When I was in kindergarden digging holes in the sandpit, I used to wonder how deep a hole I could dig.
So, with today’s technology and lots of labor and resources, how deeply could I go into the Earth? What would it entail?
The Great GOOGLE knows all!
And the Great GOOGLE tells me that the Wikimind may help you:
That only answers how deep the Russian’s went in 1989 (12 km).
How deep could we go using the best technology if money was no object?
I hope the OP won’t mind if I spice it up. An alien race buries a hypernova bomb 100 km deep in the upper mantle. We have 1 year to reach it and defuse it.
Can we do it?
Back in the '60s there was a US project to dig to the Mohorovičić discontinuity, between 5-10 kilometers beneath the ocean, which is the point at which the Earth’s crust really stops behaving like crust, and really starts behaving like mantle, although a sharp transition seems unlikely.
The project was not successful, it is technically a lot more complicated that just dig and keep on diggin’:Project Mohole - Wikipedia
We do keep trying 'tho. Chikyū - Wikipedia
I can’t help but wonder, if we actually dug through the Earth’s crust, wouldn’t that release mantle material in some sort of supervolcano? What’s left to hold the mantle down?
Well, I’m no geologist but the thinnest point in the Earth’s crust (the oceanic crust, i.e. the bottom of the ocean) is roughly 6 miles thick. The continental crust is another 14-24 miles thicker. The mantle which, as is my understanding, is mostly solid, is about 1,800 miles thick. Beneath that is the liquid outer core in which I would assume a drill or any other digging/boring equipment is useless.
So I’d say about 1,800 miles would be the absolute maximum, give or take a few.
How far we could actually get, I have no idea.
Someone please correct me if I am wrong about any of that (and I’m sure someone will).
In America, Earth Science bores you. In Soviet Russia, Scientist bore Earth!
Nope. Even with Bruce Willis.
Given unlimited time and money probably yes. But a year gives us no time to develop new technology. Everything would have to be done with off the shelf gear, and that simply isn’t going to happen.
Current drilling technology simply doesn’t drill down fast enough. Depends greatly upon what you are drilling through, but even with easy strata, drill rates are going to be an order of magnitude too slow.
Temperature. It is simply too hot at depth for off the shelf techniques to work. A drill rig works by pumping fluid (mud) down the centre of the drill pipe. The mud flow is used to power the drill head, and to sweep the pulverised rock the drill head has ground off up to the surface.
Just the frictional losses of 100km of drill pipe are going to mean that you need new technology. But even if it can be made to work you have many more problems. At more than a few tens of km down the temperature is going to exceed the useful working temperature of any conventional (or indeed unconventional) mud. Muds are actually reasonably sophisticated, but are either water or oil based. In either case you will have mud reaching temperatures vastly higher than their useful working temperatures. At depth they won’t boil (although when they reach the surface again you will have quite a problem). But oil based muds will probably decompose, and at high temperatures and pressures water becomes an astoundingly corrosive material that will tear into your drill pipes. You will be in the province of geochemical forces. Conventional high strength steels are past their useful working temperatures, so as you get deep you will need to employ more exotic materials. Special stainless steels will work, but if you are unlucky you may have to resort to other metals at the deepest part of the hole. At insane cost. There are no off the shelf solutions, so all custom engineering with significant lead times for development, tooling and manufacture. Working out how to make a drill work, and stay working, in temperatures 500 to 1000 Celsius isn’t going to be trivial.
Conventional drill systems are not designed to get that deep anyway. One of the limiting issues is the need to case a hole if you are in strata that is not stable. If you are drilling through something soft, fractured, or weak, the hole may try to collapse on you. The solution is to run a steel liner into the hole. This holds the hole open and you can keep drilling past the problem. Where you get into trouble is the next time you have the same problem. You will need to run a new length of casing. But it needs to fit past the first length you used. So it is of a smaller diameter. Wells are drilled like this all the time, and they start with a quite wide diameter, and as the hole gets deeper, its gets narrower, each time they have to case the hole. There are standard sizes to all the well casings, and drill bits, and it is a standard procedure. But eventually you run out of diameter. Oil wells are abandoned simply because they reached the minimum hole diameter. And that can happen only a few km down.
Oil wells tend to be drilled into strata where finding oil is the priority. So if the goal is to drill to depth alone, there is the freedom to try to find a location where it is known that you will find the least number of problems on the way down, and can avoid casing the hole as much. But if the alien bomb is the goal, you may not have quite that luxury. At great depth the strata may well be more stable, so once past the worst things may improve.
