On August 12, 2017, construction work at the German Rastatt Tunnel came to a halt due to a displacement of concrete segments in the east bore underneath the Rheintalbahn (Rhine valley line) at Niederbühl. resulting in a settlement of the railway tracks. The immediate closure of the Rheintalbahn lasted until October 2; the tunnel’s damaged area was backfilled with concrete over a distance of 160 m and the Rheintalbahn tracks had to be relaid on a concrete slab measuring 275 m in length. The evidence gathering and arbitration process to clarify the technical reasons for the incident is expected to be finished by mid-2020.
Edgar Schömig, board member of the Ed. Züblin AG commented the continuation of construction works: “We have developed a technical concept for completing the structural work for both tunnel bores. We will finish the west bore by means of mechanised excavation and continue on the east bore with cut-and-cover.” Dr. Dirk Rompf, board member for Network Planning and Large-scale Projects, DB Netz AG, said: “With this concept the tunnel will probably be operational by the end of 2025.”
After the incident in the east bore, the western TBM had continued excavation until it reached the Rheintalbahn area in early December 2017 after 3672 m of tunnelling. In April 2019 it was moved into a maintenance shaft to be prepared for the remaining 200 m drive. The TBM uses bentonite slurry for EPB excavation. To prevent the slurry from emerging under pressure at the surface, gravelly sand is being poured next to the tracks still resting on the concrete slab. The structural work for the west bore is expected to be completed in late 2020.
The east bore underneath the Rheintalbahn tracks, which had to be backfilled with concrete, has been opened again in the area of the concrete plug. DB German Railways cannot continue work there until structural works at the west bore have been finished, because the Rheintalbahn tracks will have to be relocated above the west bore over a distance of 700 m. Then a construction pit 200 m long and 16 m wide is excavated (see Fig. 1), the existing tunnel section and the TBM are dismantled and the section is being built by cut-and-cover. Finally, the construction pit is backfilled and the original alignment of the railway tracks is restored. The works are scheduled to start in 2021.