The small hydropower plants on the Rio Vermelho will each feed 2–8.5MW into the public electricity grid in Brazil. Mechanically created tunnels conduct the water directly to the turbine house. A small dam is built in front of each tunnel portal to dam up water. The entire river water, however, must never be used to generate electricity, on an annual average no more than 55%.
For seven transfer tunnels with drive lengths between 280 and 3,000 meters, a maximum gradient of 7 percent and small curve radii of up to 300m, Herrenknecht supplied a project-specific designed hard rock Gripper TBM with a boring diameter of 2.85 meters. The compact machine design simplifies the transport to the jobsites in inhospitable terrain as well as assembly and disassembly. The 49 meter long TBM is equipped with five back-ups of up to 8 meters in length, which can be transported on standard trucks.
The target of one 2.2-kilometer drive with an incline of 4.3 percent is a steep slope. For the event that the machine could not be recovered in a target pit as planned, the TBM was designed for retraction through the tunnel. For muck removal, the site crew uses multi-service vehicles with muck containers from the Herrenknecht subsidiary Techni-Métal Systèmes. With a width of only one meter, the vehicles are particularly narrow and can also easily handle inclines and declines on the tunnelling routes. The TBM’s navivation system was supplied by VMT GmbH and a team of specialists from Global Tunnelling Experts support the local construction crew.