Stability of Water and Sand Mixture

[purest123]

Hi,
I'm doing a project on the strongest mixture of sand and water(or other
granular materials) and I can't think of a good way to test it. I found
a scientific paper written by Arshad Kudrolli (Maximum Angle of Stability of a Wet Granular Pile) and what they did was they used plexiglass and filled
it with glass beads and water. Then they took a video with a high speed
camera, but I'm an amateur and don't have access to those equipments,
any ideas?

Any help would be appreciated

Marshall

[deleted-2574]

Hi Marshall!

Yikes, there has to be a better way than a high speed camera!

Plugging in "how to test a water and sand mixture" to answers.com, you get back several responses including:

http://www.selah.k12.wa.us/JHS/Brown/CA ... iProj.html
http://www.k12science.org/curriculum/wa ... ties.shtml
http://www.stevespanglerscience.com/experiment/00000088 - warning borders on being commercial

The sites above were generated by submitting "How to test a water and sand mixture" to answers.com. Two notes in using answers.com:

1. Generally, the "Sponsored Links" are commercials. So, it's best to skip them and use only the links in "Web Search." There are several sites in the Web Search to skip, however, since they're just trying to sell something.

2. With answers.com, you may need to tweak your wording for best results.

[purest123]

I always thought that Google is the best... oh well

thanks a lot!!!

[deleted-2574]

Hi marshall!

answers.com is a front-end to google for web searchs. I can't say in detail how they differ, but answers appears to have made both cosmetic and reordering changes.

[deleted-2131]

purest123,

If I understand your problem correctly, you are trying to determine the ratio of sand to water that results in the pile of sand with steepest sides.

Scientists call the steepness of the side of a pile of sand/water mixture (or any other granular substance) the angle of repose. Try searching for more information on the angle of repose of sand.

Adding water to the sand will definately affect the sand's angle of repose, though I will leave it to you to determine what that effect will be.

I would suggest setting up an experiment in which you have different sand water mixtures (e.g. 2:1, 1:1, 4:1, etc) and then poured a fixed amount of the sand mixture from a fixed height. You could then measure the angle of repose of the sand/water mixture using a variety of methods. Be sure to also use plain sand and plain water as controls.

If you are now totally confused, please let me know. I would be more than happy to work with you to design a super science project. This is a great topic for a project and has many real-world applications!

[purest123]

If I understand your problem correctly, you are trying to determine the ratio of sand to water that results in the pile of sand with steepest sides.

That is exactly what I want to do!

I am going to turn in my research tomorrow so I can get the project started.

I would suggest setting up an experiment in which you have different sand water mixtures (e.g. 2:1, 1:1, 4:1, etc)

that is also what i want to do too. . But as i said, i just can't use a high speed camera to test it(although that would be really cool). I thought of building a rig to see at what angle a sand mixture tower will collapse or build another rig that drops marbles on a sand mixture tower...took me
hours to think up... science fair is going to be tiring

Marshall

[deleted-2131]

Yes, I will agree with you that science fair can be tiring and involves some serious hard work, but it is all worth it ... your work really pays off in the end.

I like the ideas you have put forth. You might also want to consider just measuring the angle at which the pile settles. For example: Pour 2 kilos of a mixture of 1 part sand, two parts water from a height of 0.5 meters. Let the pile settle for five minutes. Then take a large piece of paper and put it behind the pile. Shine a light source at the pile and then measure the angle between the shadow of the pile and the edge of the paper. This method will provide you decent results as long as the light source stays in the same place relative to the pile.

If this doesn't make sense, let me know and I will see if I can explain it better.

Good luck!

[deleted-71447]

Sounds like a great project, and well underway. I have a couple of additional thoughts to consider in designing your experiments:

You will be somewhat limited in the ratio of sand to water that you can use. The typical porosity of sandy sediments is something around 0.3, so you may not be able to use much more than 1 parts water to 3 parts sand (by volume) without having a bunch of water that just sloshes around on the sand and does not enter the pore space.

Also, if you are working with sand that is saturated or almost saturated, the water will drain very rapidly. Within seconds, your water content will vary between the top and the bottom of the pile.

One way to overcome these problems would be to work with very low water contents. If the water content is low enough, then the hydraulic conductivity of the sediments will be low enough that you can maintain a uniform water content throughout your pile of sand. You could oven dry the sand, then add small amounts of water to vary the water content. If you wanted to be thorough, you could, after each trial of the experiement, take samples from the top and bottom of the pile, weight them, oven dry them, then weigh them again to see if you have any variation in water content from top to bottom.

