Tunnel boring machines were used to bore sand out of a water body, giving a chance to the manual labors to simultaneously fill the area with cement and build walls around the dug up area. This way they were able to stop the flow of water and take out excess water from the tunnel area for the further building process.
Nowadays, more advanced technologies are used to build an underwater tunnel which gives the builders a chance to perform several processes of digging up of soil and filling the area with cement and steel simultaneously in order to complete the work in a record time. The most common method involves digging up of a trench in the seabed or river bed. Then the related building material such as steel and cement is sunk into this water bed and any excess water is taken out by use of heavy duty pumps. This process is carried out in many phases and finally, the different parts are connected together to form a tunnel.
Although the underwater tunnel involves a great amount of time and labor but the purpose they serve outnumbers all these constraint factors. Imagine a world without these tunnels. How much time would humans have lost in crossing the riverbeds by boats and ferries?
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Instead, these tunnels even act as a medium to transport materials and people along with other services like ferries and boats which often pass over them. Moreover, the time they save can never be neglected by looking at the various feasibility options available in waterborne transports nowadays.