Use of the first multi-mode tunnel boring machine (TBM) in Eastern Europe has proved key to delivery of new tunnels on a rail upgrade scheme in the Czech Republic.
Main contractor Metrostav used the Herrenknecht in earth pressure balance (EPB) mode and then in single shield mode to drive the 4km long twin bore tunnels between Rokycany and Pilsen on the new high speed east west rail link.
Around two thirds of the tunnels were bored in EPB mode to drive the bore through
quartzite shale stone and clay soils but the single shield was needed for the final 1.1km to penetrate hard spilite rock.
Herrenknecht has said that each conversion as completed within the tunnel in less than two weeks. The cutting tools were also changed for the second section of each drive with larger diameter cutters used to create higher contact pressure in the solid hard rock and longer running times.
Completion of the tunnels reduces the average travel time between Rokycany and Pilsen by around 10 minutes and is a key part of the new high speed line that connects to Prague and the main European rail network.