In case you’re wondering this is all about how 10 Allison auto-equipped Astra HD8 trucks have helped make tunnel excavation duties more productive, reliable and easier at the Nant de Drance and Linth-Limmern power plants. As if you needed telling, the new underground hydro power plant is going to supply the future energy needs of Switzerland and its public transport system. And to help carry out the work the construction consortium GMI (Groupement Marti Implenia) responsible for constructing the tunnel and power plant caverns, and processing the excavated material, purchased six Astra HD8 (480 hp, 8×6, 48-tonne GVW) trucks with Allison 4700R model fully automatic transmissions. They’ve performed so well, a further order of four identical vehicles followed.

The Nant de Drance pumped-storage power plant, situated between two existing reservoirs in the Swiss/French border region between Martigny (Canton of Valais) and Chamonix will generate 600MW of electricity by utilising the water pressure resulting from around 300 meters of altitude differential. The plant is being built inside the mountain, at 1700 meters above sea level, with access via a 5.6 km tunnel. The construction consortium started work in January 2009 and will probably finish 2017. That’s the good news, the difficult bit is that the only access to the construction site, 2,000 metres above sea level, is via cable railway or helicopter. So all the machinery used for the tunnel operationsincluding all the excavators, heavy equipment and the Astra HD8 trucks has had to ‘fly’ up to the site via the cable system – complete with the panorama of the Swiss Alps in the background!

Being 2,000 meters above sea level in winter the access route is inevitably impassible–work normaly takes place between April to November, 24 hours a day, on three shifts. It goes with out saying that with strict deadlines to achieve the task it’s vital to have absolutely reliable vehicles that are productive and easy to drive. So naturally, the Astra’s robustness and heritage in the heavy-duty dump truck sector combined with Allison’s 4700R fully automatic transmission was the obvious choice for the job with the Allison auto specially designed to operate in the most difficult conditions, providing maximum driving comfort, uninterrupted power to the wheels and increased control of the vehicle at lower speeds. Each of the 10 Astra HD8s, were also ordered with an integral hydraulic retarder, partly due to the slope of 12 % leading to the access tunnels, which often needs to be mastered with a fully-laden vehicle.
The road to get to the landfill for the excavated material is very steep, and the allison autos retarder simplifies operations and provides extended brake life. The transmission’s torque converter, is also a key contributor to reducing maintenance costs. Torque multiplication delivers superior vehicle startability on steep gradients, precise control under heavy load conditions and constant vehicle acceleration for safe operation on any type of terrain. With no requirement for a dry disc clutch (as found in manual and automated manual gearboxes) associated maintenance tasks are eliminated. Another important consideration for the Swiss construction consortium was the change of drivers across the three daily shifts. As the company points out to BLB: “Our personnel working in tunnels are not used to driving all types of trucks, so it’s very important to us that vehicles are easy to manoeuvre. Only fully automatic transmissions can ensure an operation free of bad surprises, like clutch failures resulting from wrong maneuvers and subsequent downtimes for servicing. With Allison’s automatics, our operators were able to drive the Astra HD8 from the very first day. We are very satisfied with the trucks and by the premium service offered by Astra.