From the magazine

A new frontier in HDD

The Tasmanian Gas Pipeline (TGP) is the natural gas transmission pipeline which transports gas from Longford in Victoria to Tasmania. The 734 km subsea and onshore pipeline was commissioned in 2002.

Today, the pipeline and associated assets are managed and operated by Tas Gas Networks on behalf of owner TGP.

The pipeline provides the only supply of natural gas to Tasmania, and since it was commissioned in 2002 has provided Tasmanians with an alternative to hydro-generated electricity.

Construction of the Pipeline

Following rigorous engineering, environmental and heritage surveys and studies and pending approvals, construction of the TGP began in 2001.

The $A350 million project featured 430 km of onshore pipeline, a 305 km pipeline across Bass Strait and conversion of the Bell Bay Power Station to a gas-fired facility.

The benefits of bringing natural gas to Tasmania were many. With the state’s hydro-powered resources at capacity, natural gas would provide private and commercial users with an alternative, economical resource which would reduce costs, encourage the expansion of existing businesses and spur investment in new industries which use gas.

The pipeline’s planned route would see it cross under the Tamar River, near Bell Bay, and continue to Rosevale, near Launceston. It was here that Trenchless Technology was employed to achieve the best environmental outcomes for the region, and the project.

Trenchless Technology shines

It was decided that the best way for the pipeline to cross the Tamar River would be underneath it, with horizontal directional drilling (HDD) to be utilised to clear a path for the pipeline.

Drilling on what was one of the world’s longest under river drilled crossings began in late February on the east side of the Tamar River, near the Bell Bay Power Station.

The 2,046 m curved, underground drill hole punched through the ground at Rowella, on the west bank of the Tamar River, at around 5 am on Friday 22 March 2002. The drill rig used at the Tamar River had a pull-back capacity of 300 tonnes and the curved drill hole reached 86 metres beneath the bed of the river.

Innovative technique

A further 11 rivers in northern Tasmania were then crossed using a horizontal directional drill. At the time, this environmentally-friendly drilling technique had been used regularly in the pipeline industry to tunnel underneath major rivers and sand dunes without disturbing the above ground environment.

The drills were undertaken by construction contractor McConnell Dowell, who sub-contracted the river drills to joint venture partners, Stockton (a drilling company owned by McConnell Dowell) and Lucas, Australia’s largest directional drilling company.

Duke Energy International’s TGP Project Manager Carl Fisher said that the successful “÷punch-through’ of the Tamar River was greeted with great excitement by Duke Energy and the pipeline industry.

“The Tamar River crossing has been a terrific achievement for many reasons,” Carl said. “Not only does this represent a record in Australia for its length, but the work was completed in excellent time.

“Stockton Lucas set an outstanding pace, completing 12 major underground river crossings in just seven weeks using four drill rigs.”

Major works

Following these drills, construction of the TGP continued. At the time of printing this article, approximately 170 km of pipe had been laid on the bed of Bass Strait, and more than 60 km had been buried onshore in Tasmania, representing approximately 30 per cent of the TGP.

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