Sprayed concrete for the new Cologne-Rhine/Main express railway line

Construction work for the new 219-km-long Cologne-Rhine/Main high-speed railway line for passenger transport is in full swing. Apart from numerous structures such as slope stabilisation measures, retaining walls and 18 viaducts with a total length of approx. 6 km, 30 tunnels - some 47 km long - have to be constructed 24 of them are driven by underground means. While one tunnel at the junction of the branch line to Wiesbaden consists of two single tubes advanced by shield tunnelling, all the other tunnels are double-track structures realised by means of the sprayed concrete method. Many of the tunnels are located in water conservation areas, and therefore ii must be ensured by ail means that the groundwater table will rise again and the alkali content of shotcrete be limited. The standard sprayed concrete methods ore applied such as cry-mix shotcrete in combination with oven-dry or earth-damp aggregate, and wet-mix shotcrete with low-alkali or alkali-free accelerators. Tunnel driving in the generally strongly weathered rock with low overburden and many undercrossings of the Cologne-Frankfurt motorway as well as other traffic routes and structures constitutes a particular challenge of this project.