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Author Topic: How can a 350 meter wall support itself?  (Read 7111 times)

Offline Voxx

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How can a 350 meter wall support itself?
« on: 14/08/2013 07:59:00 »
Alright guys!  Another SF question!!

If I have a huge 350 meter high wall that can be made of of any substance (man known), how can it stand with these questions.

How thick does it need to be?

It can be made from multiple different substances (reinforced concrete, marble, hell obsidian).  I'm guessing that steel would probably be a good support.  Anything is really up for grabs though (that is reasonable).

This wall has stood for over two hundred and fifty years in a heavy moisture area (very foggy and by the sea).  So that'll narrow down the material a bit.  There's also slight volcanic activity around the area.

Maintenance is a must, but will be different with whatever material you guys come up with.

It also needs to be sleek and flat (although, a slight tilt is acceptable).

If it were the real world, consider constructing it with no expense cost.  Money is no objective.

I wonder if it's even possible to engineer!  =p


 

Offline CliffordK

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Re: How can a 350 meter wall support itself?
« Reply #1 on: 14/08/2013 11:23:48 »
One option might be to construct the "wall" out of a mountain range.  No doubt it would not be monolythic, but one might use a mix of carved stone and concrete, with the fill materials recovered from the carving the mountains.  Is the wall one sided, or two sided?

Perhaps your project would share a lot with dam construction, some are in the range of 300M tall.

Wind would certainly be an issue as one wouldn't want the whole wall to blow over.

The St. Louis Arch is built out of welded stainless steel panels, I believe with the panels themselves providing the support structure for the arch.  I could imagine building a wall out of solid stainless steel panels.  One might choose some kind of a honeycomb design to provide adequate cross linking.

Stainless, or even thick mild steel, would provide an excellent facing for a concrete & earthen structure.

WATER may be an issue.  If one chose the continental divide (Rocky Mountains in the USA) for building the wall, then one could plan it to have no water penetrations.  Otherwise, there might be a need for rivers to flow trough or under the wall, perhaps through a tunnel. 
 

Offline Pmb

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Re: How can a 350 meter wall support itself?
« Reply #2 on: 14/08/2013 11:49:13 »
One option might be to construct the "wall" out of a mountain range.  No doubt it would not be monolythic, but one might use a mix of carved stone and concrete, with the fill materials recovered from the carving the mountains.  Is the wall one sided, or two sided?

Perhaps your project would share a lot with dam construction, some are in the range of 300M tall.

Wind would certainly be an issue as one wouldn't want the whole wall to blow over.

The St. Louis Arch is built out of welded stainless steel panels, I believe with the panels themselves providing the support structure for the arch.  I could imagine building a wall out of solid stainless steel panels.  One might choose some kind of a honeycomb design to provide adequate cross linking.

Stainless, or even thick mild steel, would provide an excellent facing for a concrete & earthen structure.

WATER may be an issue.  If one chose the continental divide (Rocky Mountains in the USA) for building the wall, then one could plan it to have no water penetrations.  Otherwise, there might be a need for rivers to flow trough or under the wall, perhaps through a tunnel. 
Great stuff CliffordK!!

The fact is that one needs to know the exact material in oder to know how high it can be made and what the environment is. The height of the wall does not depend on the thickness though. The strength of the material is what determines how much stress it can take when something like wind is beating on the side. The width will determine how much of that it can take too.
 

Offline Phractality

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Re: How can a 350 meter wall support itself?
« Reply #3 on: 15/08/2013 04:50:30 »
Strength to density ratio is what matters most. Single-walled carbon nanotubes have the greatest strength to density ratio known to man; they just aren't yet available in the quantities you're looking for.

Strength is measured in units of pressure. How much pressure is needed to crush it? The pressure at a given height is equal to the weight of what's above that height divided by the cross section area. Each layer must support the weight of everything above it, so the bottom must be thickest.

This problem is similar to the space elevator problem; the difference is compression vs. tension. In tension, each level must support the weight of what is below it, rather than above it. Tensile strength tends to be roughly the same as compressive strength, so the thickness should be roughly the same. A space-elevator cable which is 1 cm thick at the base would be only slightly more than 1 cm thick at 350 m.

