McConnell Dowell Project Manager Paul Thomas and I stand atop the Bogong high plains, looking over the vast rippled surface of the 28,000 megalitre capacity Rocky Valley Reservoir.

This is the storage reservoir for the water that powers the entire hydro scheme, currently made up of a sequence of three existing power stations that descend from Falls Creek and down the Kiewa Valley, in the Bogong region of Victoria’s Alpine National Park.

Owned by AGL Southern Hydro, the scheme was built over a period of more than 20 years, commencing in the late 1930s and, after construction works were interrupted by World War II, completed in 1961.

It was a sunny 25 degrees Celsius in Wodonga earlier that day. Now at 1,600 metres, the air is decidedly chilly. Paul is showing me around the entire hydro scheme, starting from the heights of the reservoir and concluding with an up close look at the tunnel boring machine (TBM) as it drills the last metres of the rock in the main headrace tunnel.

From these heights, water stored in the Rocky Valley Reservoir and the nearby Pretty Valley Reservoir flows to the MacKay Creek Power Station via tunnels and penstock. From MacKay Creek, it currently flows down the Pretty Valley Creek to Junction Dam, then through Clover Power Station and onto the West Kiewa Power Station.

The Bogong project will harness the water supply already used by the existing three power stations to produce additional power for periods of high demand, by diverting flow from the McKay Creek Power Station at peak times via a 7 km tunnel running under the mountains of the National Park, and connecting to the newly constructed Bogong Power Station, positioned adjacent to Junction Dam.

After first conceiving the project in 2000, AGL Southern Hydro awarded a $A160 million contract to McConnell Dowell for the design and construction of a new tunnel connecting the McKay Creek Power Station with the proposed Bogong Power Station, along with the associated infrastructure.

As we drive down the mountain from the Rocky Valley Reservoir to the Clover Power Station, Paul explains why MacDow was the successful tenderer for the job.

“Basically it came down to the most cost-effective solution. MacDow has a very good history with TBMs. The company was formed in 1960, and has not only worked in tunnels but also pipelines, civils, electrical works, so it’s a multi-discipline contractor. And in terms of TBM, they’ve done tunnelling work in Singapore previously, in New Zealand, and also some major projects here in Australia, so they’ve got a very good track history of difficult and challenging tunnelling jobs. In other words, the jobs that other contractors won’t touch.”

Indeed, MacDow established a reputation as a leader in tunnelling during the mid-1990s, setting three world records for TBM tunnelling rates during drilling operations at the Blue Mountains Sewerage Transfer Scheme. Completed 17 months ahead of schedule, the project drilling records included 70.5 m in a single eight-hour shift, 172.4 m in a single day and 703.3 m in a single week.

“Certainly from a hydro point of view, time is of the essence. There’s always going to be time constraints, always pushing harder to get it finished earlier,” says Paul as he navigates the ute down the winding Bogong High Plains Road.

The company proved its capacity to work within tight timeframes when it successfully completed the Eastern Distributor Tunnels for the opening of the Sydney 2000 Olympics. The very tight construction program meant that the workforce was organised into a 24 hour day roster, working 7 days a week. The tunnels were completed one month early. Value engineering

Design optimisation is also a strength for the company. As we pass the McKay Creek Power Station, Paul tells me how elements of the design were improved to achieve the most cost-effective outcome.

By undertaking hydrojacking tests and onsite coring tests, the length of the High Pressure Head Race Tunnel steel liner was reduced from 950 m to 700 m. In addition, the diameter was reduced from 3.4 m to 3 m, without compromising any hydraulic requirements. This resulted in significant cost savings for AGL Southern Hydro.

“Originally it was all steel liner, and that’s to do with some of the pressures that builds up when the water is going into the tunnel, to stop it exploding, literally – that’s why the steel lining was used. But when we checked the stresses in the rock, we found we didn’t need such a robust steel lining section. We could replace that with concrete. So there was a bit of a cost saving scheme, about 400 m of concrete, and then 700 m of steel liner.”

Other design optimisations included increasing the alignment on the main tunnel from two per cent to four per cent, which resulted in a shorter depth of the head pond drop shaft.

“In hindsight, this is quite steep because we did have some problems with our locomotive capacity. We’ve got locomotives which are about 15 tonne capacity, but the steepness of the gradient meant that they weren’t efficient and sometimes couldn’t get up the tunnel.”

While this challenge wasn’t anticipated, it was quickly solved by lessening loads, using larger capacity locomotives, and introducing more rigorous maintenance on the rail tracks.

For MacDow, winning the contract was an important step in getting a foothold in the hydro market, given the growing importance of environmentally sustainable operations, and the increase in demand for renewable energy sources.

“For McConnell Dowell to have this almost as a signature project, so to speak, it’s very important for us as a company.” Community support

The local community has shown great support for the project, with regular meetings with local stakeholders, visits by the rotary club and progress reports made by local schools.

