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Across the Outback on a shoestring

Railways Australia

Work is now under way on one of the biggest infrastructure projects ever undertaken in Australia - the £470M, 1,420km Darwin to Alice Springs railway. Steve Turner went to find out more.

The idea of a railway to connect the Australian states of Northern Territory and Southern Australia was first mooted back in 1911. But for one reason or another the link - to reduce the time it takes southern freight to reach the northern port of Darwin where it continues on by ship to vital Asian markets - has always been shelved. Until now.

After many years of negotiating and route planning the Asia Pacific Transport (APT) consortium is on site and making steady progress through some of the world's most inhospitable terrain.

The first rails were laid last April, and when the line is completed in 2004, combined with a massive redevelopment of the port of Darwin, it will provide massive opportunities for Australia's importers and exporters.

The route consists of a single line track with passing loops, and runs the 1,420km from Darwin in the North to Alice Springs in the centre of the country. At Alice Springs it will connect to the existing line that links to Adelaide in the south, and the southern states rail network, creating a land bridge to Asia.

Total project cost is £470M.

Construction is being undertaken for APT by ADrail, a consortium responsible for design and construction of the line.

ADrail is headed by Halliburton KBR, along with Barclay Mowlem, Macmahon and John Holland.

Cost targets are stringent, and because of this the team is not trying to find the latest and greatest ways of doing things, but is finding clever ways of doing ordinary things more cheaply.

The railway is being designed as it is built, and although nearly 30% of the civils is now complete and track laying has started, designing continues and will do so for the next six months.

Everything is overlapping, but the team is managing to stay ahead so no one is being delayed.

The major works being undertaken over the last nine months has been shaping the formation.

The line sits on an embankment approximately 1m high and 6m wide, constructed from natural soil found along the route. As project design manager Charles Duncan explains, 'We are being selective, but basically we are stuck with what is there.'

Material is excavated using large scrapers, then formed, watered and compacted. Culverts are added to allow water to pass through.

Two construction depots are being used as bases for the job, through which will pass the estimated 2M sleepers, 8M clips, 2.6M tonnes of ballast and 2,800km of rail required.

The depots, one based in the north at Katherine, the other in the south at Tennant Creek, are the hubs of the job and starting points for the work. They house two massive sleeper factories which have been operational since November 2001, each capable of producing 2,400 sleepers a day.

Rail is also delivered on lorries to the depots in 27.5m lengths where it is welded into 357.5m lengths and taken to site by train.

Construction track laying trains - one of which was already in use in Australia, the other built specially - are based at each depot and work on a 24 hour cycle. Six days a week the trains are loaded up with sleepers, rails and ballast. They move towards each other from the two depots and lay track on the formation before returning to be reloaded for the next day.

Each train is programmed to lay 2.1km of track a day, six days a week, and it is hoped to complete the 700km between the two depots by the end of the year. Work will then start going north from Katherine and south from Tennant Creek at the same rate. Only when the trains are travelling more than 360km from the depots will the 24 hour cycle not be achievable.

Every 100km between the two main depots are camps to house staff.

That such rapid progress has been made in such difficult conditions is testament to the staff working in these camps. The heavily vegetated terrain is very flat and ill defined and it has proved difficult to locate where watercourses will appear in the wet season.

The area is very flood prone, meaning that all 1,500 stream crossings need culverts. The required 100km of corrugated steel culvert pipe is being manufactured on site to reduce transport problems.

'Hydrology and culvert design have been the major challenges so far. There are few records available, and estimating appropriate flood flows for designing the waterways has proved challenging, ' says Duncan.

So far all the work has been in the dry season and the problem has been finding water in any quantity, vital for numerous construction processes. Drilling teams have operated ahead of the construction teams with hydrologists, prospecting to find suitable locations to drill for water. Ideally the team wanted to establish wells every 20km, but this has proved difficult.

As well as the streams, 92 more substantial waterway crossings need bridges, all with varying requirements. To reduce the amount of design work and cost, the consortium devised a system whereby it can design structures as it comes across the need for them.

'It is not quite Meccano, ' says Duncan, 'but it makes use of standard components so we configure it to suit sites.' The substructure uses driven tubular steel piles or steel tubes placed into bored holes standing on, or socketed into, rock and concreted in. The piles are joined by a fabricated steel headstock on top of which sit precast concrete beams.

Design time is saved as decisions can be made on site about the number and length of spans needed to cross the required waterways.

The exceptions to this system are five rivers with water permanently flowing in them, where somewhat bigger bridges have had to be designed.

The major bridges over the Katherine, Edith, Cullen and Adelaide rivers have some in situ concrete works in piles, pile caps and column stubs, explains British bridge engineer Mark Jordan, who is based in the Adelaide design office.

Fabricated steel columns and precast prestressed concrete girders support insitu reinforced concrete deck slabs.

The Katherine river has an 18m river surface level range between wet and dry season.

'There was much debate as to whether we should lift or launch the bridge deck across the gorge.

But the river reduces to a small flow during the dry season so lifting from the bed is possible' says Jordan.

The largest of the five bridges is over the Elizabeth river near Darwin. The 17 span, 500m long bridge crosses a tidal estuary subject to daily water variation of up to 8m.

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