Costain has won an award for innovation for its novel use of a new scanning instrument in the London Tunnels.

The company won the ‘Most Innovative Use of New Survey Technology’ award, presented at the London Survey Dinner, for its use of the Leica MS50 scanning total station to control the spray concrete lining transitions at adits which form part of the London Power Tunnels contract under which Costain is driving 33km of tunnels under the capital.

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.

The crews manning the excavator driving the adits had to cut them to within 1cm of their final profile – and initially, found difficulty in achieving the required tolerances. Nigel Drayton, Senior Survey Manager at London Power Tunnels and his team then 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 set up the MS50, which nods as it rotates, in under five minutes. The scanner records at 8,000 points a second, determining whether the cut is accurate or whether re-excavation is necessary. The data was taken whilst the MS50 was still in the tunnel,  imported onto a laptop, and then through Amberg TMS software to create profiles, or ‘slices’, through the excavation. Within 10 minutes it was possible to say whether the tunnel was OK or not.

Once a satisfactory tunnel profile was achieved, it was given a spray concrete lining. The MS50 was then used again, while the spray concrete was still workable, to check that the new, lined, tunnel was to the correct profile. This then allows the thickness of the sprayed concrete to be analysed –which Nigel Drayton explained was critical for the structural integrity of the tunnel, providing  an excellent Quality Assurance tool, commenting:

 “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.”