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Tunnel boring machine - ø 3 - 15 m
Robbins Main Beam TBM has a complex design but uses a very easy concept. These are ideal for rocks with competent to slightly fractured formations. Machines can be designed to suit tunnel specifications in diameters ranging from 3 to 15 m or 10 to 50 ft. The tunnel diameter is matched by a rotating cutterhead, which is the TBM’s front. Disc cutters, with diameters ranging from 11" to 20", are held by the cutterhead. The cutters are placed to ensure perfect boring of the rock type. Upon turning of the cutterhead, the cutters are pushed into the rock by hydraulic propel cylinders. When this high thrust is transferred via the rolling disc cutters, it leads to fractures of rock. This leads to breakage of chips away from the tunnel face.
As the propel cylinders extend, a floating gripper is pushed on the sidewalls and is locked in place. This enables advancing of TBM by the main beam. Continuous steering of the machine is possible when gripper shoes are pushed on the sidewalls to react the forward thrust of the machine.