GSR – Pretensioned Steel Arch: Reinforcement Technology Rethought

Abstract When an arch in tunnel construction needs to be reinforced, a temporary, self‐supporting support structure is required for the reinforcement. Until now, either support arches or lattice arches have been used for this purpose. The innovative GSR tension arch system has been available since 2018. The name GSR is derived from the German terms ‘gebetteter Spann‐Ring’ (embedded tension arch). This illustrates the system's range of applications. It can be used as a circumferential tension ring in the case of fully‐round arches, as a tension arch for vaults and as a stress‐free mounting system for basic arches. In contrast to the two aforementioned systems, the support structure is not located between the reinforcement layers, but is arranged on the mountain side. This opens up possibilities for designing the reinforced concrete inner shell that were previously not available, both technically and in terms of construction. In addition, the measurements taken throughout the entire installation process ensure a precise result for the concrete cover on the air side. Extensive laboratory and field tests have proved that the GSR tension arch system neither damages the tunnel seal nor impedes its movement during concreting. Since 2018, around 1,400 blocks have been built with the GSR tension arch in various projects. GSR tension arches have been installed in the Brenner Base Tunnel since summer 2024. A total of around 100 km of GSR tension arches will be used here over the next few years. The following section explains how the system works, its compatibility with the waterproofing, its design and its structural features.