GB1512025A - Gravity platform and a method used in its construction - Google Patents

Abstract

1512025 Offshore structures; gravity platforms BOUYGUES SA 2 June 1975 [25 June 1974] 23808/75 Heading E1H A gravity platform comprises a deck 2 which is supported by a plurality of vertical reinforced concrete columns P and a base I which includes two walls 5, 6 defining an annular space in which lower cylindrical portions 7 of the support columns P and further reinforced concrete columns A are located, the lower cylinder portions of the columns being integrally formed with the walls 5, 6. The platform is built by first constructing a lower portion of the base comprising a horizontal slab 3 externally of the portions 7 and extending between the portions 7 and the walls 5, 6, lower parts of the walls 5, 6 and cylinder portions 7 in a dry dock and then floating out this lower portion of the base for subsequent completion afloat. Alternatively sections of this lower base portion are built separately in a dry dock and then progressively connected together afloat. The base is completed afloat by further casting concrete and then frusto portions 9, 10 of the support columns P and frusto conical portion 12 and upper portion 11 of the further columns A are built onto the floating base 1. The further columns A are sealed at their upper ends and carry floatation collars 19. The deck 2 is built in a dry dock and has upper portions 18 of the support columns P subsequently fixed temporarily in passages 14. The base 1 is submerged and the deck 2 is located above it so that the support column portions 10, 18 can be permanently connected together. The deck 2 is moved relative to the column portions 18 by either submerging the base 1 further or raising the deck 2 and, when in the desired position, it is then permanently connected to the columns P.