Hey! I'm in the midst of writing some sci-fi and would like some geological help on a concept I've been playing with.
Basically, the story takes place in an underground city. A little bit like The Matrix series, I know (well okay, a lot like it), but what I wanted to know was what sort of rock would be the best for such an undertaking? Where would the best area in the world be for it? How deep would the changes in rock be, and how would those changes affect things?
If these questions need clarification, please don't hesitate, and let me know too just how plausible the idea is (if it's impossible, what would we need to do to make it possible?). I know next to nothing about geology but it plays a significant role in the story.
In the story, the city is enormous and must be self-contained, all exits sealed, do not open until christmas 3030 sort of deal.
Any help at all would be greatly appreciated. Thanks!
the location of your city would be useful. will it be on earth? where? if not what is the country it is in like? mountains? flat plains?
how deep? how many ppl?
Also, if all entrances are sealed - how would you be able to create new room? it ims completely impossible because you need a place to dump the excavated rocks. if there are no ways to get out you city cannot grow and will choke in its own waste.
Yes, it's on Earth, so I would need a plausible earthly location. I'm guessing in a moutainous region? Doesn't need to be, but it comes to mind.
Very deep. As deep as would humanly be possible to go without having the entire thing collapse in on itself. Therefore, the city viewed from the side would look like a sideways eye, or maybe a teardrop. In the context of the story, humanity has about twenty years to focus all of its manpower and resources into building it.
The sealing of the exits was for two purposes: first, keeping whatever's outside from getting in, and second, to eventually force humanity to have to leave, because of a total lack of resources. The plot centers around peopl with a vested interest in keeping everyone in.
Actually, regarding space and waste, what if they had access to a large network of empty caverns?
actually if this is artificially created (i am not miningn or tunnelling engineer) i would rather not chose an active mountain range. earthquakes and movements of the rocks could be severe dangers. The very deepest man-made mine to this day is in south africa and is about 4.000m below surface at the deepest point. the deepest drill hole ever made is in russia and roughly 12km deep. these might give you some natural limitations.
also, with depth, temperature will increase by 3C for every 100m on average. of course this is influenced by the presence or absence of geological factors like volcanoes. i would think a stable and old craton would have a very low gradient and close by volcanoes would give you a high one.
you need to keep in mind in a depth of 1.000m this would give you 30C. you need some cooling system otherwise your ppl wil be cooked alive in 2.000 m might be 60C. no one can live there unless you have an active cooling and ventilation.
you wouldnt be able to make a huge cavern like you want. there is a limit to rock stability caused by the rheology of the rocks, the presence of cracks and faults and other factors. i think it might be easier to make long tunnels with big diameter (lets say 20m to 40m) than one huge cavern with hundreds meters in diameter.
then again your construction time...well...i do not know how big you really want it. but just remember how long it took to build the tunnel thru the channel from france to britain. but lets assume building it, whether as tunnels or cavern, wont be a problem.
you need a way to the outside for simple reasons: dewatering the cavern, air to breath (nuclear fallout bunkers use special filters to filter out radioactivity from the air btw) and a place to dumb new excavated rocks. it is simply un-economical in my view to have extra free space just to dump your waste. actually an exisiting way to get out like thru the ventilation might add a nice aspect to your story. ;)
I had no idea the temperature change would be so severe, so fast. This will make an excellent plot device.
Regarding the stability, would it be possible to maintain structural integrity artificially? I.e., with a massive infrastructure of some metal? Having it as a series of tunnels would still work in my story, as long as there is one long vertical one that spans from top to bottom.
For the dumping of rocks and the like, when the story starts (and in the background of the city's construction) the city itself is already completed and meant to remain static. Obviously, this causes problems with overpopulation, but that was intentional. However, I am neither against having a ventilation system to the outside world since I can't think of another way to recycle the air. Would it be too much of a stretch to have greenhouses with trees?
Also, thanks for all your feedback! This is really useful so far.
Yeah the temperature can rise pretty quickly. I.e. in northern Germany is an athrazite mine of around 1.500 m deep. In the lowest point the temperature is 40 to 45C and 100% air humidity(from machines, from rocks, exhalated breath and other sources) - and that's WITH active cooling and ventilation. Without no miner could work down there.
Yes, to some degree you can stabilise the rock by technical means like rock anchors, shotcrete, wodden or steel beams, etc. Of course if this is sci-fi you could have some very strong stells but I can't help you with those. Some rocks are stable without any supporting structure but this is highly dependent on the presence of cracks and faults and the kind of rock you have. With depth it will become more and more difficult to suppurt large caverns (increasing pressure of the rocks that are on top).
greenhouses? i have no idea how much room, air, soil and energy you would require for those. i dont doubt you can make greenhouses underground but i have no clue if it would be useful except for maybe parks or sport areas.
Depends what you mean with the greenhouses. They could be on the surface linked via tunnels, or they could be entirely underground with artificial lighting as in the 1972 movie Silent Running (except that was set in space). For this option you'd need to calculate the oxygen production from a given area of woodland and the oxygen requirement for a given populous.
