Over time, engineers have developed many methods of tunnel construction that make the process more labor-efficient and safer. One such method is the tunneling shield, which was developed in 1818 by British-French engineer Marc Isambard Brunel. Brunel observed how the barnacle’s outer shell allowed it to bore through wood, and he applied this concept to create a giant rectangular cast-iron cavity that could be used to tunnel underground. The tunneling shield worked by resting against the earth, opening steadily to allow workers to dig through the soft soil outside, and pushing the shield face forward with a screw jack. This method led to the first underwater tunnel built under the River Thames in London in 1842. Today, tunneling shields are cylindrical in shape and made from steel, with hydraulic jacks to push the shield forward.
A different challenge arises when digging through underwater rock, which is where modern technology comes into play with the tunnel boring machine (TBM). The TBM revolutionized construction with its rotating cutting head that digs through the rock layer ahead. The machine applies pressure to the rock, causing it to crack, and then conveys the fractured rock away via a conveyor belt. The English Channel tunnel was built using 11 TBM machines to dig 56.3 km long tunnels at a depth of 45 m below the seabed. Another innovative method of tunnel construction is the submerged tube tunnel, developed by American engineer WJ Wilgus. This technique involves building a tunnel from prefabricated pipe sections elsewhere and then submerging and positioning them in a dredged trench in a riverbed or seabed, ultimately burying the structure to restore the seabed.
These various methods demonstrate the evolution of tunnel construction over time, with advancements in technology and engineering leading to more efficient and safer processes. Each method has its own unique challenges and benefits, allowing engineers to choose the best approach based on the specific requirements of the project. Whether using tunneling shields, tunnel boring machines, or submerged tube tunnels, the goal remains the same: to create secure and reliable underground passages for transportation, utilities, and other purposes.