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 mountain material is solid and strong enough not to collapse the hole, or the hole is lined with reinforcement that transfers load from one side to the other. This is now iron/steel rings or reinforced concrete. Tunnel boring machines build the liners as they progress, and push forward using the last ring.
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.
The first tunnel built whose engineer is known was excavated in the island of Samos. The engineer Eupalinos de Megara, built this tunnel in the 530 b.C to supply with water the capital of the island and was, with its 1 km length, considered as one of the three marvels of the helenic world.
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.