What is the deepest tunnel in the Earth's surface?

I have meet numbers, around 300km.

What is the main problem to make tunnel more deeper? What is the problem with 1000km?


closed as off-topic by tpg2114, Abhimanyu Pallavi Sudhir, John Rennie, Waffle's Crazy Peanut, Qmechanic Nov 5 '13 at 13:28

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    $\begingroup$ Are you interested in the deepest borehole or the deepest structure that most people would call a "tunnel"? The answers differ by more than an order of magnitude. $\endgroup$ – dmckee Sep 26 '13 at 20:43
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    $\begingroup$ The first question could be googled. I think that the last part should be removed. $\endgroup$ – jinawee Sep 26 '13 at 21:13
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    $\begingroup$ Obligatory xkcd: Lakes and Oceans. And if you haven't yet, look up the Kola Superdeep Borehole. $\endgroup$ – Emilio Pisanty Sep 26 '13 at 23:30
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    $\begingroup$ Skeptics mod here, the question would not be appropriate for Skeptics. We require questions to be about notable claims, which this one is not. $\endgroup$ – Mad Scientist Sep 27 '13 at 16:15
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    $\begingroup$ I don't know what you're asserting, but if we are talking about depth and feasibility, 1000km and 300km are insane figures. Wikipedia lists the longest tunnel at 154km (Thirlmere Aqueduct. this is horizontal length), and the deepest borehole at 12km. $\endgroup$ – user12029 Sep 28 '13 at 11:37

The present version of the question is suitable to be asked and answered in the Physics community. We are not able to drill a hole too deep into the Earth for two reasons: temperature and pressure.
Temperature: Look at the temperature profile of Earth, which is copied here. enter image description here
Roughly at 70km deep, temperature is ~1000°C. At this temp, the drill bit, usually made of iron, is too soft to hold its structure, let alone to drill.
Pressure: Again at 70km, the pressure is 20000 atm. 1 atm = 1 kg/cm². For a surface area of 1 m², it's 2 x 10^8 kg of force. No tunnel can be made strong enough to stand it.
Just for the sake of arguing, if we go deeper than 100km, we are about to reach the mantle of the Earth, Mantle is either made of lava or at least semi-fluidic. So, I would say, building a city or a culture inside Earth is a like a pie in the sky.

  • $\begingroup$ Is really the pressure applying like that? I mean, stone is not a fluid, so I expect the ground itself to absorb most of the pressure. $\endgroup$ – Adrian Maire May 15 '17 at 20:21

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