Tunnel triumphs

24 April 2008

Due to open in 2015, the 9 m diameter twin-tube Gotthard rail tunnels under the Alps will be a marvel of modern engineering. With a total length of 57 km, this piece of infrastructure is designed to divert huge amounts of freight traffic from the region's roads, which should slash journey times as well as help reduce pollution in this breath- taking area.

As an excavation and drilling job, the Gotthard tunnel is larger than anything seen before. In order to be able to complete the work at least close to the scheduled time, the job has been divided in five parts. The longest, Bodio, is 16.6 km in length, while the shortest, Sedrun, is 6.8 km long. Sedrun contains the types of rocks that are the most difficult to excavate and drill. Located at the deepest point, it is in many ways the most interesting segment.

Although other sections are being excavated with tunnel boring machines (TBMs), Sedrun will be driven with drill & blast techniques due to the high degree of rock fracturing. The Agre Transco Sedrun Company is undertaking this work with 12 Sandvik Tamrock jumbos - six Axera T11 and four Axera T12 machines among them. In addition, 10 Toros are loading rock to be transported through the vertical access tunnel.

“Getting the work started was difficult. All the machines to be used at the beginning were lowered into the bottom of the tunnel piece by piece down the first vertical shaft. Completion of the second vertical shaft made it possible to transfer machines weighing up to 25 tonnes in one piece using the lift, which is 12 x 3.5 x 3 m in size”, said Jakob Lehner, who is working on the tunnel construction site.

“This project is unique and challenging. We are proud to be on schedule, even though we've experienced difficulties along the way. Particular attention has been focused on safety, and serious accidents have been avoided”, he added.

“The drilling is done using jumbo drilling machines. Each round comprises 120 to 140 holes. The explosives are transported to the site in a specialised vehicle, and the explosive emulsion is not mixed until it reaches the face. The detonation sequence begins at the centre and proceeds automatically to the edges. Approximately 450 tonnes of rock are removed at a time.

“The poisonous gases formed during the blasting are removed quickly and efficiently. Loading the blasted rock into the tunnel train in the narrow and poorly lit tunnel is a particularly dangerous work phase,” Mr Lehner concluded.

Concrete is sprayed on the blasted surface, and jumbos are used to make the 9-m anchoring holes as well. Agre Transco Sedrun will continue working at Sedrun in three shifts at least until 2008. •

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