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Swiss setting for shaft drilling prototype 03 Sep 2013
Herrenknecht News Release
The last phase of excavation on the new 900MW Nant de Drance hydropower scheme in Switzerland is providing the testing ground of a new shaft drilling jumbo (SDJ) machine developed by Herrenknecht.
The SDJ reams pilot shafts to 8m diameter

The SDJ reams pilot shafts to 8m diameter

The SDJ is being used by contractors Marti Tunnelbau (RBR) and Östu-Stettin, Hoch-und Tiefbau to complete the three-phased excavation of the vertical penstocks for the pumped storage hydro scheme. As the third piece of Herrenknecht excavation technology used on the project, the SDJ follows on from a gripper TBM that completed the access tunnel to the plant, and a raise boring machine being used to raise the pilot shafts as the start of each penstock.
The two 424m deep x 8m i.d. penstocks connect the upper Vieux Émosson reservoir with the machine hall cavern, which lies beneath more than 600m of mountainous overburden in the Swiss Canton of Valais (Fig 1).
  • RBR raised the pilot borehole to 2.44m diameter

  • RBR method with pilot drill and subsequent raise

The new shaft drilling jumbo was commissioned in April this year to slash two smaller diameter raise bore pilot shafts to the full 8m finished diameter. Work by contractor Östu-Stettin, Hoch-und Tiefbau is progressing in two drill+blast rounds of 2.5m/day, each round comprising 120 charge holes.
Fig 1. Nant de Drance underground excavations

Fig 1. Nant de Drance underground excavations

Main project contractor Marti Tunnelbau start excavation of the deep penstocks with a 381mm diameter pilot borehole, and achieved a best daily performance on the first borehole of up to 62m through hard rock with strengths of up to 150MPa.
Marti and Östu-Stettin, Hoch-und Tiefbau then used the Herrenknecht raise bore to complete the preliminary expansion of the pilot shaft to 2.44m diameter. The 424m deep raise started in November 2012 and was completed in two weeks with the reamer reaching a top performance of up to 33m/day.
The pilot bore and preliminary raise boring of the second penstock, is scheduled to start this Autumn, with slashing to the final 8m diameter using the SDJ taking place later in the year.
Launch of the refurbished TBM on the access drive in 2011

Launch of the refurbished TBM on the access drive in 2011

Prior to shaft sinking work, Marti used the 9.45m Herrenknecht gripper TBM to complete the 5.6km main access tunnel to the plant, through a geology of gneiss, greywacke and granite. Located high in the Swiss Alps at 1,700m above sea level, the tunnel provides safe winter access to the plant during the construction phase and into its subsequent operation.
The refurbished TBM was used previously by Marti to excavate 10km of the Lötschberg baseline railway tunnel in Switzerland between 2000 and 2003. It was then used between 2005 and 2006 to excavate 3km of tunnelling for the San Pedro railway project in Spain.
Prior to the start of work on the Nant de Drance project, Herrenknecht refurbished the TBM's 5.09m main bearing at its Schwanau plant in Germany, and delivered new roof bolting systems and other spare parts for the large-scale project on the high mountain jobsite.
Construction of the Nant de Drance pumped-storage power plant marks a ground breaking turn in the energy policy of Switzerland, which is looking to reduce its share of electricity generated by nuclear power and replace it gradually with electricity generated from renewable energy sources. The Nant de Drance pumped-storage power plant will produce electricity from environmentally friendly hydropower from 2017 onwards, serving at the same time as a giant energy storage unit.
References
Extreme gradient challenges in Switzerland - TunnelTalk, April 2013
US debut for vertical shaft machine technology - TunnelTalk, April 2012

           

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