Eastlink's rail bridge slide

The heavy rail crossing for the Ringwood line on Melbourne’s Eastlink demanded great ingenuity and careful planning.   BY ADRIAN GREEMAN

Most of EastLink’s 88 bridges were kept as simple and straightforward as possible, precast for speed and economy and with logistics and sequencing the uppermost challenges for their erection. But the heavy rail crossing for the Ringwood line demanded much greater ingenuity and careful planning.

The bridge was always going to be a little unusual: heavy trains need stiffer, beefier crossings than other types of bridge, and even though the Ringwood line is mainly for passengers, not bulky freight, it is no exception. It also needed expanding from an existing two-line crossing to one with room for an extra rail in the future as demand grows.

Original thoughts were to remove the railway and its embankment and demolish a small existing bridge over an old road along the new highway alignment. In the space a new 105 metre long steel and concrete decked bridge could be built in situ, and then the wide cutting for EastLink could be excavated below, around the piers.

To achieve this, the railway tracks needed to be split apart onto new temporary track, supported either side around the bridge site. But there was simply no room to do that says Matthew Gault, the TJH project manager for the Ringwood north section of the project.

“There were industrial premises nearby which constrained the job and a railway station was also too close for train over-run safety.”

The diversion would also have meant running tracks on either side of the site, with the live train power lines sitting close to the work, which would be dangerous, particularly for crane jib movements and booms on other long-reach equipment.

There was space in the road reservation itself and it was decided to build the entire bridge 14 metres to one side of the existing track and then, when it was ready, slide it into place using powerful jacks. The railway would have to be shut for a short period but otherwise would keep running.  

Such methods have been used before but each is different and complex, demanding precise timing not just for the slide but also to prepare the track to receive the new bridge. Quite early on the engineers had to commit themselves to a programme because the rail operators, Connex, needed several months’ notice for an occupation of the tracks. A large fee is payable too.

Essentially the foundations and final columns of the bridge had to be installed first and then the crosshead supports for the bridge deck. Originally it was thought several possessions of the railway would be needed says Gault, doing one crosshead at a time but eventually the scheme was reduced to two.

The giant foundations for the four-span bridge, great 1.8 metre diameter bored concrete piles, could be installed outside the train ‘envelope’. Pairs of the piles at each of three pier positions, and for the abutments, were put in through the existing train embankment. These would go into the ground as support but would stand free in the top few metres once the ground was excavated around them, forming the columns of the bridge.

To do them, some speed restriction on the trains was needed, and safety watch, but otherwise the work did not interfere with the railway, says Gault.

The job was more difficult than usual, however, because the piles had to have their heavy steel reinforcement and connections done with unusual precision to allow the crossheads to slot in later. That had to be done five metres deep down into the piles.

“To use the drilling rig we had built the sloping embankment up to a level platform with spoil but this meant it was higher than the position of the final crosshead connection,” explains Gault.

Concrete was only poured up to the required level, leaving empty steel casing above. Workers then had to go down inside to break back the concrete, measure the positions accurately and install the stress bars.

While that was happening the big five heavily reinforced crossheads were cast a few metres away. Each 130 tonne unit was to be lifted into place and the site had to be prepared for the cranes and excavators needed for the operation over a weekend (booked for August 2006) so that it could all move in and out in a tightly controlled sequence to get things done in time. Over 200 men and dozens of machines, cranes, excavators and trucks were involved.

The big 500 tonne Demag crane, christened Snow White and used throughout the road project, was the main tool for lifting crossheads in. It was painstaking work to get them carefully between switched off overhead power lines and then rotate them 90 degrees to slot into place.

“First task in the possession was to rip up the entire train track, and then to dig trenches for the crossheads so they could be positioned on the piles,” explains Gault. All that had to be replaced and the tracks relaid by the Monday morning.

Unfortunately for the team, despite meticulous planning, there was a glitch. Part of the embankment had to be removed to allow the outriggers of the big crane to sit in close, and just at this point an old drain was discovered, with bad ground around it: taking this out and backfilling with firm material cost nearly 10 hours of the operation right at the beginning.

“Our geotech samples were done just two metres away and did not show anything,” says a rueful Gault. Some hours’ over-run on the possession, fortunately ameliorated by passenger buses which had been on contingency standby, cost the contractor a penalty. Despite that the operation went exceptionally well with the crossheads dropping into place exactly.

The event underlined the need for even more preparation on the second possession, already booked for a few months ahead just after the Christmas break. For this the bridge deck itself was being built in eight sections, tied together at the last minute. Everything was included from the steel beams and concrete deck up to walkways, ballast and track, all ready to go.

To move it, the bridge needed its own set of tracks. These were reinforced concrete beams which had a steel running plate on the top. Using Teflon bearing pads (the same as in non-stick frying pans) the bridge could be slid along, pulled by powerful hydraulic jacks, one 140 tonne unit at each pier and abutment.

The concrete beams were built to the ends of the new crossheads so that this rail could go on to them and carry the bridge into its final position. But the crossheads were now buried in the embankment and the work needed to prepare them for the slide was going to require another possession. Post-tensioning was needed, connections to the piles and installation of the slide rail.

Mulling over the problem, TJH had devised a clever way round the difficulty. Before covering over the crossheads with the reinstated embankment and track on the first occupation, a culvert was created over the top of each one made up with U-shaped precast concrete covers lifted into place. This left a space above the crossheads within the embankment which was large enough to work in, and importantly, safe enough.

Preparations concluded with a trial pull for the new deck a few weeks before the occupation, “which revealed some issues with the bearings,” says Gault.

On the day in January 2007, the second operation went exceptionally well. The possession started half an hour early and the teams of excavators and trucks worked at twice the estimated speed, removing the embankment and ground around the piers.

“In fact by midnight I was phoning the structural crews to come in immediately rather than wait until 6am,” says Gault.

A “float” of additional time had been left in the plans anyway, and despite the actual pull of the bridge going slightly slower than expected the work was completed well ahead of the possession end.

The bridge was in place with its track, the links to the main track either side were installed and tamped down and new power lines were installed to replace the old. Signalling was reconnected and trains were rolling through for the Monday morning rush hour.

• This article first appeared in World Highways and has been reproduced here with permission. Images courtesy of Heaven Photography.