subaqueous tunnel

A subaqueous tunnel is a horizontal underground passageway constructed beneath a body of water. These tunnels are primarily used for transportation, such as carrying road vehicles, trains, and subways, as well as for conducting water and sewage.1

There are two main engineering methods for constructing subaqueous tunnels:

• Shield Tunneling: This method involves using a protective shield to excavate the tunnel. Initially, compressed air was used to hold back water pressure, but this posed significant risks. Modern shield tunneling often involves miners working in individual pockets within the shield, which is propelled forward by jacks. Permanent lining segments are erected under the shield's protection.2
• Immersed-Tube Tunnels: This technique involves prefabricating long tube sections, floating them to the site, sinking them into a dredged trench, and covering them with backfill. This method is often preferred as it allows interior work to be done at atmospheric pressure, avoiding the risks associated with high air pressure.3

The immersed-tube method is suitable for deeper water than shield tunneling and has become a frequent choice for subaqueous crossings.43