SANTOS GLNG has today unveiled its tunnel boring machine and, in one of the project's final stages of construction, it will now begin earthmoving works under The Narrows crossing to Curtis Island.

Pipeline manager Greg Jones said the pipe would connect the 420km underground gas transmission pipeline from Maranoa.

"This is a complex process that will take around 12 months to complete and will involve the creation of an approximately 4.3km tunnel with a 3.4m internal diameter, and then placement of pipe," he said.

The second-hand, $6 million dollar machine is 100m long and 277 tonnes, and took a team of 12 people about six weeks to assemble.

Thiess tunnelling general manager Steve Wille said the tunnel boring machine was a precision tool on a large-scale.

"The machine cuts and removes the soil and rock, then lines the tunnel with pre-cast concrete segments in a remarkably seamless operation," Mr Wille said.

Once the tunnel has been constructed, the tunnel will be flooded with sea water and the pipe will be floated and pulled through.

Mr Jones said the development of the transmission pipeline was progressing well as the project worked towards first exports of LNG in 2015.

"We have now buried 60km of pipe in Arcadia Valley, and along the pipeline route almost 170km has been cleared and graded, and 120km of pipe has been welded," Mr Jones said.

"Rehabilitation work has started in Arcadia Valley which involves reinstating topsoil, sowing grass seeds and establishing pasture back on disturbed areas.

"We are working along the pipeline route, and undertaking clearing, grading and stringing work in the Banana Shire area in anticipation of pipe burial in coming months.

"Clearing and grading work in the Central Highlands area has also commenced."

The Santos GLNG Project is a joint venture between Santos and three of the world's largest energy companies, PETRONAS, Total and KOGAS.

A team of 12 people worked for about six weeks to assemble a 100m long, 277 tonne tunnel boring machine on-site for Santos GLNG.
A team of 12 people worked for about six weeks to assemble a 100m long, 277 tonne tunnel boring machine on-site for Santos GLNG. Emily Kemp

The pipeline will carry coal seam gas from the Surat and Bowen basins to Curtis Island. From there, the gas will be liquefied for export.

When finished, it will be the third CSG pipeline to Curtis Island from the mainland.

QGC and APLNG completed similar projects in February but, unlike the Santos tunnel, those pipelines were laid in sub-sea trenches.

Mr Jones said Santos GLNG has found the under-harbour option more feasible.

"When we looked at it, from a technical, environmental, safety and obviously a cost point of view, and unlike the other two projects who came to the conclusion of trenching, we came to the conclusion that tunneling made more sense," he said.

"It was a bit of the off the wall approach. It is not common. I don't know what numbers, figures they used, but we just came to that conclusion."

He said a priority had been to minimise environmental impact.

"By going under, we're not dredging. We're not excavating the foreshore."

Saipem project manager Alessio Testa said it had been a mammoth effort getting to the day the tunnel boring machine was unveiled.

"Every time I arrive here and even today, looking around. I'm lost. I cannot help but to be amazed at the works (done so far)," he said.

"Remembering the joy of this moment, we will be able to tackle and overtake the challenges ahead of us."