Quicksand facts

[EHocking]

Originally Posted by LibraryLady

Don't worry, Tarzan will always rescue you.

Or an elephant (even if your mouse drives a Porsche).
NSFW.

[I Ratant]

Originally Posted by quarky

Domini Domini.

I will say 5 Hail Mary's for your sins.

.
I had been keeping count, but dropped the effort, on tabulating one very major mortal sin... stopped somewhere about 4700, if memory serves.
Still choking that thing anyway.

[RenaissanceBiker]

I can't believe I almost missed a quicksand thread.

Originally Posted by Soapy Sam

If sand is denser than water, then it can't be suspended in water, unless something is keeping it suspended.

Correct. That something is the pore pressure of water. If there is a sufficient upward gradiant of water pressure then the sand-water mixture can liquify. The shockwave of an earthquake can also cause quicksand to temporarily form.

I made a quicksand tank in engineering school as a demonstration of soil mechanics for visiting high school students. It involved a 55-gallon drum full of sand and water with a large hose at the bottom connected to a 5-gallon bucket of water. The bucket was attached to a rope and pulley system so that it could be rasied quickly. I would stand on the top of the sand and signal another man to pull up the bucket. This would cause a temporary upward pressure and liquify the sand-water mix. I would sink to my waist. As soon as the pressure was normal the sand would settle out and I would be stuck. To get out, the other man had to lower the bucket and allow the water to drain back into it, then raise it quickly again. I only had a few seconds to pull myself out but it was easy to do.

Originally Posted by Soapy Sam

Most "quicksand" is actually mud. Clay.

Eh, no. Mud is mud. Clay is clay. Sand is sand. They are defined by their particle size. The greater porosity of sand and even gravel allows the water pressure wave to travel through it rapidly and cause it to liquify or become "quick." I'm not downplaying the danger of mud, but it's not the same physical phenomena. Mud can exist as a liquid without the pressure gradiant because of its lower porosity. I can see why people confuse the two but they are not the same thing.

[Soapy Sam]

Originally Posted by RenaissanceBiker

I can't believe I almost missed a quicksand thread.

Correct. That something is the pore pressure of water. If there is a sufficient upward gradiant of water pressure then the sand-water mixture can liquify. The shockwave of an earthquake can also cause quicksand to temporarily form.

I made a quicksand tank in engineering school as a demonstration of soil mechanics for visiting high school students. It involved a 55-gallon drum full of sand and water with a large hose at the bottom connected to a 5-gallon bucket of water. The bucket was attached to a rope and pulley system so that it could be rasied quickly. I would stand on the top of the sand and signal another man to pull up the bucket. This would cause a temporary upward pressure and liquify the sand-water mix. I would sink to my waist. As soon as the pressure was normal the sand would settle out and I would be stuck. To get out, the other man had to lower the bucket and allow the water to drain back into it, then raise it quickly again. I only had a few seconds to pull myself out but it was easy to do.


Eh, no. Mud is mud. Clay is clay. Sand is sand. They are defined by their particle size. The greater porosity of sand and even gravel allows the water pressure wave to travel through it rapidly and cause it to liquify or become "quick." I'm not downplaying the danger of mud, but it's not the same physical phenomena. Mud can exist as a liquid without the pressure gradiant because of its lower porosity. I can see why people confuse the two but they are not the same thing.

I have no argument with what you say here, but the term "quicksand" as popularly used (especially in movies) rarely refers to "true" quicksand as you describe it. Far more often it seems to involve mires, bogs, tar"sands" etc. (ie the definitive character is something soil-like that you sink in.-In Britain, it's apt to be a slurry of peat with a thin crust of heather etc on top- go through it on a dark night , come up six feet away and you may well never find the hole you fell through. Fortunately, most such are pretty shallow.)

Was your barrel quicksand grain supported at all or 100% fluid ? (Hard question to answer, I know). The only true quicksand I've encountered is in the Solway estuary between England and Scotland, but even that, when dumped in a glass jar and stirred, contained up to 12% clay, plus a surprising (to me) amount of gravel grade shell fragments (mollusc, not military).
ETA- The army use parts of the area as a live fire ground, so military shells are more likely than you might expect)

[alfaniner]

At the risk of spoiling the 12 hours of the Super-Extended-Enhanced-Special-Edition of The Lord of the Rings series:

One can't sink in lava, either.

[Soapy Sam]

You probably can if it's degassing violently. (It's frothy, man!)
Especially with a magic ring on your finger.

[pipelineaudio]

I lived along the Hassayampa river, literally "the river that lies (both meanings) underground". Day after day after day of following my same tracks was no gurantee against my jeep nearly being lost to quicksand one cold morning. I've lost slippers in it, but never felt like I was being pulled down. My jeep on the other hand was sinking like a rock! When I finally got it out, a GOOD winch no longer seemed like a frivolous investment

[ZirconBlue]

Originally Posted by alfaniner

At the risk of spoiling the 12 hours of the Super-Extended-Enhanced-Special-Edition of The Lord of the Rings series:

One can't sink in lava, either.

Really?

[RenaissanceBiker]

Originally Posted by Soapy Sam

I have no argument with what you say here, but the term "quicksand" as popularly used (especially in movies) rarely refers to "true" quicksand as you describe it. Far more often it seems to involve mires, bogs, tar"sands" etc. (ie the definitive character is something soil-like that you sink in.-In Britain, it's apt to be a slurry of peat with a thin crust of heather etc on top- go through it on a dark night , come up six feet away and you may well never find the hole you fell through. Fortunately, most such are pretty shallow.)

