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...Types of tunnels construction methods a mountain tunnel drilling and blasting d b method natm new austrian tunneling is the most common it originates in hard rock utilizes rockbolts shotcrete applied immediately after this often followed by cast situ concrete lining using formwork boring machine tbm tmb used as an alternative to tbms are excavate with circular cross section through variety subterranean matter sand or almost anything between moves forward round cutter heads cut into face splits off large chunks head carves smooth hole exact shape conveyor belts carry shavings out back dumpster wall consists precast segments that form rings shallow buried soft soil cover type if under water immersed tube deep excavated tunnelling shield for intermediate levels both possible where trench roofed over strong supporting beams necessary avoid danger collapsing uses one two shields metal cylinder ground rotating cutting wheel located at front end behind chamber depending on either mixed slurry...