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Raising the bore in Switzerland

Work on a new pumped storage power station in Switzerland has now reached the shaft construction stage and main contractor Marti worked with tunnel boring machine (TBM) specialist Herrenknecht to find a solution.

The tunnels for the new 900MW Nant de Drance power plant in Valais have already been built but the vertical shafts need to be completed if the facility is to come on stream in 2017 as planned.

Gripper TBMs supplied by Herrenknecht were used to drive the tunnels and Marti worked with the company to develop a raise boring rig (RBR) and a shaft drilling jumbo to drill the two 424m deep vertical shafts that will connect the upper Vieux Émosson reservoir with the machine cavern.

The work started with the boring of a 381mm diameter pilot hole from the top down through the 150MPa strength rock and up to 62m progress per day was achieved at one point and the RBR will be used to ream the 2.44m diameter bore.

The shaft drilling jumbo is now being used to enlarge the shafts to 8m diameter using two drilling and blasting rounds of 2.5m, each with 120 blast holes per day.

Work is progressing well and Marti is confident of achieving its 2017 finish date.

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