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The deepest mine 3580 meters (2.2245088682096554 miles)
below surface at the East Rand mine
technology is constantly improving and the South mine is currently being deepened to 4.1km. The Western Ultra Deep Levels, affectionately known as
'Wuddles', is planned to go down 5km in the next few years.
The Radius of the Earth is approximately 6371 km or 3956 miles so our 2.5 mile deep mine is 0.063% (about 1/200th) of the way.
the miners have to work in high temperatures , more than 50C or 122F
The temperature of the earth's crust increases downward at about 30°C for every kilometer of increased depth
That means a 3 kilometer deep mine might reach temnperatures of nearly 100 C (nearly the boiling point of water. Human body temperature is 37°C and so
once you are deeper than a kilometer or so, the air in the tunnels must be cooled.
The pressures created by the weight of overlying rocks also increase significantly with increasing depth. The pressure in the rocks goes up by 300
bars for every kilometer increase in depth (atmospheric pressure at sea level is 1 bar). A person in a tunnel would not experience this pressure
directly, as the pressure in the air in the tunnel is only affected by the weight of the air above the person, not the rock. Air pressure would go up
with depth, but much more slowly. However, as the rock pressure goes up, the walls of a tunnel begin to experience very large forces, which can lead
to partial collapse of tunnel walls or ceilings (called rock bursts). Rock bursts and tunnel stability become important problems at depths of several
kilometers and are well known in deep mines.
If the engineering problems are overcome, a more fundamental lower limit of tunnel depth is imposed by a change in the physical properties of rocks,
which occurs from about 10 to 20 km depth, depending on local conditions and rock type. At those depths, rocks begin to flow plastically, like taffy,
and any opening would slowly squeeze shut. The flow is temperature-sensitive very slow at the top of the plastic zone (about 350 C), but would become
faster as temperature increased (toward 500-600 C).
David Smith, Geology and Environmental Science La Salle University, Philadelphia, PA