High-precision cut in the tunnel

As was to be expected, the tunnel surface was very irregular after completion of the blasting operations, and the floor needed to be lowered by 60 to 80 cm across the full tunnel width. A laser-controlled automatic levelling system installed in the surface miner 2100 SM enabled the surface to be lowered to the specified level with pin-point accuracy. The tunnel floor was produced quickly and with an extremely low tolerance of no more than +/- 1 cm.

Cutting of the limestone material took place in the miner’s fully enclosed cutting drum housing. The development of dust was greatly reduced by injecting water into the housing during the cutting operation. Loading the cut material on trucks was no problem at all with the 2100 SM’s integrated conveyor system.

The surface miner cut 80 to 300 m long sections each in four parallel cuts across an overall width of approx. 6.50 m. Depending on the structure, the limestone was cut in several layers at depths of between 20 and 30 cm each. The operation was completed by a 10 cm deep “finish cut”.

Sections of 200 m length each were completed every week, producing an even ground level across the full tunnel width. The ground level produced by the miner permitted the subbase layer applied on the tunnel floor to have a thickness of merely 10 cm, allowing the overall thickness of the concrete slab to be reduced by at least 30 cm.