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Thiess completes tunnelling to Curtis Island

LNG Industry,

Thiess has delivered a major milestone for Saipem Australia, the principal contractor for the Santos GLNG Gas Transmission Pipeline Project, by successfully tunnelling under ‘The Narrows’ off Gladstone to connect Curtis Island with the mainland.

The 4.3 km underwater tunnel has provided a conduit for installation of the pipeline without disturbing the marine environment.

Tunnel boring machine

Tunnelling commenced in April 2013 and the 100 m long, 277-ton tunnel boring machine (TBM) has been in operation 24/7 on its journey to the tunnel reception shaft on Curtis Island.

Named Rose-Ella by the children at the local Rosella Park State School, the 4 m diameter TBM also lined the tunnel by installing over 21 750 pre-cast concrete segments. A cement-based grout was injected behind the segment lining to permanently seal the tunnel, which has a finished internal diameter of 3.4 m.

In early February, the TBM broke through to Curtis Island in front of representatives from Thiess, Saipem Australia and Santos GLNG who had gathered to witness the achievement.

Gas pipeline route

The tunnel forms part of Santos GLNG’s 420 km gas pipeline route from its gasfields around Roma and Fairview to the gas liquefaction plant currently under construction on Curtis Island.

Thiess Managing Director, Bruce Munro, commented: “The Narrows Crossing has been a model of collaboration and Thiess is delighted to have applied its tunnelling expertise to such a significant project”.

Commenting on the workforce, Thiess’ General Manager Tunnelling, Steve Wille, said: “I can’t speak highly enough of the team and what they’ve achieved, particularly in the last couple of months when the geotechnical conditions got very tough”.

Complex repair process

Tunnelling had to stop for a few weeks mid-journey for the crew to repair the cutter-head. To access the cutter-head, 2.4 bar of compressed air pressure was required to prevent soil and water ingress, involving a complex process. This meant repair crews had to go through compression and de-compression, similar to that required for divers.

“It can’t be understated how difficult the conditions were for those guys and I’m extremely proud of the way they fixed the cutter-head and brought the machine home,” Wille explained.

Huge operation

The tunnelling operation has employed a team of 75 people and required a total of more than 420 000 man-hours to complete.

The TBM excavated approximately 55 000 m3 of earth which is being used by the Gladstone Regional Council to rehabilitate an ash pond associated with a coal fired power station.

The completed tunnel is now being stripped of services and thoroughly cleaned. It will then be flooded to provide buoyancy for the pipeline, which will be installed by Saipem Australia.

The video of the historic moment can be viewed here.

Adapted from press release by Katie Woodward

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