How do tunnels not 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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Although this is also seen to a certain extent in bridges, it is not to the extent seen in tunnels. Events such as earthquakes and floods, which are the major causes of collapse of other structures, account for only about 10% to 20% of all tunnel collapses.

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Underground structures last a significantly longer life time than above-ground structures. Approximately about 50 years for above-ground, over 100 years for tunnels.

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The alignment of a tunnel constructed from two ends and meeting somewhere is the middle is achieved via old fashioned surveying methods. If the tunnel breaks through to the surface, surveying stations are accurately established on the surface of the Earth at each end of the tunnel.

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The Laerdal Tunnel in western Norway is the longest road tunnel in the world. It takes about 20 minutes to pass through the tunnel. Brightly colored lights placed every six kilometers help drivers stay alert.

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In cooperation with Rönesans Holding, the Heitkamp Construction Swiss GmbH tunnel and railroad construction specialists constructed the world's longest and deepest tunnel, the Gotthard Base Tunnel. This 57 kilometre-long tunnel lies at a depth of 2,300 metres.

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Accidents in tunnels are more dangerous than in the open air. An explosion or fire may cause considerable damage and hazardous substances cannot be removed quickly. Smoke causes poor visibility, lack of oxygen rapidly occurs and there may be panic. It is difficult to escape from a tunnel.

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