• Question: How do you build bridges under the water without the water entering

    Asked by 256prdq24 to Noel, nina, Ivan, Gowthaman, Diana, Alice on 8 Mar 2019.
    • Photo: Alice Selby

      Alice Selby answered on 8 Mar 2019:

      There are a couple methods to build tunnels, but the water will enter and later be pumped out.

      Some tunnels are made with TBMs.

      Builders dig a trench in the riverbed or ocean floor. They then sink pre-made steel or concrete tubes in the trench. After the tubes are covered with a thick layer of rock, workers connect the sections of tubes and pump out any remaining water.

    • Photo: Ivan Merrick

      Ivan Merrick answered on 11 Mar 2019:

      A bridge under water is generally called a tunnel. It is the same function as a bridge as it connects two pieces of land a distant apart. Alice gave a great answer and gave you a link to a video. A TBM is a Tunnel Boring Machine. These were use to bore the Channel Tunnel which connects Britain and France and through which trains ferry cars truck and people from London to Paris every day.

      Another method of building tunnels underwater is to construct a concrete hollow box section on land. These would be tens of feet in length. The number of sections built would be sufficient to reach from dry land to dry land across the stretch of water.
      The ends of the box are plugged with a steel wall with gates in them.The sections are floated on barges out to the correct point on the water and sunk to the bottom with the gates open. The sections are tied down to the ocean floor and joined to each other until the tunnel reaches dry land on either end. When all the section are in place, the gates on each section ends are closed and the water pumped out until the tunnel is dry. When all the water has been removed, the section walls are cut out to give you the complete tunnel.
      Unfortunately it is not possible to build a tunnel under water without some water leaking in. In fact pumps are permanently installed in the tunnel after it is finished because there is nearly always water leaking into the tunnel.

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