- tunnels and underground excavations - Encyclopedia Britannica
Tunnels and underground excavations, horizontal underground passageway produced by excavation or occasionally by nature’s action in dissolving a soluble rock Tunnels have many uses: for mining ores, for transportation—including road vehicles, trains, subways, and canals—and for conducting water and sewage
- How Tunnels Work - HowStuffWorks
In long tunnels, vertical shafts may be dug at intervals to excavate from more than two points Now let's look more specifically at how tunnels are excavated in each of the four primary environments: soft ground, hard rock, soft rock and underwater Soft Ground (Earth) Workers dig soft-ground tunnels through clay, silt, sand, gravel or mud
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