I'm an engineer so I get hung up on strict definitions sometimes.

Originally Posted by Soapy Sam

Was your barrel quicksand grain supported at all or 100% fluid ? (Hard question to answer, I know). The only true quicksand I've encountered is in the Solway estuary between England and Scotland, but even that, when dumped in a glass jar and stirred, contained up to 12% clay, plus a surprising (to me) amount of gravel grade shell fragments (mollusc, not military).
ETA- The army use parts of the area as a live fire ground, so military shells are more likely than you might expect)

We used playground sand so it was pretty clean. When the water in the pores was not actually moving upwards it was like standing on the beach. When the water was moving upwards it was able to lift the sand particles and cause the whole mixture to become a liquid. Imagine a particle of sand in a glass where water is right at the surface but not moving. Gravity is pulling it down and bouyancy is pushing it up. It doesn't move because it is resting on the sand particles below it. If pressure from below starts moving the water upwards, the sand particle will also experience an upwards drag force. When the drag force plus the bouyant force equals the force of gravity, the sand particle will be on the verge of movement. At that point, the sand-water mixture becomes "quick."

When you add particles of various sizes such as clay, silt, etc. the math becomes more complicated because the porosity changes and so does the drag force. The water is not able to move as easily through lower porosity.

[Soapy Sam]

Originally Posted by ZirconBlue

Really?

Most lava will be a lot denser than water - and most people float in that. Plus lava is generally cooling fast on the outside, forming pretty viscous skin. Not that any of this matters much, as you will be quite singed.

Lava does often contain a lot of dissolved gas and steam, which might drop the upper layer density enough to let you sink.

Not an experiment I'd want anyone to try.

[Soapy Sam]

Originally Posted by RenaissanceBiker

I'm an engineer so I get hung up on strict definitions sometimes.

Fair enough.

Quote:

We used playground sand so it was pretty clean. When the water in the pores was not actually moving upwards it was like standing on the beach. When the water was moving upwards it was able to lift the sand particles and cause the whole mixture to become a liquid. Imagine a particle of sand in a glass where water is right at the surface but not moving. Gravity is pulling it down and bouyancy is pushing it up. It doesn't move because it is resting on the sand particles below it. If pressure from below starts moving the water upwards, the sand particle will also experience an upwards drag force. When the drag force plus the bouyant force equals the force of gravity, the sand particle will be on the verge of movement. At that point, the sand-water mixture becomes "quick."

This is very like the scenario I mentioned where air is used as the carrier fluid to fluidise bulk powdered cement or barite, or grain in a silo , prior to blowing it through a transfer line.
In a natural context, if the water current is fast / powerful enough to reach surface, it would be apparent as bubbling. Of course someone might easily drive into that, especially in rain or the dark. As the minimum density is that of water and there is also an upward drag component, it would be hard to sink in this, though you might be easily turned on your face- especially if wearing a pack.
But it's easy to see how you could be trapped if the water movement decreases and you find yourself buried in a sandpile.

Quote:

When you add particles of various sizes such as clay, silt, etc. the math becomes more complicated because the porosity changes and so does the drag force. The water is not able to move as easily through lower porosity.

Tell me about it. I mix drilling mud for a living.

[quarky]

The one place I found where super-saturated sand felt threatening was in a Florida spring, with up-welling water in a large sand basin. I think it changes the equation. In fact, there's an obscure Florida spring that gushes up with enough force to keep small chunks of old coral at the surface of the water. Very strange to behold.

[Skeptical Greg]

Originally Posted by I Ratant

.
The tragedies occur when Tommy falls into the quicksand and the time Lassie takes to run home for help is too long, and Tommy goes under...

As long as it's not Timmy, who cares about Tommy ?

[quarky]

Jeff precedes Timmy and Tommy.
Jeff was way less waspy than Timmy.
And Gramps was fairly crusty for tv.
They don't make curmudgeons like Gramps (or Amos McCoy, for that matter) anymore.

get off my lawn, btw.

[Soapy Sam]

Originally Posted by quarky

The one place I found where super-saturated sand felt threatening was in a Florida spring, with up-welling water in a large sand basin. I think it changes the equation. In fact, there's an obscure Florida spring that gushes up with enough force to keep small chunks of old coral at the surface of the water. Very strange to behold.

Sounds very like RB's barrel.

[I Ratant]

Originally Posted by quarky

Jeff precedes Timmy and Tommy.
Jeff was way less waspy than Timmy.
And Gramps was fairly crusty for tv.
They don't make curmudgeons like Gramps (or Amos McCoy, for that matter) anymore.

get off my lawn, btw.

.
Checked out the series on the Hatfields and McCoys?
Devil Anse Hatfield.... nasty mother!

[ben m]

Originally Posted by RenaissanceBiker

I made a quicksand tank in engineering school as a demonstration of soil mechanics for visiting high school students. It involved a 55-gallon drum full of sand and water with a large hose at the bottom connected to a 5-gallon bucket of water. The bucket was attached to a rope and pulley system so that it could be rasied quickly. I would stand on the top of the sand and signal another man to pull up the bucket. This would cause a temporary upward pressure and liquify the sand-water mix. I would sink to my waist. As soon as the pressure was normal the sand would settle out and I would be stuck. To get out, the other man had to lower the bucket and allow the water to drain back into it, then raise it quickly again. I only had a few seconds to pull myself out but it was easy to do.

I want to try this now.

[Soapy Sam]

You might find it easier / less messy to use air as the carrier fluid and a lighter material (rice? grain?) as the "sand" at least in the early stage. But I agree the wet and sandy version sounds more satisfying.