Design and construction of cross passages at the Storebaelt Eastern Railway Tunnel

Twin 8km long, 7.7m internal diameter (ID) tunnels carry the railway between Zealand and the island of Sprogo. These tunnels were driven through glacial tills and the underlying Upper Palaeocene Marl by earth pressure balance TBMs and generally lined with segmental rings of precast reinforced concrete. Twenty nine 4.5m ID cross passages were bored and lined between the twin tunnels to act as equipment rooms and as escape passages. The paper describes the geotechnical conditions anticipated and encountered, and the development of the design from the tender stage onwards. It was realised that the ground conditions might be difficult so provision was made for geotechnical investigations and ground treatment through the main tunnel linings at each passage location. The construction method and design details were strongly influenced by the need to ensure safety during construction, and a range of measures were made available and adopted as necessary, including ground treatment and freezing, local and overall dewatering, use of a pilot tunnel in the tills, piecemeal excavation and primary support of the large collars at the junctions with the main tunnels, safety doors and temporary props in the main tunnels. Details are given upon the rates of progress achieved in the successful and safe construction of the cross passages.