Just the logistics of drilling at depth are a problem. It takes a few hours per kilometer of drill pipe to pull a drill string out of a hole. You need to do this whenever you have a problem. For instance to repair or replace a drill. You are running in and out of the hole a number of times if you have to case the hole. With 100 kilometer deep hole it could take two weeks just to replace a drill bit for no other reason than this is how long it takes to pull the drill out and put it back. You may easily find that an entire year could be lost to just the time used up running into and out of the hole, with no time left for actually drilling.
No reason that oil well drilling systems could not be modified and new technology eventually successfully deployed. But the oil industry is already one of the richest and most focussed in the world. They spend astounding amounts on developing drilling technology, and almost unimaginable amounts of money actually drilling.
Ten years and ten billion dollars might do it. But even with 100 billion dollars you wouldn’t do it in a year. There is a lot we don’t know about things that happen at depth, so almost anything might turn up to totally derail the project.
The fate of the earth is in the balance…
Suppose we string Nukes at 500 meter intervals for 10 km down, detonate them in a chain, drop down a riser into the cavity before it collapses inwards, then use that to dig down the next 10 kilometers, drop another 10 nukes down at 500 meter intervals. Rinse… repeat. 
Arne Sacnussem?
This isn’t a video game or a junior high science fair project. Those bombs are all detonated at or above the mudline, which is different than trying to make them work at the bottom of a deep wellbore.
At those depths, the temperature is high enough to fry all the electronics in the bomb. I’ve got an engineer friend working for Halliburton and her job is to figure out how to design electronic components that will survive in a drilling situation at 300-400 degrees. Most, it involves some ridiculously expensive components and serious engineering to get a simple circuit board to function. I suppose you could re-work this stuff in the bombs, but it would still take the better part of a year, if not longer.
Besides which, you have to string physical control cables to the bombs (you don’t really think we can remote detonate the bombs under all that rock, do you?) or devise another method for figuring out how to tell the bombs to explode. An actual cable is contra-indicated by the explosion.
So, how? Timing? That requires everything go perfectly right.
Depth monitoring? Below the earth, our notion of ‘depth’ relies on physical measurement along the wellbore, as pressure increases are not a reliable gauge. The bomb itself wouldn’t be able to determine its own depth without an outside signal (again, see above problems with getting signals to bombs several km below the surface).
Maybe you were joking, but this suggestion is not much better than suggesting you simply get 1 million people to each dig 1m one after the other.
With that sort of funding I bet you could simply walk into Mordor.
How deep could you go if you just litteraly dug a cone shaped hole rather than a fancy borehole? Think a something like an open pit mine, just absurdly bigger. You could take a WAG at how many people you could have working at the mine, how you dig up and drive around on hot assed rocks and so on and so on. Probably couldnt get very far in a year, but if time wasnt an issue you might be able to get pretty deep eventually.
I larfed.
I think you mean yummy nougat don’t you? 
Obviously, we can dig all the way to the bottom.
As Bill Bryson has put it in his Short History of Nearly Everything, in the end it came to be called the “No Hole”.
Fun facts from freshman fysics:
If you dug a hole straight through the center of the earth and out the other side, and jumped in, you would emerge at the other side in about 42 minutes, and your speed would be zero mph at that point, so you could just step onto the earth there, assuming you had the gymnastic ability to either walk on your hands, or do a half flip during the trip.
If you didn’t step off, you would oscillate back and forth between the two entrances indefinitely, 42 minutes for each one-way trip.
And if you had dug the hole in some other direction, i.e. straight but off-center, so it came out somewhere not at the end of the diameter you were standing on, the time to jump through would still be 42 minutes, even for very shallow angles.
And (back to the straight through the center hole) if you got the Mythbusters to fire a cannonball horizontally from the point you jumped, two seconds after you jumped, at the exact speed needed to orbit the earth an inch off the ground, you would see the cannonball 1 second away from you every time you popped up on either side.
Of course, all of the above assumes no air, no enormous heat, no friction with the sides of the hole for the off-center cases, no rotation, perfect sphere with no buildings or trees to interfere with the cannonball, etc.
Relevant thread from about a month ago: Let’s say I drill a hole through the Moon, and drop a golf ball into it
One of the conclusions of the “peaceful nuclear explosions” programs was that nuclear explosions don’t really work all that well for excavating in the subsurface.
The trouble is that as the depth and lithostatic pressure increases, it takes a lot more energy to melt rock, which means that the size of the cavity made goes down. By the time you got past the depths drilled by conventional means, detonating a nuclear bomb down there wouldn’t really do much.
But I, like my dog with his bone, want simply to dig a hole to China, as is commonly said.
I live in NYC. Which way do I go?