When the dimensions of the tunnel being dug do not make the use of a special machine with gathering system essential, the job can be done using an ordinary excavator fitted with a cutting system instead of the ordinary bucket boom.
Obviousily, excavated debris are removed using a separate machine.
Compact in-line cutting units can be used on materials having a compressive strenght up to 500 daN/cm².
These cutting units have greater penetration capacity in hard terrains and provide better tunnel shaping, especially for horse-shoe tunnels.
The excavator weight must be appropriate to cutting group power.
For in line cutting boom, which are generally used on harder materials, the excavators must be heavier: at least 24 tons for power up to 75 Kw ; at least 50 tons for powers from 76 to 132 Kw.

Rotation System with Hydraulic Jacks

The excavators used for these applications are prepared with slew powered by hydraulic jacks instead of the slewing-ring and pinion system.
This modification is of fundamental importance since it eliminates the backlash between pinion and slewing-ring, which causes impacts and vibration on the boom during excavation.
Moreover, the forces involved in cutting are too high for the pinion and slewing-ring system.

OPTIONAL

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