AUSTRIA'S SECOND longest tunnel is to have another tube driven alongside to cope with increased traffic.
At 10km, the Plabutsch Tunnel is the longest on the 230km Pyhrn A9 motorway. When it opened in 1987 it was designed to handle 20,000 vehicles a day, but traffic volume has doubled in the last 10 years.
Tunnelling began on the second tube in July 1999. The tunnel is being excavated using drill and blast techniques. It has a cross section of 100m 2and an 8m wide floor. Geology on the route comprises sedimentary sequences of the Graz Palaeozoic and Tertiary dolomite of the Graz basin.
Quartz and dolomite sandstone is also present.
In January 2001, work began on a 3. 8m wide, 0. 8-1. 4m deep trench for service ducts. This is being tackled by a 48t Wirtgen Surface Miner fitted with Betek point attack cutting tools with soldered tungsten carbide tips, operated by Austrian company Bernegger Bau.
The Surface Miner uses an integrated levelling system to cut the trench precisely according to the profile. A depth of 300mm is being achieved in one pass by the machine and, depending on the hardness of the rock, between 100m 2and 300m 2of material is excavated an hour.