Gorgon Project – LNG Jetty and Marine Structures
Barrow Island, Western Australia
The heavy lift facility (HLF) at Barrow Island comprises 25, 12.5m diameter concrete caissons. These units were transported to site and installed using a heavy lift vessel.
Madsen Giersing (MG) was appointed by Saipem Leighton Consortium to provide the detail design and technical support services for the design of the lifting arrangement and load spreading frames required for the caisson installation.
The preassembled caissons consisted of 5 or 6 precast concrete rings (with a total weight of up to 725T). These were tied together with 54 high tensile bars. The main project challenge was to develop a lifting arrangement that ensured no cracks were induced in the caisson during the lifting operation.
MG developed the lifting arrangement utilising 24 of the caisson tie bars. This allowed the stress within the caisson tie bars to remain low enough so as not to induce cracking in the concrete rings.
The lifting arrangement comprised 6 individual lifting beams, each connected to 4 tie bars. These beams were connected to a 6 point lifting frame via a grommet sling. Three
slings were attached to the lifting frame and connected to a 1000T shackle on the hook. This allowed for a relatively equal load distribution on the 6 lifting points.
This system allowed the client to preassemble the units off-site and transport and install on-site, which reduced the time taken to construct the facility. The caissons were installed in position at a rate of 1 caisson per day.
The Gorgon Project is operated by an Australian subsidiary of Chevron and is a joint venture of the Australian subsidiaries of Chevron (47.3 percent), ExxonMobil (25 percent), Shell (25 percent), Osaka Gas (1.25 percent), Tokyo Gas (1 percent) and Chubu Electric Power (0.417 percent).