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In a recent discussion on the thixotropic effect of sustained long-period geoseismic activity beneath Mexico City I realised the solution to the problem of soil liquefaction experienced in areas of similarly risky soils.
One of the reasons these areas are so risky is the groundwater saturation of
sedimentary soils.
Humans love to pump groundwater to the surface, for growing crops, showering, washing cars, hosing sidewalks, etc.
The solution is simple: Recycle water runoff, adding cornstarch before pumping it back into the ground.
You still get the wobbly effect you know and love... until an earthquake hits and the renowned custard effect kicks in. Earthquake strikes, ground goes rock solid. :)
Mexico City EQ damage
http://www.ngdc.noa...document/647003.htm
[werdna, Oct 05 2004, last modified Oct 21 2004]
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have you *seen* the price of custard powder? |
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It's inflated. Cornstarch is an ingredient of industrial adhesives. It is turned out by the hundreds of thousands of tons, and is quite a cheap commodity. We could harness the subsidised maize crops from the US Midwest for this task. |
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OK, I believe you, thousands wouldn't but thats another story +1 |
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Maize to Mexico - that could be a new substitute for "Coals to Newcastle". |
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does this mean everything would bounce in Mexico city? |
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If you add borax to that water with
everything else you would have city
putty. + |
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A whole new breed of custard filled rodents could develop that lives off that soil. If you whack them with a regular trap they just turn rock solid, then slowly turn soft again and wiggle out. Would the Mexicans like that? |
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Wouldn't the pumping action and turbulence prohibit the easy flow of cornstarch/custard water back into the soil? Sounds like it would gum up the works. How about bombs, filled with dry cornstarch, that are deployed under the surface via deep drills-- when they explode they mix with the groundwater. Just enough to cause mixing without excessive surface vibrations, of course. Voila, instant subterranean city putty. |
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When the water is pumped back out it is separated from the cornstarch, by baking in the hot sun, and the cornstarch residue is used to thicken sauces and make you know what. |
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I guess it would be equally easy to pump concrete back into the ground, for the same effect. That would make the water inaccessible for a while, but it might be a solution that Mexico City could look at. |
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Concrete is full of nasty chemicals that are probably best left out of the groundwater. |
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Did some more research (link)-- most of the building damage in MC was observed in buildings whose fundamental periods were closely aligned with the underlying soil. There was some liquefaction but it was apparently highly localized. It seems that the soil was more like jello (too springy) than quicksand (liquefiable). |
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Mid-rise apartment buildings were especially vulnerable because their periods (say, 0.5 to 1.5 seconds) were similar to the soil's vibration period. If the vibration of a building is coupled with soil vibration then there is a resonance problem; the key is to pump enough cornstarch to make the vibration period of the soil short (i.e., stiff) enough so that serious resonance is not an issue. Like vibration isolation in fan housings to control noise. |
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With stiffer soil, short buildings would be more vulnerable to soil vibrations. With springier soil, taller buildings are more vulnerable. Cornstarch bombs could be deployed in a carefully mixed recipe locally under mid-rise buildings without affecting neighboring buildings. |
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Mud Custard. I'm sure some kid has thought of it. |
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[werdna], would that periodicity be fast enough to induce the dilatant effect of the cornstarch solution? |
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I haven't shaken cornstarch putty in 15 years so I can't recall how vigorously it needs to be shaken to stiffen. Controlling the proportions of water and cornstarch, I think, changes the vibration properties so there are probably some mix design tolerances. |
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Gotta research this in the kitchen with a bowl of corstarch putty and a stopwatch. There's probably similitude effects that could be important but let's just ignore them. NSF funding? |
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