WOLFF luffing cranes in operation at a hydroelectric
project in the Swiss Alps

The Valais Alps is home to one of the most powerful pumped storage power plants in Europe. The current underground facility uses the downward slope between the existing reservoirs of Vieux Emosson (2,205 m above sea level) and Emosson (1,930 m above sea level) to generate energy. One of the objectives of the project is to double the storage volume of the higher reservoir, Vieux Emosson, which means that the height of the dam has to be increased. The responsible contracting companies, Groupement Marti Implenia (GMI), commissioned premium manufacturer WOLFFKRAN with this job, who had already been involved in the construction of the original dam wall of the Vieux Emosson in the 50s. The new challenges on the high alpine construction site are now being tackled by the luffing cranes Big WOLFF 1250 B and WOLFF 500 B.

Work already began in 2008 with the expansion of the access tunnels and the development of the construction sites. The WOLFF 1250 B came into operation in the spring of 2012 for the demolition work on the crest of the wall. The WOLFF 500 B was put to use last year with the start of the concreting work to extend the height of the wall. By fall of 2014, the wall will be increased by 21.5 m to a final height of 65 m. As a result the storage volume of the Vieux Emosson will be doubled to 25 million m3.

High load capacities required for the demolition work
On the one hand, the contractor decided to work with WOLFF
luffing cranes because of their high load capacities. The 1250 B,
one of the strongest tower cranes in the world, is in operation with
an 80 m jib and a maximum load capacity of 40 tons at the Vieux
Emosson reservoir. The high load capacity was required to lift the
heavy eroding machines and excavators onto the wall. The
excavated material could also be lifted from the wall in 40-ton skips, saving a lot of time and money. The WOLFF 500 B, with a 60 m jib and a maximum load capacity of 30 tons, supported the Big WOLFF in the concreting work to raise the height of the wall. In total, the red giants broke down 25,000 m3 of concrete and will move 70,000 m3 of concrete to extend the height of the wall.

Impressive assembly concept
But the two WOLFFs were not just ideally suited because of their load capacity on this hard to reach construction site in the mountains.

WOLFFKRAN stands head and shoulders above the competition with its sophisticated assembly concept," says Christian Maillet, site manager at GMI. "Due to their long jibs, the tower heights of the luffing cranes, at 30 and 45 m, could be selected significantly lower than would have been possible with a saddle jib crane. This meant that both WOLFFs could be erected to end height with a mobile crane and did not have to be climbed afterwards," explains Maillet. "Assembling tower cranes at this level represents a major challenge," says Philippe Gremaud, area manager at WOLFFKRAN. "Heavy snowfall and severe cold weather added further complications to the assembly. But we were able to draw on our experience with such complex assembly conditions, and managed to erect the 1250 B in seven days and the 500 B in just three."

Ideal when space is limited
The luffing cranes are also the right choice for the cramped conditions at the site, because they are designed to work as space-efficiently as possible. The dam is flanked at both ends by high rock faces. Using the WOLFF luffing cranes, it is not necessary to slew over the high rock faces since they can slew past them very closely. Furthermore, they can rotate freely at any time on the narrow mountain construction site with their jibs in a steep position.

The WOLFFs are in hibernation, so to speak, since November 2013, because work cannot proceed at these altitudes due to the large amount of snow and high wind speeds. To avoid any danger, the jibs of the two cranes were dismantled and stored safely. The red giants will be able to resume their work in the spring. To complete the dam, they will be on higher towers of 50 and 60 m respectively.

New energy for Switzerland
The pumped storage power plant is expected to go into operation in 2018 and generate up to 2.5 billion kWh of electricity a year. With a total capacity of 900 MW, it is designed to cover the increased energy demands of the Swiss electricity network and the Swiss Federal Railways SBB.

Source: WOLFFKRAN International AG


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