CONSTRUCTION OF THE SECOND BORE OF THE PFAENDER TUNNEL

摘要

The Pfaender Tunnel bypasses the residential area of the city of Bregenz at thernnorthern end of the A14 Rheintal Motorway. The alignment of its second bore runs underrnthe Pfaender massif for more than 6.5 km. The route runs through geology describedrnas the standing midland molasse, a sequence of beds from the Neogenic period (LaternTertiary), today mostly consisting of conglomerate, sandstones, marl-sandstones,rnmarl and clay-marl. The second tube was excavated with a single-shield tunnel boringrnmachine working from the starter tunnel in the North to an existing short bore inrnthe South. The tunnel’s standard cross-section is a circular (bored diameter 11.92 m)rnand the external diameter of the segmentally concreted lining is 11.62 m. This paperrndeals with the main issues related to the issues of an alternative TBM tunneling tenderrntaking into account the swelling tendency of the marl, and also deals with the constructionrnof Austria’s first road tunnel to be driven with a TBM. The problems encounteredrnwhen driving a TBM in divided cross-sections (bench and invert sections without toprnheading) in soft ground and the solutions adopted on site are discussed. This paperrnalso deals with the complex construction of voluminous enlargements (traffic lay-bys,rnservice niches, ventilation caverns), where the circular segmentally lined TBM tunnelrnhad to be widened up and relined using the SEM/NATM shotcrete tunneling method.