Crafers Highway - Eagle on the Hill tunnels

摘要

The Eagle on the Hill tunnels form part of an upgrade of Mt Barker Road, which winds steeply through mountainous terrain, 15 km to the southeast of Adelaide in South Australia. Twin tunnels, spanning 15 metres and running in parallel for a length of 480 metres, are excavated in slightly weathered high strength slates and very high strength qartzites. Steeply dipping slate cleavages and the high fracture ratio have resulted in slope stability problems in the project area. A winning feature of the alternative tender was the use of canopy tubes, flexible steel ribs and shotcrete to replace up to 40 metres deep portal cuts in unstable rock with driven tunnels. The support concept allowed the safe driving of the tunnel portals with as little as 2 metres of overburden. Monitoring of the support performance by the Sydney based design team was achieved through electronic transfer of photographic and survey information, telephone and fax communications and regular site visits.