A tunnel boring machine (TBM) also known as a `mole`, is a machine used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They can bore through anything from hard rock to sand. Tunnel diameters can range from a metre (done with micro-TBMs) to 19.25 m to date. Tunnels of less than a metre or so in diamet.....
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http://en.wikipedia.org/wiki/Tunnel_boring_machine
A machine used to excavate a tunnel through soil or rock by mechanical means as opposed to drilling and blasting.
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https://www.encyclo.co.uk/local/22734
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