Tunnel boring machines are used as an alternative to drilling and blasting (D&B) methods in rock and conventional “hand mining” in soil. TBMs have the advantages of limiting the disturbance to the surrounding ground and producing a smooth tunnel wall. This significantly reduces the cost of lining the tunnel, and makes them suitable to use in heavily urbanized areas. The major disadvantage is the upfront cost. TBMs are expensive to construct, and can be difficult to transport. The longer the tunnel, the less the relative cost of tunnel boring machines versus drill and blast methods. This is because tunneling with TBMs is much more efficient and results in shortened completion times, assuming they operate successfully. Drilling and blasting however remains the preferred method when working through heavily fractured and sheared rock layers.