I have a strange question I hope someone here may be able to help with.
Scenario: imagine washing and sifting several tons of sand. This is to be used on a soundstage to create a desert scene. The sand has been washed and sifted so that if it gets kicked up, it won't form dust clouds. The sand particles are of a size that they will still hold a boot print or a tyre mark.
Question: will the act of transporting the sand, and dumping it in situ, cause sufficient erosion of the sand so that it might still produce some dust when kicked around on the sound stage? Would driving a vehicle on the sand be expected to produce clouds of dust that are visible in the atmosphere, rather than falling straight back down to earth?
In your answer could you also let me know your level of Geology expertise, and whether you consider this a basic question that a layman such as myself should automatically know the answer to?
Once I have some answers I shall let you know the reason for my request, but I don't want to prejudice your answers.
Depends on what you actually want realism wise. Desert sand (dry) won't hold a boot print or type track perfectly and will kick up a lot of dust (more so with large vehicles). Many deserts have a surface crust and boots may make no impression.
Spreading sand won't alter its properties much. Moisture content will.
If you want tyre tracks and boot prints and no dust I'd use sharp sand and keep it slightly damp - you could always cover the surface with a thin layer of dry playsand or sliversand for a better surface effect.
Expertise: Professional geologist/geophysicist with field experience in the Atacama desert.
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Geologists like a nappe between thrusts
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Fri, 09/28/2007 - 22:49
Jon Rank: Corundum Joined: 18/12/2006 Points: 3524
As Hypocentre says, wet sand holds the best boot print, dry sand will hold an indentation (at best). Sand refers to a grain size. I assume when you say sand, you mean sand-sized grains of quartz. You can have very coarse sand (~1.5m diameter grains) all the way down to very fine sands (~0.075m diameter grains). I would expect perfectly dry, very fine sand to be kicked up into the atmosphere and produce a bit of dust, depending on the speed of the vehicle (I think a wind speed of 20km/h will lift a 0.1mm grain into suspension). But then coarse sand would not be so easily put into suspension; hence no dust cloud.
Moving and sifting sand is unlikely to produce any finer grains (unless you really go at it and whack it with hammers or something!). However, I think it highly unlikely you could wash and sieve several tonnes of sand and get it all the same grain size...
to save you days and tons of work i would advise going to the next sand pit and ask how much it would cost to buy some cubic meters of sand of a special grain size.
to cleanly sort them you might likely need a flotation device and sedimentation basin (i am not sure on the correct english terms for these).
Thanks for the advice, but this is purely an intellectual exercise. Is it possible to come to any definite conclusions about whether dust clouds would be seen in the scenario given? Yes, no, impossible to know without experimentation, or some other answer?
transportation and dumping the sand will not be enough to cause dust creation unless you had a very dirty an dusty transport container.
driving a vehicle thru it will not creat dust either (unless you repeat the process insanely often to grind down the sand grains)
also, if the sand has been washed and sifted that it won't form dustclouds it is also unlikely that it will hold a footprint or tiremark. you will only see an impression but with no details. the shape of the grains might influence this though. i can imagine having perfectly rounded grains compared to very angular ones will make a difference. dont know how big this will be though. however, for building sand castles sand that is very angular is used bc it holds better together. usually (as a vague rule of thumb) river sand is often more angular than beach sand.
the creation of dust requires a certain grain size that is to my knowledge (i am not a sand nor dust expert) below the grain size of what people like you and me would consider sand. you would likely require a minimum amount of silt (unsure) or clay particles that are sufficiently small to be able to be suspended in the air for some time. also these particles must be really dry. if there is some moisture or even water there will be no dust, only mud or dirt.
you could test this by dropping different samples into a column of water. sand and silt to some degree will sediment pretty quickly clay particles on the other hand will need very long and are also light enough to be uplifted by small turbulences in the water. this isnt a good scientific explaination i think but image your water is now the air.
i am certain you could create an experimental setting with different grain sizes and controlled sample and air humidity(should affect dust creation, too).
Rank: Fluorite
Joined: 19/01/2006
Points: 390
Depends on what you actually want realism wise. Desert sand (dry) won't hold a boot print or type track perfectly and will kick up a lot of dust (more so with large vehicles). Many deserts have a surface crust and boots may make no impression.
Spreading sand won't alter its properties much. Moisture content will.
If you want tyre tracks and boot prints and no dust I'd use sharp sand and keep it slightly damp - you could always cover the surface with a thin layer of dry playsand or sliversand for a better surface effect.
Expertise: Professional geologist/geophysicist with field experience in the Atacama desert.
Geologists like a nappe between thrusts
Rank: Corundum
Joined: 18/12/2006
Points: 3524
You could always experiment on a beach!
As Hypocentre says, wet sand holds the best boot print, dry sand will hold an indentation (at best). Sand refers to a grain size. I assume when you say sand, you mean sand-sized grains of quartz. You can have very coarse sand (~1.5m diameter grains) all the way down to very fine sands (~0.075m diameter grains). I would expect perfectly dry, very fine sand to be kicked up into the atmosphere and produce a bit of dust, depending on the speed of the vehicle (I think a wind speed of 20km/h will lift a 0.1mm grain into suspension). But then coarse sand would not be so easily put into suspension; hence no dust cloud.
Moving and sifting sand is unlikely to produce any finer grains (unless you really go at it and whack it with hammers or something!). However, I think it highly unlikely you could wash and sieve several tonnes of sand and get it all the same grain size...
Geologists are gneiss!!
Rank: Gypsum
Joined: 12/07/2007
Points: 54
to save you days and tons of work i would advise going to the next sand pit and ask how much it would cost to buy some cubic meters of sand of a special grain size.
to cleanly sort them you might likely need a flotation device and sedimentation basin (i am not sure on the correct english terms for these).
Rank: Talc
Joined: 27/09/2007
Points: 2
Thanks for the advice, but this is purely an intellectual exercise. Is it possible to come to any definite conclusions about whether dust clouds would be seen in the scenario given? Yes, no, impossible to know without experimentation, or some other answer?
Cheers!
Rank: Gypsum
Joined: 12/07/2007
Points: 54
transportation and dumping the sand will not be enough to cause dust creation unless you had a very dirty an dusty transport container.
driving a vehicle thru it will not creat dust either (unless you repeat the process insanely often to grind down the sand grains)
also, if the sand has been washed and sifted that it won't form dustclouds it is also unlikely that it will hold a footprint or tiremark. you will only see an impression but with no details. the shape of the grains might influence this though. i can imagine having perfectly rounded grains compared to very angular ones will make a difference. dont know how big this will be though. however, for building sand castles sand that is very angular is used bc it holds better together. usually (as a vague rule of thumb) river sand is often more angular than beach sand.
the creation of dust requires a certain grain size that is to my knowledge (i am not a sand nor dust expert) below the grain size of what people like you and me would consider sand. you would likely require a minimum amount of silt (unsure) or clay particles that are sufficiently small to be able to be suspended in the air for some time. also these particles must be really dry. if there is some moisture or even water there will be no dust, only mud or dirt.
you could test this by dropping different samples into a column of water. sand and silt to some degree will sediment pretty quickly clay particles on the other hand will need very long and are also light enough to be uplifted by small turbulences in the water. this isnt a good scientific explaination i think but image your water is now the air.
i am certain you could create an experimental setting with different grain sizes and controlled sample and air humidity(should affect dust creation, too).