TBM powers Swiss drive for renewable energy Aug 2012
Herrenknecht News Release
The completion of two TBM-excavated utility tunnels is enabling the Swiss city of Bern to move towards full commissioning of a new energy centre that will help it reach an eventual goal of supplying its population and businesses with electricity from entirely renewable sources by 2039.
Advance of the 3.6m diameter AVN pipejack

Advance of the 3.6m diameter AVN pipejack

In June 2012 Bernese energy supply company Energie Wasser Bern (EWB) began the gradual commissioning of the new Forsthaus Energy Centre. The combination power station, unique in Switzerland, combines rubbish recycling, wood-burning and gas turbines to process steam for industry, district-wide heating for Bern residents, and electricity.
A 3.6m microtunnelling TBM from Herrenknecht was selected by contractor Implenia Bau AG to excavate two utility tunnels to the nearest district heating hub, for a total length of more than 500m (Table 1).
These run at a depth of between 7m and 18m through gravel and clay subsoils to connect the Forsthaus Energy Centre to the district heating network.
Ground movement control was a critical element of the first 485m long section of the drive, with the alignment taking the TBM beneath railway tracks at the nearby freight depot. The underground team steered the AVND machine precisely so that normal rail operations could continue throughout the excavation.
Microtunnelling machines of the type used in Bern are successfully used worldwide in the construction of water supply and sewer tunnels and are ideal for tunnelling below the groundwater through wide range of soil geologies. Pipe segments to secure the tunnel were pushed forward from the launch shaft using the pipe jacking method.
First breakthrough after nine weeks

First breakthrough after nine weeks

Breakthrough on the first drive took place at the Bernese construction site just nine weeks after launch. In the intermediate shaft the excavation team turned the Herrenknecht TBM through 90° in the direction of the next section. For the second excavation the supply logistics for the machine, including the delivery and removal cycle of flushing liquid, had to be adapted in such a way that the above-ground equipment could remain in the original launch shaft.
Other hazards along the final 80m long alignment included a 300-year-old oak tree that had to be passed under without damage to its roots. Following successful completion of the tunnelling work the lines for district heating, steam and electricity were installed.
In early 2013 the new Forsthaus Energy Centre will be connected to the district heating network and normal operations will begin. The former 60-year-old waste incineration facility will be demolished and the new power station will produce about 290,000 MWh of district heating, 40,000 MWh of steam and 360,000 MWh of electricity per year - approximately a third of the city's electricity requirements.
Table 1. Forsthaus Energy Centre utility tunnels, Bern, Switzerland
Machine data - Project data -
Machine type AVND2500AH Site owner Energie Wasser Bern
Diameter 3.6m Contractor Implenia Bau AG
Cutterhead power 400 KW Drive lengths 485m + 80m
Max. torque 1,600 kNm Inner diameter 2m
Weight 130 tonne Geology Gravel, clay

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