Leica Geosystems has helped provide surveying services on the world’s longest rail tunnel.

The Gotthard Base Tunnel (GBT) is a 57 km railway tunnel beneath the Alps in Switzerland and took 14 years to build.

Leica’s surveying instruments are in use in all areas of the Gotthard Base Tunnel, according to the company.

As the client's surveyors, the consortium is responsible for ensuring the correct position, level and direction during the driving of the tunnel.

Ivo Schätti, a senior engineer for the surveying consortium Vermessungsingenieure Gotthard-Basistunnel said he used total stations, digital levels and optical plummets from Leica to ensure the tunnel was within the specified accuracy: 10 cm transversely and five cm vertically over the whole 57 km length.

 "Put simply, our duty was to see that the hole was built in the right place," he said.

The contractors' surveyors, the specialists in the companies directly involved in driving the tunnel, also used Leica total stations and levels, primarily for the control of the tunnel boring machine (TBM), setting out, profile measurement and levelling. 

Leica Geosystems instruments were also in use above ground to monitor the movements of the valley sides near the dam walls of three water reservoirs beneath which the tunnel passes.

"A tunnel always influences the water balance in the mountain. The loss in pressure due to the water extracted from the rock could result in the mountain literally collapsing," said Schätti.