In compression, you have to be concerned about buckling and toppling, so you need your wall to be wavy or zigzag, rather than straight; that will give it horizontal rigidity to resist wind and earthquakes. You could also get rigidity by casting your wall sections in a honeycomb fashion, making the wall thicker, but the same weight.

So if you are using single-walled CNT, the weight of the wall is negligible. You only have to be concerned about wind and earthquakes. You can make it a millimeter thick at the base, but it has to zigzag or meander over a wide path.
 
EDIT TO ADD: An aerogel of CNTs and buckyballs could, conceivably be formed into a 350-meter wall thick enough and strong enough to stand against wind and earthquakes. It could have a thin skin of opaque material, perhaps graphene. It would be strong enough to keep out King Kong, but not hypersonic missiles.
For hurricane force winds, the base of a straight wall might have to be 10 meters thick. If it zigzags or meanders, it could be much thinner. It would, of course, have to be anchored to something heavy enough to withstand the force of the wind without being lifted into the air.
 
« Last Edit: 15/08/2013 07:02:08 by Phractality »
 

Offline Pmb

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Re: How can a 350 meter wall support itself?
« Reply #4 on: 15/08/2013 07:00:21 »
Quote from: Phractality
Strength is measured in units of pressure. How much pressure is needed to crush it? The pressure at a given height is equal to the weight of what's above that height divided by the cross section area. Each layer must support the weight of everything above it, so the bottom must be thickest.
What is most important in this case is the materials ability to withstand shear forces. Most materials will simply compress when weight is piled on top of it. What this has to withstand is the fact that the weight will cause the material to buckle under the stress. E.g. you can have a mountain of sand a mile high but not wall of sand that high since sand cannot support any shear stress. Another example is water. You can compress it all you want but it can't withstand any shear stress since it's a liquid. So the important thing is shear stress.
« Last Edit: 15/08/2013 07:01:58 by Pmb »
 

Offline Voxx

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Re: How can a 350 meter wall support itself?
« Reply #5 on: 16/08/2013 20:39:58 »
Aerogel, honeycomb structure, and rigidity are very good ideas guys.

However, I do need this 350 meter wall to be somewhat thick, I was thinking along the lines of 20 meters maximum and maybe 10 minimum.

I know this is pseudoscience, but humor me.  I have beings called Espers in my book (ESP, working WITH the laws of physics, not breaking them through mental calculations and using in-between universal energies as a catalyst for energy transfer).

If some of the more POWERFUL Espers have the ability to cause things along these abilities http://powerlisting.wikia.com/wiki/Earth_Manipulation or http://powerlisting.wikia.com/wiki/Electromagnetism_Manipulation.

Would they be able to create Carbon Nanotube material enough for the wall.  It could be all a singular mass or it could also be multiple honeycomb shaped sections placed together to form it.

How strong of an impact could it take and what would dismember it?  Would it need to be lined internally with a foundation of some heavier material to keep it grounded and how far would it need to be placed into the ground to add a solid foundation?  Would it survive hurricane conditions?
 

Offline CliffordK

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Re: How can a 350 meter wall support itself?
« Reply #6 on: 17/08/2013 10:47:16 »
Walled fortresses have largely become obsolete for the modern military. 

It takes quite a fortification to stand up to the pounding of an 80cm cannon.  Or a 44 ton explosion with conventional explosives, or a 50 megaton nuclear explosion.  And an airplane or helicopter can simply fly over a wall.  Thus, once the technology exists to make such a wall, it would already be obsolete.

Still, there are benefits of walls and fences to keep civilians in check.

The idea of a zig-zag, or perhaps a simple undulating sine wave was good for added strength.

I would build the wall out of conventional materials such as reinforced concrete and steel.  Stainless might be nice, but make a several inch, or perhaps even a foot thick mild steel facing, and it will last a good long time.  A couple hundred meters in height is well within the scope of traditional engineering, there is no need for exotic carbon nanotubes. 

The interior could either be designed to be hollow, and perhaps occupied by people, at least on one side of the wall, or it could be filled solid. 

