Method for installing at least one mooring line of a floating installation in a body of water and associated floating installation
The method comprises installing at least one lower section of a mooring line at the bottom of the body of water; trapping the lower section in the ground; connecting an upper unit of the floating installation to the mooring line. The lower section being constituted by a chain, the chain defining, after the connection of the upper unit, a lower end of the mooring line not provided with a mooring point pre-mounted on the mooring line, in particular an anchor or pile.
1 . A method of placing at least one mooring line of a floating installation in a body of water, the method comprising:
installing at least one lower section of a mooring line in a ground at a bottom of the body of water;
trapping the at least one lower section in the ground;
coupling an upper unit of the floating installation to the mooring line;
the at least one lower section of the mooring line consisting of a chain, the chain delimiting, after the coupling of the upper unit, a lower end of the mooring line devoid of mooring point pre-mounted on the mooring line,
wherein trapping the at least one lower section in the ground includes placing the at least one lower section in the ground over a depth and/or a length chosen such that after coupling the upper unit to the mooring line, at least the tension applied to the lower end of the mooring line is zero, and
wherein a chain length of the lower section is calculated prior to installation by simulating a tension extending along the chain, as a function of the upper assembly, a depth of the lower end in the ground, a value of the tension at the lower end, and a direction of the lower section at ground level.
2 . The method according to claim 1 , wherein trapping the at least one lower section in the ground comprises pulling the at last one lower section to move the at least one lower section from a first penetrating configuration to a second trapping configuration.
3 . The method according to claim 2 , wherein the first penetrating configuration is linear, the second trapping configuration being in the form of a catenary.
4 . The method according to claim 1 , wherein the at least one lower section is provided with at least one connector, coupling the upper unit to the mooring line comprising connecting an upper section of the mooring line to the at least one connector and tensioning the upper section from the upper unit or from an installation vessel.
5 . The method according to claim 1 , wherein trapping the at least one lower section in the ground comprises jointly lowering into the ground a caisson and the at least one lower section, the method further comprising separating the caisson from the at least one lower section, then raising the caisson out of the ground, the at least one lower section remaining in the ground.
6 . The method according to claim 5 , wherein the joint lowering into the ground of the caisson and of the at least one lower section takes place along a vertical or substantially vertical axis.
7 . The method according to any of claim 6 , wherein the caisson defines at least one longitudinal channel in the external surface thereof, the at least one lower section being located in the longitudinal channel during the joint lowering into the ground of the caisson and of the at least one lower section.
8 . The method according to claim 6 , wherein separating the caisson from the at least one lower section comprises lowering a length of chain from the at least one lower section under the caisson to form an accumulation of chain under the caisson, the accumulation of chain delimiting the lower end.
9 . The method according to claim 6 , comprising casting a sealing compound and solidifying the sealing compound under the caisson after the joint lowering into the ground of the caisson and of the at least one lower section or/and placing additional sedimentary material, instead of the volume occupied by the caisson after raising the caisson out of the ground.
10 . The method according to claim 6 , wherein the joint lowering into the ground of the caisson and of the at least one lower section comprises spraying a liquid under pressure under the caisson.
11 . The method according to claim 6 , wherein the joint lowering into the ground of the caisson and of the at least one lower section comprises injecting a gas or a fluid into the caisson and/or around the caisson, to lift solids excavated by the caisson.
12 . The method according to claim 6 , comprising installing a plurality of lower sections of a plurality of mooring lines in the ground, the lower sections of at least two mooring lines being lowered together with the same caisson.
13 . The method according to claim 1 , wherein installing at least one lower section of a mooring line in a ground comprises placing a chain in a horizontal trench in the ground, trapping the lower section, the trapping of the lower section including pulling at least one end of the chain to move the chain from a first linear configuration to a second configuration different from the first configuration and connecting at least one end of the chain to an upper section of the mooring line coupled to the upper unit.
14 . The method according to claim 13 , wherein the chain has two ends, the method comprising pulling the two ends of the chain to form two lower sections of two respective mooring lines trapped in the ground, the mooring lines having a common lower end, the method comprising connecting each end of the chain to an upper section of a respective mooring line coupled to the upper unit, or to another upper unit.
15 . The method according to claim 13 , wherein the second configuration is a curved configuration.
16 . The method according to claim 1 , wherein the lower end of the mooring line is devoid of an anchor or of a pile.
17 . A floating installation in a body of water, comprising:
an upper unit and at least one mooring line coupled to the upper unit, the mooring line including an upper section operatively connected to the installation and a lower section coupled to the upper section via a connector configured to rest on the bottom of a body of water, wherein the lower section is penetrating and trapped in the ground at the bottom of the body of water;
the lower section of the mooring line consisting of a chain, the chain delimiting, after the coupling of the upper unit, a lower end of the mooring line devoid of mooring point pre-mounted on the mooring line,
wherein with the lower section trapped, the lower section extends in the form of a catenary between the lower end of the chain and the connector.
18 . The installation of claim 17 , wherein a tangent to the lower section catenary section is vertical or inclined by less than 30° with respect to the vertical.
19 . A method of placing at least one mooring line of a floating installation in a body of water, the method comprising:
installing at least one lower section of a mooring line in a ground at a bottom of the body of water, the lower section of the mooring line coupled to an upper section of the mooring line via a connector;
trapping the at least one lower section in the ground by applying traction to the connector to move the lower section into a catenary while the lower section remains in the ground;
coupling an upper unit of the floating installation to the mooring line via the connector,
the at least one lower section of the mooring line consisting of a chain, the chain delimiting, after the coupling of the upper unit, a lower end of the mooring line devoid of mooring point pre-mounted on the mooring line,
wherein the lower section is configured such that friction between the lower section and sediment present in the ground and a weight of the sediment located above the lower section resists and overcomes traction forces applied to the connector thereby trapping the lower section in the ground.