The northern Spanish city of Bilbao upgraded its sewage system. Retention basins, pump stations, treatment plants and over 265 kilometers of sewage pipe with a diameter of up to three meters were built in various districts of the city. One of the most challenging sections was the suburb of Basauri where the 2.5-kilometer-long sewage tunnel being installed ran through limestone with a hardness level of 60 to 90 Megapascal.
The technology used was especially conceived for the given geology, in particular the cutterhead of the extended AVN1600TE. An integrated crusher broke up the excavated limestone for removal. Thanks to an automated bentonite lubrication system, it was possible to reduce the number of intermediate jacking stations to the minimum. The machine achieved a tunnelling performance of up to 42.5 meters per day, so that the project was completed one month earlier than planned.