Design and construction of the new railway bridge over the River Neckar – Challenges of the foundations

Abstract

AbstractAs part of the Stuttgart 21 infrastructure project, German Railways is building a four‐line railway bridge across the River Neckar in Stuttgart, work started in 2016.The Neckar railway bridge has an overall length of 345 m and has two abutments and six support axes. The structure crosses rail lines from the urban transit (Stadtbahn), the main trunk road B 10, inner city roads, the Neckar River, pedestrian and cycle ways as well as diverse public and private utilities.The bridge structure is located within the core mineral water protection zone, with its strict restrictions regarding the permissible depth of penetration into the subsoil and groundwater reservoirs. The mineral water springs lie within the construction site 26 m below the surface as artesian aquifers with an artesian pressure of ca. 10 m above ground level. From a groundwater management perspective, and following a program of five ground investigations and their evaluation, a raft foundation at the mid‐level of the lower Keuper, built using cut‐and‐cover technique with a compressed air caisson, was chosen as the most economical foundation type for the three primary supports.A further programme of hydrochemical and geomechanical ground investigations was undertaken during the construction design phase. Following an evaluation of these additional ground parameters, it was possible to replace the compressed air caisson with a more economical deep foundation using large diameter piles. A management concept for possible scenarios was needed for the large diameter pile construction to achieve the required consent for exceptions from the ban on ground penetration in the area of the mineral springs.