Engineers have devised numerous methods of tunnel construction to streamline the process and improve safety. Among these methods is the tunneling shield, which was discovered by British-French engineer Marc Isambard Brunel in 1818. The shield is a giant rectangular cast-iron cavity that gradually opens to allow workers to dig through the soft soil outside, pushing the shield face forward with a screw jack. The protective shell of the tunnel is built from bricks in the newly carved space behind. This technique led to London’s first underwater tunnel under the River Thames, completed in 1842.
Today, tunneling shields are still used but are typically cylindrical and made from steel. Steel rings support the tunnel and hydraulic jacks push the shield forward. A door allows access to the front of the shield when it’s not moving, while a cover protects workers inside. Another method for tunnel construction is the TBM or Tunnel Boring Machine, which uses a rotating cutting head to dig through rock layers underwater. The fractured rock is conveyed by a conveyor belt, eliminating humans’ need to remove debris manually.
Submerged tube tunnels are constructed using prefabricated pipe sections floated into position and submerged in a dredged trench on rivers or seabeds. The water is then drained from the pipe, and excavated material is used to cover the tunnel, burying it beneath water and restoring seabeds. These methods have significantly revolutionized tunnel construction by making it more efficient and safer for workers than ever before.
