Why don t Underground tunnels collapse?

Because they're stronger that way. Tunnels are circular to take advantage of the characteristics of soil and rock. Soil and rock are resistant to crushing forces (compressive forces). By rounding the ceiling, the weight of the soil and rock from the top to are balanced over the entire tunnel, increasing its strength.



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On October 2, 1925, the tunnel collapsed on a work train, killing four men and trapping a steam locomotive and ten flat cars. Rescue efforts only resulted in further collapse, and the tunnel was eventually sealed for safety reasons. Richmond, Virginia, U.S.

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Collapse of the tunnel isn't what would make it impassible first. The tunnel itself might well last a century or so, but if there's no electric power for as little as a few weeks the tunnel will be closed by water seepage that can't be pumped out.

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About half of the underground lines, in terms of length, are actually on the surface when out of the central area. It is easier and safer to dig at depth in London because of the nature of the soil and to avoid other infrastructure and the Thames.

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Tunnels are circular to take advantage of the characteristics of soil and rock. Soil and rock are resistant to crushing forces (compressive forces). By rounding the ceiling, the weight of the soil and rock from the top to are balanced over the entire tunnel, increasing its strength.

MORE DETAILS