Installation of rock support is substantial, absorbing some 15.6% of working time to date. The tunnel as designed is largely unlined, having systematic rockbolting for long-term stability, shotcrete where required and in-situ concrete lining in the worst sections. T1, the lightest category of support (eight rock dowels on 1.8m spacing across the crown) was expected to support most of the tunnel, or 4375m of the 9616m TBM drive. T1A and T2 (rock dowels, shotcrete, wire mesh and steel straps) would support an additional 4335m. T3, the heaviest support, was expected to be required over 906m, and only over 345m in the first 4215m.
In December 1999, with the face at 3650m into the drive, some 374m of T3 support had been installed. T1 support had to be divided into T1l and T1M to meet conditions over 1818m and 805m respectively. There had been little T1A support at 37m and T2 covered some 564m. There had also been rock falls from the crown and the walls of the tunnel.
Related Files
Support Elements