[purest123]

Also, if you are working with sand that is saturated or almost saturated, the water will drain very rapidly. Within seconds, your water content will vary between the top and the bottom of the pile.

Is there anyway I can extend the time before the water content gets pulled to the bottom of the pile? I make a lot of mistakes when I rush...ah memories

Let the pile settle for five minutes. Then take a large piece of paper and put it behind the pile. Shine a light source at the pile and then measure the angle between the shadow of the pile and the edge of the paper. This method will provide you decent results as long as the light source stays in the same place relative to the pile.

Wouldn't it be a problem with larger water contents since they tend to group together ie. sandcastles?

[deleted-2131]

The only way that I am aware of to lengthen the time until the water drains is to decrease the amount of water in the sand. (e.g. a mixture of 1 part water to 10 parts sand will drain faster than a mixture of 1 part water to 4 parts sand).

As to your second query: This isn't a problem. What you have just mentioned is part of your experiment. You have made an observation. As you go through the process of completing your project you will figure out what your observation means to your project.

[purest123]

The only way that I am aware of to lengthen the time until the water drains is to decrease the amount of water in the sand. (e.g. a mixture of 1 part water to 10 parts sand will drain faster than a mixture of 1 part water to 4 parts sand).

so that means i'll have to live with it.

Thank u sooo much for your help!!!!!!!!!!!!!

marshall

[deleted-71447]

so that means i'll have to live with it.

It should be pretty easy to work around. For your current experimental design, I would recommend that you start with water:sand ratios (by volume) ranging from 1:50 to 1:10. Mix well! You can use more water if you use finer grained sand.

Here are some terms that may be helpful for you:

'Pore space' is the volume in a sediment that is not filled by solid grains.

'Water content' or 'moisture content' is a number that represents the volume of water per volume of sediment. At the lower limit, it is 0. At the upper limit, it is equal to the pore space of the sediment (usually < 0.4, but depends on the particular sediment). For example, a mixture of 1 part water to 10 parts sand, by volume, has a moisture content of 0.1.

A soil or sediment is said to be 'saturated' when all the pore space is filled with water and 'unsaturated' when some of the pore space contains air.

'Hydraulic conductivity' is the ability of a porous substances (like sand) to transmit water. For lower water content, hydraulic conductivity is also lower. For sands, this effect is dramatic. For example, it would not be unusual for a sand to transmit water 10,000 times more slowly (hydraulic conductivity reduced by a factor of 10,000) when the moisture content drops from 0.3 to 0.1.

[purest123]

So to calculate water contents you take the ratio of water and divide by the ratio of sand.
So Hydraulic conductivity is responsible for the fast draining of sand.

[deleted-71447]

Yes, you could express it mathematically as:

water content = volume of water / volume of sand & water mixture

If there is less water than pore space in the sand (as there should be for your experiment) then the water will occupy pore space, and the volume of sand will be equal to the volume of the water and sand mixture. In that case, the above equation becomes:

water content = volume of water / volume of sand

As for hydraulic conductivity, you can think of it as the width of a bottleneck. A bottle with a tiny opening (low conductivity) will empty slowly, while a bottle with a large opening (high conductivity) will empty very quickly. There are all sorts of equations that are more precise, if you are interested.

[purest123]

Okay.
Thanks for all of your help!!!

Now I have an idea of where to go.

[deleted-2131]

You are most very welcome. Thank you for being such a motivated student scientist!

[purest123]

Sorry for the additional post, I can't edit my original one

I have one last question - what is the best way to mix sand and
water together, with a mixer, spoon, or just hand...or other stuff i don't know
about

Thanks in advance

[deleted-71447]

Purest - Thanks for staying involved and keeping us updated on your progress. It's fun to hear about the experiment as it unfolds.

Either a spoon or an electric mixer should be fine as long as you mix until the water is evenly spread through the sand. If you can use small amounts of sand, then a spoon will probably be adequate. If you need to use a large amount of sand, then an electric mixer or power-drill mixer attachment may be necessary. I would do a trial run with a small amount of sand mixed with a spoon, for the sake of ease and simplicity. If you find that the small quantities aren't sufficient, then you can revise the procedure to use larger amounts and different mixing techniques.

[purest123]

Thanks for all your help!

sry for the late reply, I had a lot of homework and had to do volunteer
hours....

[deleted-71447]

No problem. I hope the experiment goes well. Keep us posted!

[deleted-2131]

Good luck! If you need anything, just let us know.