CONSTRUCTION OF THE SECOND BORE OF THE PFAENDER TUNNEL

摘要

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