Seabed base structure and method for installation of same
This publication relates to a shallow water terminal, preferably for storing and loading or unloading hydrocarbons, such as LNG, oil or gas. The base structure comprises a floatable, and removable seabed substructure ( 10 ) intended to be supported by a seabed ( 30 ), the seabed substructure ( 10 ) comprising a base structure ( 11 ) provided preferably with an upwards extending wall structure ( 22 ), arranged along at least a part of the periphery of the base structure ( 11 ), the base structure ( 10 ) preferably also being provided with an opening ( 23 ) in the wall structure ( 22 ) for allowing the floatable module to be berthed in and supported by the seabed substructure ( 10 ). The base structure ( 10 ) is provided with strong points ( 24 ) configured to receive the ends of preinstalled vertical piles ( 14 ) for at least temporary support of the base structure ( 11 ) during a piling operation for permanent piling of the base structure ( 10 ) to the sea bed ( 30 ). The publication also relates to a method for piling a base structure on or above a seabed ( 30 ).
1. A floatable and removable seabed base structure ( 10 ) for storing and loading or unloading hydrocarbons and intended to be supported by a seabed ( 30 ), the seabed base structure ( 10 ) comprising a beam structure ( 11 ) provided with an upwards extending wall structure ( 22 ) arranged along at least a part of the periphery of the seabed base structure ( 10 ),
the seabed base structure ( 10 ) having an opening ( 23 ) in the upwards extending wall structure ( 22 ) for allowing a floatable module to be berthed in and supported by the seabed base structure ( 10 ),
the seabed base structure ( 10 ) having a plurality of strong points ( 24 ) each configured to receive the end of a preinstalled vertical pile ( 14 ) for at least temporary support of the seabed base structure ( 10 ) during a piling operation for permanent piling of the seabed base structure ( 10 ) to the sea bed ( 30 ),
the plurality of strong points ( 24 ) extending laterally outwards from the upwards extending wall structure ( 22 ), wherein the plurality of strong points ( 24 ) are arranged spaced apart from one another longitudinally across a length of the upwards extending wall structure ( 22 ) and away from adjacent corners of the upwards extending wall structure ( 22 ).
2. The seabed base structure ( 10 ) according to claim 1 , wherein the plurality of strong points ( 24 ) are positioned above sea level ( 29 ).
3. The seabed base structure ( 10 ) according to claim 1 , wherein the plurality of strong points ( 24 ) are positioned below sea level ( 29 ).
4. The seabed base structure ( 10 ) according to claim 1 , wherein the plurality of strong points ( 24 ) are arranged on a lower side of beams, cantilevers or sleeves or ducts extending laterally out from the upwards extending wall structure ( 22 ).
5. The seabed base structure ( 10 ) according to claim 1 , wherein the plurality of strong points ( 24 ) are each provided with a releasable locking device for temporarily locking an upper part of the preinstalled vertical pile ( 14 ) in a fixed position.
6. The seabed base structure ( 10 ) according to claim 1 , wherein the upwards extending wall structure ( 22 ) is an integrated part of the seabed base structure ( 10 ) and the plurality of strong points ( 24 ) form an integrated part of the upwards extending wall structure ( 22 ).
7. The floatable and removable seabed base structure ( 10 ) according to claim 1 , wherein each strong point ( 24 ) comprises a recess dimensioned to encircle along a circumference of the end of the received preinstalled vertical pile ( 14 ).
8. The floatable and removable seabed base structure ( 10 ) according to claim 1 , wherein the plurality of strong points ( 24 ) are each arranged on an underside of a cantilever extending laterally outwards from the upwards extending wall structure ( 22 ).
9. A method for installing a seabed base structure ( 10 ) according to claim 1 on a seabed ( 30 ),
the method comprising driving at least two rows ( 13 , 13 ′) of temporary piles ( 14 ) into the seabed ( 30 ), the distance between each of the at least two rows ( 13 , 13 ′) and the distance between adjacent temporary piles ( 14 ) in each row ( 13 , 13 ′) corresponding with a location of purpose built strong points ( 24 ) on the seabed base structure ( 10 ), towing the seabed base structure ( 10 ) between the at least two rows ( 13 , 13 ′) of temporary piles ( 14 ) and bringing it to a position in which each of the purpose built strong points ( 24 ) are vertically aligned with a corresponding temporary pile ( 14 ) upper end, ballasting the seabed base structure ( 10 ) to rest stably on the temporary piles ( 14 ), and piling the seabed base structure ( 10 ) permanently to the seabed ( 30 ).
10. The method according to claim 9 , wherein the seabed base structure ( 10 ) is piled to the sea bed ( 30 ) using a number of permanent piles driven into the seabed ( 30 ), a top of each permanent pile being rigidly fixed to the seabed base structure ( 10 ).
11. The method according to claim 9 , further comprising removing the temporary piles ( 14 ) supporting the seabed base structure ( 10 ) stably and rigidly during the pile operation upon completion of permanent piling of the seabed base structure ( 10 ).
12. The method according to claim 11 , wherein the temporary piles ( 14 ) are removed by cutting off the temporary piles ( 14 ) at a level of the seabed ( 30 ).
13. The method according to claim 9 , wherein the seabed base structure ( 10 ) is provided with ballast tanks, using water to adjust weight and buoyancy and the vertical forces and load exposures acting on the temporary piles ( 14 ) during installation of the seabed base structure ( 10 ).