Channel Tunnel Boring Machine

The 1,100-tonne mole that chewed through chalk under the sea/Engineering Marvels

The Channel Tunnel was bored by 11 tunnel boring machines (TBMs), with the largest being the marine service tunnel machines at 8.36 meters in diameter. Each TBM weighed about 1,100 tonnes and could advance up to 75 meters per day through the chalk marl beneath the English Channel. The TBMs that bored from the English side were driven forward into the ground and buried in place when they completed their runs, as it was cheaper to buy new ones than to extract them. They remain entombed beneath the sea bed to this day.