The Foundations of the Rhine Bridge Fussach-Hard (Austria)

Due to the high damage potential that a possible flood event has for the densely populated areas along the 26 km-long “International Stream” of the alpine Rhine, the discharge capacity needs to be expanded from the current 3100 m³/s (100-year flood) to 4300 m3/s (300-year flood), in line with the requirements of the Swiss-Austrian project RHESI – Flood Control for the Rhine Valley. In this context, the existing 255m-long Rhine Bridge connecting the Austrian towns of Fussach and Hard is no longer able to ensure the primary framework conditions for flood protection and needed to be replaced by a new structure. The new Rhine Bridge Fussach-Hard, a state-of-the-art steel composite bridge with a separated rope construction, was designed to meet the new requirements for flood protection as well as to satisfy the increasing volume of traffic. The extremely unfavorable subsoil conditions, consisting of shallow, very soft to soft plastic lacustrine clay deposits, required a deep foundation solution for the substructure (abutments and piers). Due to the high flood risk, the construction of the substructure could only be carried out during a period of low water discharge (winter), resulting in a very tight construction schedule (winter half-year 2020/2021). For the deep foundation of the substructure, several options were evaluated. Finally, a solution consisting of pile grillages, executed with ductile cast-iron driven piles (320 mm of diameter), was adopted for the project. The fast, safe and simple execution of the piles allowed for the successful erection of the substructure within the limited available time frame. The completion of this construction stage was critical for the further phases. After a construction time of only 28 months, the Rhine Bridge Fussach-Hard was officially opened for traffic on November 18, 2022. The following technical paper presents an overview of the adopted deep foundation solution, focusing mainly on the design and execution of the piled foundation. Furthermore, additional topics such as the sustainability of the adopted solution and possible optimization measures will be discussed.