$3500 a m timber pipeline replaces worlds’ biggest soaker hose

Built of King Billy Pine in 1938, the pipeline was originally operated by Mt Lyell Mining, to supply electricity to its copper-mining operations in Queenstown. Now owned by Hydro Tasmania, the 71-year-old pipeline had reached the end of its effective life, having sprung so many geyser-like leaks that it was dubbed ‘the world’s biggest soaker hose.’
So Tasmanian company Hazell Bros, is executing a complex $7.7m design-and-construct project, officially called the Lake Margaret Pipeline Reconstruction Project. Lake Margaret lies in an area of abundant rainfall, about 20 minutes north of Queenstown on Tasmania’s rugged west coast. Once completed, the new pipeline will convey water to the Lake Margaret Upper Power Station, which will be refurbished by Hydro Tasmania as part of the project.
It didn’t take long for project manager Aaron George and his peak-construction team of 25 – a combination of Hazell Bros staff and local labour – to discover just how much rain falls in the region. “Lake Margaret actually had the dubious distinction of being the wettest place in the southern hemisphere for September 2008, which is when we commenced the construction phase,” George says.
They knew this unusual project would come with its own set of challenges, and weather was just one of them (it also snows in winter). Wildlife was another: “We had snakes in summer – the place is teeming with them - leeches in winter, and in between we dealt with March flies,” says George.
The initial stages of construction involved demolishing the existing 1200mm diameter, 2.2km-long wood-stave pipeline and steel supports, and removing them from site. “The pipeline was fully drained when we came to demolish it,” says George. “Being timber, they expected it to dry out and then just fall apart. It dried out, but it didn’t fall apart, it was still a very rigid structure.”
Trolley rescue
The next steps were the survey and construction of new concrete footings along the alignment, the supply and installation of galvanised structural support steelwork for the new pipeline, and building and commissioning the motorised access trolley system Hydro Tasmania wanted in order to perform inspections and maintenance. “As far as we can ascertain, no other pipeline in the world has a motorised trolley on it,” says George. “We Googled it pretty hard, but at this stage it appears to be a one off. So with no existing system to model ours on, it involved quite a major design process requiring innovative engineering. Safety was a major consideration too.”
As it happened, Hydro’s requirement for the trolley system proved to be a boon for construction. “One of the biggest issues we were dealing with at the time of tendering and during the design phase was how to build this pipeline safely and efficiently,” says George. The location and terrain meant standard construction methods such as scaffolding were not the most efficient, he said. “The pipeline essentially sits on the edge of a hillside. You have a couple of metres on either side of you, and then the sheer cliff face. There isn’t much room to manoeuvre and do the work; or to place materials.
“Everything had to be fairly carefully staged and thought through before we put materials on site. This led to our decision to design the trolleys so they could be utilised in construction: to help build the pipeline in locations where it’s off the ground – in some places it’s 5m above the ground – and to assist us in placing the pipeline support structural steel work. It’s worked very well.”
Three trolleys were built in-house. Powered by diesel motors that drive hydraulic wheels, the 5m long trolleys straddle the pipeline in a series of A-frame structures. Continuous beams at the bottom of the trolley on either side of the pipeline run along the steelwork that supports the pipe. Platforms on both sides of the trolley allow people to stand next to the pipeline on either side of it.
It became clear early in the design phase that the more effort put into the design, then the more the design details were tweaked to provide greater construction time efficiencies. “As an example, with the structural steel components, we had to make it a bit like a Lego set on site. Because we don’t have normal access for cranes to erect the steelwork, it was essential that everything had to be able to be manhandled.”
Designers Johnstone McGee and Gandy (JMG) assisted Hazell Bros with the design component. “JMG understood our requirements and, being familiar with the site location, were thus able to provide us with a very efficient pipeline support structure and motorised trolley unit design,” says George.
The only other major subcontractors on the project were the structural steel fabricators. “We chose Queenstown-based company Schulze Engineering. “We also used one of our regular fabricators, Maintenance Welding from Launceston, because it was such a large job.”
Timber choice
Alaskan Yellow Cedar was the timber chosen to rebuild the pipeline. “Hydro Tasmania considered using King Billy Pine, but the availability, the quantities needed and the cost put it out of the running,” says George. “So they looked around the world for suitable wood-stave companies that supply this timber, and chose International Tank and Pipe Company (ITP) from Portland Oregon.”
With a 40-year design life, the cedar is expected to have durability similar to King Billy Pine.
ITP undertook all the preparation of the timber in the US. It was kiln dried in ITP’s yards and then machined to its right profile. From there it was packed into bundles and shipped by container to Australia. Each bundle contained 44 pieces; as 43 pieces are required to make a full round on the pipe, there was little margin for error. In common with other materials, the timber was delivered to the site by helicopter.
“The preparation is very exacting, but ITP has gained extensive experience through its 100-plus year’s existence,” says George. “However, they haven’t recently done a pipeline without a road next to it to facilitate construction. So the challenge wasn’t so much about building a wooden pipeline, it was more how to build it without normal access for plant and equipment. And that’s how the trolley system came online: to get materials to worksites and to give us efficient work methods.”
A wood-stave supervisor from ITP remained on site throughout the construction. “His job was to instruct Hazell Bros on how to build this pipeline. Because a timber pipeline hasn’t been built in Australia for a very long time, the necessary skills are non-existent – certainly in Tasmania.”
They expect to complete the construction of the pipeline in early August. “From there we fill it and go into the commissioning phase, fixing potential leaks as the timber takes up under saturation. ITP will be on site to provide us with additional guidance during the commissioning phase.”
The unusual, challenging and innovative nature of the project has made it a very satisfying one to work on. “We’ve enjoyed it because it’s probably something we’ll never get to do again,” says George. “The project is unique and everyone involved has really taken ownership of it. There aren’t too many projects where people come up to you and say ‘I was thinking about a way to improve productivity; maybe it would be a bit quicker if we do this.’”
He adds that he’s been exceptionally lucky to have this particular crew on the job. “It’s all well and good for me to sit in an office doing the project management role, but those guys are out there in the snow and the rain and the hail applying themselves so diligently to building it. Hats off to them.”