Tunnel Boring Machine (TBM)

Definition - What does Tunnel Boring Machine (TBM) mean?

A tunnel boring machine (TBM) is a piece of equipment designed to bore circular tunnels through dense, hard rock, relatively soft sand or any substrate of any hardness between the two. They come in various sizes capable of creating bores with diameters as small as 40 inches and as large as 60 feet.

A tunnel boring machine may also be referred to as a mole.

Trenchlesspedia explains Tunnel Boring Machine (TBM)

In the past, mining and other underground work was done by drilling and blasting. The tunnel boring machine changed all that. Its ability to produce a smooth, directional tunnel while leaving surrounding rock relatively undisturbed was superior to blasting, which could cause cave-ins. The smooth tunnel wall meant lower ongoing costs because the tunnels didn’t require a tunnel liner. The TBM created tunnels significantly faster than steam drills or a pick, shovel and ore cart. In fact, the only disadvantage was the upfront cost of purchasing one of these subterranean marvels.


In terms of trenchless work, particularly in an urban environment, the TBM must have positive face control, a system that allows the TBM to control the subsidence of the ground above the trenchless installation.


Regardless of the project, when a tunnel boring machine is needed, careful planning and a thorough geological investigation into substrate types, including bores, stress testing and ground penetrating radar surveys should be conducted early in the planning stages of the project.

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