what is a tunnel boring machine?
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v What Is Tunnel Boring Machine? ü A tunnel boring machine (TBM), also known as a "mole" or a "worm", is a machine used to excavate tunnels . Tunnels are excavated through hard rock, wet or dry soil, or sand , each of which requires specialized technology. ü Tunnel boring machines are an alternative to drilling and blasting (D&B) methods and "hand mining". ü TBMs limit the disturbance to the surrounding ground and produce a smooth tunnel wall. This reduces the cost of lining the tunnel, and is suitable for use in urban areas. TBMs are expensive to construct, and larger ones are challenging to transport. These fixed costs become less significant for longer tunnels. ü TBM-bored tunnel cross-sections range from 1 to 17.6 meters (3.3 to 57.7 ft) to date. Narrower tunnels are typically bored using trenchless construction methods or horizontal directional drilling rather than TBMs. TBM tunn...