I'm not sure of the dimensions.  For comparison, the World Trade Center was about 208 ft x 208 ft x 1368 ft, or 63m x 417m.
The Grand Coulee dam is about 550 feet (167.6 meters) tall, 450-500 feet thick at its base and 30 feet thick at the top.  It was excavated down to bedrock.

The World Trade Center was designed to take the impact of a jumbo jet, and it would have held up to the impact of a Boeing 747, if it wasn't for the fire.

Anyway, I would probably make your wall somewhat pyramid shaped, thin on top, thick on the bottom.  If you are expecting people to drive trucks into it, make it quite strong at the bottom, but not so much as one goes up the structure.  Excavate the foundations to bedrock, and thus the foundations wouldn't have to be too special.

« Last Edit: 17/08/2013 13:16:18 by CliffordK »
 

Offline alancalverd

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Re: How can a 350 meter wall support itself?
« Reply #7 on: 17/08/2013 15:14:32 »
Building a 350 m wall is no big deal. There are plenty of conventional buildings higher than that: you use a steel frame and any cladding that will withstand the windage at height. Earthquake proofing is largely a matter of tuning a flexible foundation to the natural frequency of the building - again conventional if somewhat new technology, but very much off-the-shelf. Despite being clad with glass, most ordinary skyscrapers generally survive hurricanes.

If you want it to withstand an impact, fill it with reinforced concrete. Make it as wide as you need to withstand the anticipated impact. You might do well to make the concrete into a 3 dimensional honeycomb filled with soft material like sand, so point impacts are absorbed locally and not transmitted along the rebars.

A 10 megaton nuke will create a crater about 20 m deep in soft earth, so you can assume that any resilient structure more than about 50 m thick will survive a single nuclear attack (the blast effect increases only with the square root of the explosive power, so there is little military value in anything with a yield greater than 10 MT - multiple dispersed hits are more effective.

The question nevertheless arises as to why you would want to build such a wall. Imagine a city surrounded by an impervious barrier only 10 m high. If a besieging army just blocked the drains, it would flood and become uninhabitable in a few years. Now there's a plot for you!


 
 

Offline Voxx

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Re: How can a 350 meter wall support itself?
« Reply #8 on: 17/08/2013 20:28:03 »
Alright.  As for the purpose of the wall, this city the wall is around is a totalitarian environment.  It isn't so much as to keep people out as keep people in and these people have ESP like abilities.

So that in mind, there is also several different segments to the city, splitting it into different areas.  Such as a northern side, docks, center, ect.  The sewage is patrolled (just to isolate that leak).  Note that his city has stood for two hundred and fifty years and the walls have only become more advanced to keep these powers in.

That being said, I think the nano tubing is an interesting idea.  I don't know exactly how strong it is or how much it weighs, but it seems like a promising structural foundation, being extremely strong.  I would still like to know what kind of element would completely destroy it, such as vibrations, chemicals or anything else (just to know its weakness).

It'll of course need to be made of different materials and have currents running through certain layers for certain ability users, but I'm looking for an extremely durable foundation that can stand to these different powers.  I like the stainless steel and mild tempered steel paneling ideas, but I'm looking for something that's the last measure defense.

Thickness can vary and I do like the honeycomb and rigid design ideas.  Thank you for your continued help!
 

lean bean

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Re: How can a 350 meter wall support itself?
« Reply #9 on: 18/08/2013 12:19:49 »
Must it be a wall?
Wouldn't a great circular tax office surrounding the city suffice?
 

Offline alancalverd

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Re: How can a 350 meter wall support itself?
« Reply #10 on: 18/08/2013 12:33:34 »
ESP won't protect you from an electric fence and razor wire, so keeping people in isn't a problem - pop along to Auschwitz to see how it is done in a totalitarian society.

