Something quite remarkable happened in Southampton Tunnel this Christmas, a rare event in the world of railway engineering: absolutely nothing. That is because over the previous festive period, the team delivering a challenging project to accommodate high-cube containers exploited best practice and technology to deliver in just one Christmas a scheme originally planned to run over two.
It was an approach that clearly impressed Iain Coucher, Network Rail’s former Chief Executive. At the time, he wrote in his blog that “Over the [2009-10] Christmas period, all of the directors went out to see some of the work being undertaken on the railway – investment and maintenance alike. I had the opportunity to see the team working in Southampton Tunnel – a vital project which forms part of the programme to allow bigger freight containers to move from the docks in Southampton to north-west England. The tunnel has been there for many decades and indeed has been subject to several attempts to widen it in the past. It is a tight tunnel with a difficult curve towards the north.”
“The project is a wonderful example of high-tech precision in a world of heavy engineering… using slab-track techniques, in which we set the track to less than 1mm accuracy, we can get freight trains through the tunnel, at speed, with around 50mm (that’s 2” in old money) clearance. We had a closure of ten days…and once you’ve started, you can’t go back! So, well done to everybody that worked on this… I know that this didn’t just happen…it was two years in the planning. And that’s it – we shouldn’t have to go back again for years!”
The surveying key
The work was part of a £71 million project designed to remove up to 50,000 lorries a year from the roads of southern England as well as providing a cheaper, quicker and more practical way of transporting goods around the country. At Southampton, the work involved Network Rail lowering both tracks through the tunnel. Working over weekends and midweek nights during December 2009, as well as the Christmas blockade, disruption for passengers was significantly reduced, with the work finishing more than a year ahead of schedule. At the time, Richard O’Brien, Network Rail’s route director for Wessex, said “the innovation and commitment of our engineers means we were able to keep disruption to a minimum. In the past, a job like this would probably have meant the railway being closed for 12 weeks.”
The decision to harness the best measurement technology on offer was key to this success. It involved use of the Amberg GRP3000 which permits many functions to be performed simultaneously by the same surveyor. This led to an increase in achievable accuracy on site.
The system delivers sub-mm cant and gauge and 1mm in plan and profile position using the GRP’s secure and stable attachment to the rails, plus 3mm clearance accuracy with the integrated GRP profiler. In terms of production, it allows comprehensive reporting to the design alignment in real time to both rails simultaneously, instantaneous clearance calculation with plotting to the vehicle profile and, crucially, removal of the inevitable small differences in position from one total station set-up to the next. This preserves the 1mm accuracy of the track positioning throughout.
Without the GRP3000 it would have been necessary to deploy and coordinate both setting out and clearance teams, together with not inconsiderable calculations from a surveying expert on site to resolve the reported differences in position from one total station set-up to another.
Well-deserved gong
It is evident that with all track position surveying, setting out and gauging is paramount. With slab-track the most extreme pressure on these elements is experience. The work must be right, first time, every time – otherwise all the assembly, welding and concreting has been for nothing. The selection of the GRP3000 and the investment to properly exploit its capabilities was amply repaid with nil surveying, setting out and gauging errors through Southampton Tunnel.
The work went on to be awarded Network Rail’s Project of the Year whilst the GRP methodology has been adopted as the company’s standard for slab-track. And so, remarkably, Southampton Tunnel experienced a very quiet Christmas 2010.