“There’s a lot of interest in this TBM machine, which was actually named by some school children in a competition. One of the very bright school kids, in my opinion, came up with Aurora Australis – which I think is fantastic, it’s probably one of the best TBM names I’ve ever heard,” says Paul.

The name Aurora Australis, refers to southern polar lights, and captures the idea that the new tunnel and power station will bring light to the region through hydro electricity.

Even before the project's is commissioning, the local community has seen an improvement to its roads after rock from the tunnelling spoil was used in the sealing of the road from Falls Creek to Omeo. Challenges

One of the main challenges encountered during the project was the variable geological conditions, ranging from ’massive’ rock with Q values in excess of 100 to highly fractured rock with Q values of less than 0.1.

The main waterway for the Bogong project was constructed largely within the East Kiewa Granodiorte, a plutonic igneous rock, formed by an intrusion of quartz-rich magma, which cools in batholiths below the Earth’s surface.

While extensive geological and geotechnical testing was conducted prior to the project’s commencement, during drilling operations the rock was found to be harder than originally anticipated.

“We had advanced the tunnel, and the rock itself was harder than originally anticipated. The average strength is in excess of 180 MPa, which makes it five or six times stronger than the concrete in that structure,” explains Paul, pointing to the solid concrete shell of the newly constructed power station.

“It’s very similar to granite, in composition, and it’s very massive, which means there are very few joints, which means it’s very difficult to mine on occasions.”

At one point during excavation of the main headrace tunnel, operations had to stop because the rock was self-mining, meaning the TBM couldn’t be advanced at all. While this resulted in significant delays and required additional ground support, the project is still on schedule to be finished ahead of the December 2009 contract timeframe.

The Aurora Australis TBM

A 5 m diameter Robbins TBM was chosen to excavate the 800 m headrace access tunnel and 5,700 m main headrace tunnel. Refurbished by Herrenknecht in Germany, the machine had completed two previous projects in Europe, the last being a water tunnel in Lugano, Switzerland.

As we climb into a caged locomotive to begin our 30 minute, 6 kilometre journey into the main tunnel, Paul explains that the TBM is a single gripper, main beam hard rock machine, allowing it to grip against the side walls of the excavated tunnel and propel itself forward using four no. hydraulic propulsion cylinders connected to the main beam.

The combined force of these cylinders is approximately 1,000 tonnes. The rotating cutter head is connected to the main beam and a series of six no. frequency controlled electric motors producing 1,800 kilowatts. The scale of this force becomes more and more apparent as we advance through the almost pitch black tunnel – while there is not much to see, the noise is almost deafening.

The cutter head is made up of 33 x 19 inch cutters, which are front loading, and require special maintenance procedures.

“As these are front loading cutters, we can’t change the cutters from inside the machine. We have to pull the machine back slightly, so there’s a gap between the machine and rock, and our workers have to go in there to change the cutters. So you can imagine that’s quite a difficult job in itself. So we’ve got very specific procedures on checking that area. The people that are going in there are skilled, they know what they’re doing. But more importantly making sure the conditions for them to go into that gap are 100 per cent safe,” Paul had explained earlier in the day.

The maximum cutter head thrust is 10,395 kN and maximum head rotation is 10.9 rpm. One stroke of the TBM is 1,800 mm, and in anticipated conditions this takes approximately 40 minutes. The machine is also equipped with a probe drill with a range of 360 degrees and two no. roof bolting hydraulic rock drills for the installation of rock bolts.

The TBM measures approximately 30 metres in length, but our locomotive stops well before we get this close to the drilling; a series of carriages containing staff amenities, first aid room, control room and transformers precede the TBM, and friendly faces appear from small doorways to say “hello”.

The magnitude of the TBM becomes apparent while standing right next to it. The platform I’m standing on, which is attached to the side of the machine, shakes incessantly as it cuts into the rock, spitting out spoil onto a continuous conveyor belt that runs the length of the tunnel.

The TBM’s best single week was in November 2008, when it excavated 220.62 m, while the best single shift was in May 2008, excavating 30 m. Today we won’t see the final breakthrough moment, but it’s clear that the anticipation is mounting, and for the workers on the TBM, it will bring a sense of achievement.

“The TBM operates 24 hours a day, seven days a week, and we have 11 shifts a week. Saturday and Sunday we have maintenance in,” says Paul.

Although hard work, it’s easy to see that there is a sense of pride for the project. This is highlighted when on our return to the MacDow site office, when Paul pulls over to ask a colleague about getting a picture of the TBM framed.

“Yeah, I’ve got one hanging up in my living room,” our friend replies.

“There’s a local bloke at the Post Office that frames them and puts plaques on them. And I think the colleague got the pictures done in Albury, where they had them blown up” says Paul

Asked about MacDow’s plans for future hydro projects, Paul says there are potential projects nearby in Victoria and elsewhere in Australia. MacDow is currently working on a hydro project in the Philippines and is strongly focused on the Asia-Pacific, Sub-continent and Middle East for future opportunities. Paul himself is heading to Singapore to work with MacDow and the Singapore Government’s Land Transport Authority on an underground station and tunnelling project.