RAIL SURVEYING
Shining a light
Network Rail operates a fl eet of measurement trains used to monitor Britain’s railway infrastructure. Rail Technology Magazine spoke toBrendan Rice to fi nd out more
M
Surveying the longest tunnel in the world
O
ccupying the primary north-south transit
corridor in Switzerland, the New Rail Link through the Alps (NRLA) is a key component in Europe’s growing network of high-speed railways. When completed in 2017, the NRLA and its high-speed AlpTransit trains will cut the travel time between Zurich and Milan by more than 25 percent. The centrepiece of the new system is the Gotthard Base Tunnel. At 57km (35 miles) long, it’s the longest tunnel in the world.
The Swiss surveying company terra vermessungen ag is providing a variety of surveying services in the northern sections of the Gotthard tunnel. The diverse work, demanding requirements for precision, and diffi cult working environment present unique challenges for the surveyors and their equipment.
One of the biggest hurdles comes from the narrow sight lines in the tunnels. When sighting in a tunnel, it is common to have multiple prisms visible in a total station’s fi eld of view. Manual observers can distinguish the desired target from the others but this approach is too slow for the project’s needs.
To solve the problem, terra vermessungen selected the Trimble S8 Total Station. The 1” robotic instrument combines precise measurement with Trimble FineLock™ target technology to provide automatic pointing and fast, high-accuracy measurements in the confi ned spaces.
As Gotthard construction progresses, terra vermessungen will continue to keep their Trimble systems busy. For the TBMs alone, terra vermessungen will set out approximately 7,000 points. Urs Müller, survey engineer for terra vermessungen, is pleased the new technology has repeatedly proven its value. “After a few hours, the sceptical attitude of the heading foremen changes,” he explained. “And after a few days, they do not want to continue without it.”
60 | rail technology magazine Dec/Jan 11
onitoring Britain’s railway infrastructure, sprawling out over thousands of miles of track across the country, is an important and challenging task.
In order to gather the most accurate information possible, Network Rail has a fl eet of measurement trains which use the very latest in surveying technology to keep tabs on Britain’s railway assets.
“All of our measurement trains use laser technology in one form or another and it is the most relied-upon measurement type we take,” says Brendan Rice, examination resource manager at Network Rail.
“Up until the late eighties and early nineties we were still using some mechanical measuring systems on the trains, which we then began to supplement with laser systems and the two worked hand-in-hand for a number of years.
“We have now begun to rely solely on laser-based measuring systems for some of the new types of measurements we are taking. These now form the backbone of every measurement we take, including overhead line, structure gauging and track geometry.
“These are all now laser-based measurements and are all taken in the same way, using point- to-point measurement. In other measurements we will use a fan of lasers, such as picking the gauge profi le of platform or tunnels and this is carried out by our structure gauging train.
“Before we used lasers, we used to use a white light system, which was where high intensity bulbs illuminate a very thin strip inside the tunnel and then cameras zoom in on the illuminated gauge profi le which is produced. Then through a series of complex calculations and a bit of trigonometry surveyors were able to work out the gauge measurement of either the tunnel or platform being measured.
“However the problem with using this kind of technique was you had to operate the system
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