That said, there was a particularly fine escape from the Soviet Bloc some years ago by a bloke who worked in an umbrella factory. He stole enough fabric to make a black hot-air balloon and just sailed over the fence on a moonless night, powered by a stripped-down gas stove. I've flown in very simple balloons to well over 1000m, so a wall ain't the answer either.   
« Last Edit: 18/08/2013 12:41:18 by alancalverd »
 

Offline Bored chemist

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Re: How can a 350 meter wall support itself?
« Reply #11 on: 18/08/2013 13:14:40 »
There's some data here for concrete
http://www.engineeringtoolbox.com/concrete-properties-d_1223.html
Density 2300 kg/m^3
Compressive strength 30MPa
At the bottom of a column of concrete 350m high the pressure is rho g h
About 8MPa

In terms of simple strength, concrete would do the job.
You could simply pile up concrete blocks until you got to 350 metres.
Of course, it would blow over with the first breath of wind, but guy ropes could solve that problem.
It would probably also buckle when the wind blew so you might need more guy ropes or- much more sensibly, you could build it thicker at the bottom than the top.

Given time and the inclination, the Romans could have done it.
The Egyptians probably could too but they didn't have concrete. They used rock and got half way there.
http://en.wikipedia.org/wiki/Great_Pyramid_of_Giza

Granite gives a higher strength at roughly the same density so you can get higher still.
And making the base thicker (which you need to do for stability) means that the compressive strength is even less of an issue.

No need for carbon nano-tubes or other high tech.
You can use a pile of rocks.
 

Offline yor_on

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Re: How can a 350 meter wall support itself?
« Reply #12 on: 18/08/2013 17:13:31 »
As you have the possibility to manipulate microscopically :)
Make it a diamond wall. let diamonds be nothing of worth, as they are possible to create with little cost in that thought up reality. Alternatively making this city as place of envy and power to all hearing about it, as it is extremely cost-some to manipulate carbon into diamond energy wise.

Although it would destroy whatever diamond market existing I guess :)
 

Offline Voxx

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Re: How can a 350 meter wall support itself?
« Reply #13 on: 18/08/2013 17:25:05 »
I guess I'm not being very clear upon the forces being contained.  Hmm, alright.  How about this.

In my version of ESP, we're not talking someone who can just telekinetically grab a rubber ball and throw it.  I'm talking about beings who can manipulate gravity to the point of light bending and directing kinetic energy (bit extreme examples, but I'm trying to put it in higher perspective).

You also have people of these abilities guarding the wall on top and patrolling in the streets and sewers.  Just getting a balloon and flying out isn't really an option when you have people who can see in inferred and electro-reception.

Note that these powerful Espers are the ones keeping these prisoner Espers in.  The wall is more of a determination factor to the normal Espers, like an electric fence for inmates.  Just like any wall, if someone really wants to try and get in a bank (and they have half a brain) they can figure out a way.  It's just there for that 99% of people who don't want to deal with the possible consequences.

An interesting thought Yor_on and I'd be willing to do it, but there is a need for some kind of gem market and as it's possible, I'm trying to think of different substance (combination of substances for redundancy against multiple abilities).
 

Offline yor_on

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Re: How can a 350 meter wall support itself?
« Reply #14 on: 18/08/2013 18:50:55 »
Maybe you could make it into some sort of semi crystal. Assume that diamonds, although possible, takes too much out of someone to create, except for a group of highly trained and motivated individuals, acting together getting some 'synergistic effect'. Then we just have to find a material that is stable, coming from carbon, and compressed, preferably also exotic in some manner, like maybe screening the city, etc (not found on the planet normally:) You might also let it act as a force multiplier when attuned to its frequencies, or frequency. And you may find that 'field' able to suppress peoples abilities, alternatively heighten them as long as they stay inside that city. Then you could have a natural reason why most people might accept a (benevolent) dictator ship. Although? I would revolt :)
 

Offline Bored chemist

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Re: How can a 350 meter wall support itself?
« Reply #15 on: 18/08/2013 19:41:25 »
Borrow some transparent aluminium form the makers of Star Trek.
Seriously, concrete would do but if you want something else to affect the plot line then make something up.
 

Offline dlorde

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Re: How can a 350 meter wall support itself?
« Reply #16 on: 18/08/2013 21:17:32 »
Diamond is hard, but vulnerable to heat, starting to break down above 700 C.
 

Offline Voxx

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Re: How can a 350 meter wall support itself?
« Reply #17 on: 19/08/2013 04:38:35 »
If I just wanted to make up some amazing brand new material of wonder then I wouldn't have asked a science form xD

Concrete is a good generic way to make a wall, but at the same time is easily deteriorated.  I'm looking for something a little more durable to freedom fighters escape attempts.

