Curved blade cuts tunnel arch

An Italian company has designed a machine mounted with specially made concave diamond sawblades which are capable of forming a perfect curved cut in tunnel archways. This method has been used successfully to create safety alcoves in two road tunnels in northern Italy.

Two types of sawblade blank were manufactured, one 1000 mm diameter for pre-cutting and one 1500 mm diameter to complete the full 650 mm depth. To obtain the required side run out of 0.2 mm for the 1000 mm blade and 0.6 mm for the 1500 mm blade, together with achieving the proper concave shape was very difficult. The blanks were 4 mm thick for both sizes and the steel used was not that used for conventional blanks but of a specification suitable for forming the special concave shape required.

The diamond segments were also specially designed. Segment length was 20 mm and height 8 mm for both blades, with the thickness being 6.5 mm for the smaller blade and 6.0 mm for the larger one. A sandwich type design was used in both segments using 40/50 US mesh high quality diamond grit. This gave good cutting results from the start, but was modified slightly for the first re-tip to achieve even better results.

To maintain a constant depth of cut, the cutting head had to be constantly monitored as it followed the curved surface of the tunnel. At a power of 15 to 20 kW, the machine achieved a cutting rate of 0.8 to 1.5 m2/hr. Peripheral speed was between 40 and 45 m/s.

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