Artifical Barrier to Deviate Ground Water Aggressive to Concrete.
As one of the most important east-west connections, the A4 connects the centres of the Rhine-Main and Ruhr areas with Thuringia, Saxony and the eastern and south-eastern European economic area. As part of the project “Extension or new construction of the BAB 4”, the twin-tube tunnel Jagdberg, with the standard cross-section RQ 33t and a length of approx. 3.1 km, is to be constructed between the Magdala and Jena-Göschwitz junctions. It was excavated using mining methods and has seven cross passages, three crossings, five breakdown bays in each tunnel tube, a smoke extraction shaft (approx. 140 m high in the middle of the tunnel), an operating building in the area of the west and east portals and a ventilation building above the tunnel.
Extensive investigations of the subsoil situation were already carried out during the design planning and preparation of the tender for the construction project. These findings were later, during the construction of the tunnel structure, largely confirmed. Driving and securing of the tunnel was ahead of schedule. The fault zone, which runs approximately in the middle of the tunnel and represents the geological interface between the Muschelkalk and Bundsandstein (Röt), was traversed more easily than expected. As the rock was compact and undisturbed, the subsoil investigations did not indicate that the Röt was a waterway. During the driving work and the service life of the tunnel outer shell, the areas with open bottom without mountain water ingress had been encountered and developed. The amounts of mountain water predicted in advance by the subsoil expertise were not encountered to the extent expected.
However, in order to prevent water from the overburden (Muschelkalk) from entering the reddish area, a bulkhead or a barrier and the targeted collection of possible seeping mountain water were initiated. Further investigations had come to the evaluation that possible water ingresses are extremely aggressive to concrete (containing sulphate). Injection curtains with barriers were planned and implemented for the targeted capture and safe drainage of possible seeping mountain water.
A barrier created by injection (injection screen), subsequent controlled discharge of the mountain water into a drainage system installed subsequently.