Is there a reason Carbon Nano-tubes are inefficient?

Also, what color would you expect carbon nano-tubes to be?

Another thing that I'm still unclear on is its strength.  People have commented on the destructive capability of certain weapons, but have yet to give me an estimation on carbon nano-tubes strengths/weaknesses (at least as much as I can remember).

Crystal would be an interesting addition, but can be shattered at different frequencies.

There are stones that suppress Esper abilities, these stones were exposed to in-between space during the experiment.  However, the guards also use ESP so that would be counter productive.   
 

Offline CliffordK

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Re: How can a 350 meter wall support itself?
« Reply #18 on: 19/08/2013 06:16:25 »
Crystals?  Transparent Aluminum?  Ceramics?

Aluminum Oxide can be made into a transparent form of synthetic sapphire that has excellent strength and transparency qualities.  Likewise, zirconium dioxide also makes excellent crystals.

Thermal expansion may well be an issue for a monolithic wall, however, perhaps that would be another reason for a sinusoidal shape, which might also give it better earthquake tolerance, especially over long distances.

Make the monolith crystal big and thick enough, and you'd have troubles shattering it with resonance.  There would have to be a way to break up resonance.  Perhaps not doing a pure sine wave form, but adding subtle variation in the height, thickness, shape and other features of the wall.
 

Offline Voxx

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Re: How can a 350 meter wall support itself?
« Reply #19 on: 19/08/2013 15:39:20 »
Wouldn't a carbon wall be the most durable and resilient?  I believe hearing somewhere that its melting point is near 3,500 degrees C. 
 

Offline Bored chemist

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Re: How can a 350 meter wall support itself?
« Reply #20 on: 19/08/2013 19:56:44 »
Wouldn't a carbon wall be the most durable and resilient?  I believe hearing somewhere that its melting point is near 3,500 degrees C. 
It would be durable until someone took a blowtorch to it.
 

Offline CliffordK

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Re: How can a 350 meter wall support itself?
« Reply #21 on: 19/08/2013 22:31:12 »
Does diamond burn very well?

Carbon Fiber is typically a resin composite, much like fiberglass.  Certainly fiberglass burns quite well, and many resin composites would also burn quite well.  A carbon fiber wall may be a good channel for lightening too.

I think the idea with carbon nanotubes is to weave a yarn with them, and perhaps make ropes and cables without added resin.  However, currently the individual fiber lengths are short, and woven cables with short nanotubes tend to be relatively weak.
 

Offline dlorde

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Re: How can a 350 meter wall support itself?
« Reply #22 on: 20/08/2013 00:23:59 »
Does diamond burn very well?
Yes, well enough (I've been told) that jewellers need to take precautions when using certain high temp solders when mounting them.
 

lean bean

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Re: How can a 350 meter wall support itself?
« Reply #23 on: 20/08/2013 19:11:44 »
Liquid oxygen isn't a diamond's best friend.
 

Offline Bored chemist

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Re: How can a 350 meter wall support itself?
« Reply #24 on: 20/08/2013 22:14:37 »
Does diamond burn very well?

Carbon Fiber is typically a resin composite, much like fiberglass.  Certainly fiberglass burns quite well, and many resin composites would also burn quite well.  A carbon fiber wall may be a good channel for lightening too.

I think the idea with carbon nanotubes is to weave a yarn with them, and perhaps make ropes and cables without added resin.  However, currently the individual fiber lengths are short, and woven cables with short nanotubes tend to be relatively weak.
I had forgotten about lightning.
No need to wait for someone with a blowtorch. It will catch fire in the first storm.

On the other hand "Concrete is a good generic way to make a wall, but at the same time is easily deteriorated. " In the very real sense that we still have concrete which the Romans left behind.
Obviously, nothing is indestructible, but it's silly to forget that a damned thick concrete wall is cheap and it's durable simply because moving a heavy thing takes a lot of energy.
 

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Re: How can a 350 meter wall support itself?
« Reply #24 on: 20/08/2013 22:14:37 »

 

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