20 January 2014

Costain has won another award for innovation – this time for its novel use of a new scanning instrument.

The ‘Most Innovative Use of New Survey Technology’ award, presented at the London Survey Dinner in Mayfair, attracted a large group of senior surveyors from major projects, such as Crossrail and London Bridge Station.

The award was for Costain’s use of the Leica MS50 scanning total station to control the spray concrete lining transitions at the Milk Depot adits, part of the London Power Tunnels contract under which Costain is driving 33km of tunnels under the capital to help ensure its future electricity supplies.

The adits, or horizontal drives off vertical shafts, change from a circular to an elliptical cross-section. While the human eye can ascertain if a circular cross-section has imperfections in its shape, it is much harder to do so as the adits make the rapid transition to the elliptical format. And the crews manning the excavator driving the adits had to cut them to within 1cm of their final profile.

Initially, the crews found difficulty in achieving the required tolerances. Then Nigel Drayton, Senior Survey Manager at London Power Tunnels and his team, thought of using the new, £45,000 MS50 surveying instrument to achieve a solution.

Once a new section of tunnel had been cut, a surveyor quickly sets up the MS50, which nods as it rotates, recording 8,000 points a second  and determining whether the cut is accurate or whether re-excavation is necessary.

“I think the use to which we put the MS50 surprised everyone,” said Nigel. “Set-up and surveying was under five minutes and while still in the tunnel we would take the data, import it onto a laptop, run it through the Amberg TMS software and create profiles, or ‘slices’, through the excavation. Within 10 minutes we could say whether the tunnel was OK or not.

“The advantage of this is that it’s quite important commercially; you do the job once and it’s right. That’s a big saving.”

Once a satisfactory tunnel profile is achieved, it is given a spray concrete lining. The MS50 is then used again, while the spray concrete is still workable, to check that the new, lined, tunnel is to the correct profile.

This then allows the thickness of the sprayed concrete to be analysed: “That’s critical for the structural integrity of the tunnel. It’s an excellent Quality Assurance tool,” adds Nigel.

 

Ends