BRANISKO TUNNEL UNDER BUILD

This article discusses the design and construction of the Branisko Tunnel in Eastern Slovakia, which will use many different tunnelling methods to cope with its varying geology. The 5km-long tunnel is part of a motorway construction scheme, including about 40km of motorway tunnels as shown in a map, and due for completion by 2005. Its construction began in 1996 with the building of an exploratory pilot tunnel within the profile of the future northern tube, and was followed by works at both portals. In April 1997, driving of the south tube started from the west portal. The northern tube will be built in the next 15 to 20 years. Fortunately for the tunnellers, over 3.5km of the tunnel will be driven through Paleozoic crystalline rocks with only occasional faults; there are also claystones, sandstones and other sedimentary rocks. The pilot tunnel was drilled to enable detailed ground investigation, but it will also be used as an emergency escape route for the southern tube, with which it will be connected by links about every 700m. The south tube is being designed and built according to New Austrian Tunnelling Method (NATM) principles. Its cross section varies from 103 square m to 82 square m, according to rock type. Excavation began at both east and west portals, and is proceeding from both ends.