Civil Engineering

Question

How do you build a tunnel under water without it leaking while it is under construction?

Answer

There are two very different ways of building tunnels under water: 1) Start on dry land near the water, and dig down and over, staying deep enough to stay in solid rock under the water. Some water will usually seep in, but you try to have big enough pumps to keep the work site dry. Lining the tunnel with concrete is sometimes done to reduce the amount of water leaking in. If there are cracks in the rock, sometimes they are sealed by drilling a well into the crack, then pumping in grout, which is a special kind of concrete that flows into cracks and then hardens. There is always the danger of big leaks. 2) Some tunnels are built by digging a ditch in the muddy bottom of the bay or river, then sinking large pipes into the ditch, joining them end to end to make the tunnel, then covering the pipes to fill up the ditch. Finally the water inside the pipes is pumped out, leaving a dry tunnel. You may need divers to work underwater to connect the pipes.