/211, 405/217, 405/224, 405/227, 405/228
• US Class Current: 405/217
• CPC Class Codes: E02B 17/0021 against ice-loads
• CPC Class Codes: E02B 17/02 placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto
• CPC Class Codes: E02B 2017/0086 Large footings connecting several legs or serving as a reservoir for the storage of oil or gas

Abstract

The invention provides an improved structure for standing offshore, particularly in arctic environments, and a method for installing this structure. The structure comprises a shield portion which rests on a seabed and primarily resists environmental loads, such as from ice, and a separate support portion which comprises a plurality of piles driven into the seabed to support a deck payload. The method for installing the structure comprises moving a shield portion of the structure to its intended location with piles pre-installed therein, setting the structure on the seabed, driving the piles into the seabed, and then severing any connection between the piles and the shield portion.

Claims

1. A method for installing a structure that stands offshore, the structure including a shield portion comprising a flat base having a first plan area, and a hollow leg having a second plan area smaller than said first plan area upstanding from a center of the base, the leg having a lower frustro conical part tapering upwardly from the base to an upper cylindrical part, in which the base rests on a seabed and is designed to resist lateral environmental loads primarily by friction forces generated by the weight of the shield bearing directly on the seabed, and in which said friction forces are supplemented by peripheral members on the base of the shield portion which project downwardly into the seabed to provide additional resistance to lateral environmental loads;

and a separate support portion which comprises a group of free standing deck payload support piles to support vertical loads imposed by a deck payload, in which the group of piles is wholly surrounded by the shield portion, the method including the steps of;

moving the shield portion of the structure to its intended location;

setting the structure on the seabed;

driving the deck payload support piles individually and independently into the seabed;

driving the peripheral members downwardly into the seabed; and

installing a permanent deck on top of the group of piles.

2. A structure for standing offshore and having a shield portion comprising a flat base having a first plan area, and a hollow leg having a second plan area smaller than said first plan area upstanding from a center of the base, the leg having a lower frustro conical part tapering upwardly from the base to an upper cylindrical part, in which the base rests on a seabed and is designed to resist lateral environmental loads primarily by friction forces generated by the weight of the shield bearing directly on the seabed, and in which said friction forces are supplemented by peripheral members on the base of the shield portion which project downwardly into the seabed to provide additional resistance to lateral environmental loads;

and a separate support portion which comprises a group of free standing deck payload support piles which are driven individually and independently into the seabed to support vertical loads imposed by a deck payload, in which the group of piles is wholly surrounded by the shield portion, and in which there is a permanent deck installed on top of the group of piles.

3. A structure as claimed in claim 2 wherein the deck support piles are pre-installed in the shield portion of the structure and there is provision for a pile driving hammer to be supported temporarily on the structure for driving the pre-installed deck support piles into the seabed.

4. A structure as claimed in claim 2, wherein the shield portion is of double skin construction, and after installation at least a portion of the space between the skins is filled with grout.