Tunnel Boring Machines (TBM) Information

TTunnel boring machine exampleunnel boring machines (TBMs) are used in subsurface mining operations to excavate tunnels through rock strata and surrounding sedimentary deposits. They consist of a rotating cutting wheel fitted to a series of thrusting mechanisms and conveyors used to advance the machine forward. They can also be referred to as a mole.


Tunnel boring machines are classified as hard rock or soft ground machines. Hard rock TBMs are designed for boring through solid rock and solid aggregate. Soft ground machines tunnel through hydrated soil and unconsolidated sediments, and may be further optimized based on the hydration and stability of intended ground conditions.

Soft Ground TBMs

There are three types of soft ground TBMs: earth pressure balance (EPB) machines, slurry shield (SS) and open-face type. Both slurry shield and earth pressure balance types use thrust cylinders to advance forward. Additives such as bentonite, polymers and foam can be injected ahead of the cutterhead to increase the stability of the ground. Additives can also be injected in the extraction screw to ensure that the cut material remains thick enough to provide a plug in the screw to maintain pressure within the cutterhead.

Hard Rock TBMs

Hard rock TBMs use disc cutters mounted in the machine cutterhead. Aggressive disc cutters create compressive stress fractures in the rock, causing it to chip away. The fractured rock, known as muck, is transferred through openings in the cutter head to a conveyor or to muck cars for removal from the tunnel.

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Rama / CC BY-SA 2.0 FR