Alternatively you could incorporate the source of a large part of present day oxygen production - diatoms.
Rank: Gypsum
Joined: 12/07/2007
Points: 54
the location of your city would be useful. will it be on earth? where? if not what is the country it is in like? mountains? flat plains?
how deep? how many ppl?
Also, if all entrances are sealed - how would you be able to create new room? it ims completely impossible because you need a place to dump the excavated rocks. if there are no ways to get out you city cannot grow and will choke in its own waste.
Rank: Talc
Joined: 29/09/2007
Points: 3
Sweet! Questions! Alright, let's see then...
Yes, it's on Earth, so I would need a plausible earthly location. I'm guessing in a moutainous region? Doesn't need to be, but it comes to mind.
Very deep. As deep as would humanly be possible to go without having the entire thing collapse in on itself. Therefore, the city viewed from the side would look like a sideways eye, or maybe a teardrop. In the context of the story, humanity has about twenty years to focus all of its manpower and resources into building it.
The sealing of the exits was for two purposes: first, keeping whatever's outside from getting in, and second, to eventually force humanity to have to leave, because of a total lack of resources. The plot centers around peopl with a vested interest in keeping everyone in.
Actually, regarding space and waste, what if they had access to a large network of empty caverns?
Rank: Gypsum
Joined: 12/07/2007
Points: 54
actually if this is artificially created (i am not miningn or tunnelling engineer) i would rather not chose an active mountain range. earthquakes and movements of the rocks could be severe dangers. The very deepest man-made mine to this day is in south africa and is about 4.000m below surface at the deepest point. the deepest drill hole ever made is in russia and roughly 12km deep. these might give you some natural limitations.
also, with depth, temperature will increase by 3C for every 100m on average. of course this is influenced by the presence or absence of geological factors like volcanoes. i would think a stable and old craton would have a very low gradient and close by volcanoes would give you a high one.
you need to keep in mind in a depth of 1.000m this would give you 30C. you need some cooling system otherwise your ppl wil be cooked alive in 2.000 m might be 60C. no one can live there unless you have an active cooling and ventilation.
you wouldnt be able to make a huge cavern like you want. there is a limit to rock stability caused by the rheology of the rocks, the presence of cracks and faults and other factors. i think it might be easier to make long tunnels with big diameter (lets say 20m to 40m) than one huge cavern with hundreds meters in diameter.
then again your construction time...well...i do not know how big you really want it. but just remember how long it took to build the tunnel thru the channel from france to britain. but lets assume building it, whether as tunnels or cavern, wont be a problem.
you need a way to the outside for simple reasons: dewatering the cavern, air to breath (nuclear fallout bunkers use special filters to filter out radioactivity from the air btw) and a place to dumb new excavated rocks. it is simply un-economical in my view to have extra free space just to dump your waste. actually an exisiting way to get out like thru the ventilation might add a nice aspect to your story. ;)
Rank: Talc
Joined: 29/09/2007
Points: 3
I had no idea the temperature change would be so severe, so fast. This will make an excellent plot device.
Regarding the stability, would it be possible to maintain structural integrity artificially? I.e., with a massive infrastructure of some metal? Having it as a series of tunnels would still work in my story, as long as there is one long vertical one that spans from top to bottom.
For the dumping of rocks and the like, when the story starts (and in the background of the city's construction) the city itself is already completed and meant to remain static. Obviously, this causes problems with overpopulation, but that was intentional. However, I am neither against having a ventilation system to the outside world since I can't think of another way to recycle the air. Would it be too much of a stretch to have greenhouses with trees?
Also, thanks for all your feedback! This is really useful so far.
Rank: Gypsum
Joined: 12/07/2007
Points: 54
Yeah the temperature can rise pretty quickly. I.e. in northern Germany is an athrazite mine of around 1.500 m deep. In the lowest point the temperature is 40 to 45C and 100% air humidity(from machines, from rocks, exhalated breath and other sources) - and that's WITH active cooling and ventilation. Without no miner could work down there.
Yes, to some degree you can stabilise the rock by technical means like rock anchors, shotcrete, wodden or steel beams, etc. Of course if this is sci-fi you could have some very strong stells but I can't help you with those. Some rocks are stable without any supporting structure but this is highly dependent on the presence of cracks and faults and the kind of rock you have. With depth it will become more and more difficult to suppurt large caverns (increasing pressure of the rocks that are on top).
greenhouses? i have no idea how much room, air, soil and energy you would require for those. i dont doubt you can make greenhouses underground but i have no clue if it would be useful except for maybe parks or sport areas.
Rank: Apatite
Joined: 31/12/2004
Points: 606
Depends what you mean with the greenhouses. They could be on the surface linked via tunnels, or they could be entirely underground with artificial lighting as in the 1972 movie Silent Running (except that was set in space). For this option you'd need to calculate the oxygen production from a given area of woodland and the oxygen requirement for a given populous.
Alternatively you could incorporate the source of a large part of present day oxygen production - diatoms.
Hope this helps.
Ben.