Soil Density Calculations
Meghan Sindelar
Author
06/22/2016
Added
3580
Plays
Description
This recording captures the author working calculations to determine soil bulk density and soil particle density from collected data.
Searchable Transcript
Toggle between list and paragraph view.
- [00:00:01.504]Hello.
- [00:00:02.469]Dr. Meghan Sindelar here.
- [00:00:04.235]This video is an example calculation of doing
- [00:00:07.949]bulk density and particle density calculations
- [00:00:11.327]for the soil physical properties.
- [00:00:13.336]It is assumed that you are familiar with these concepts
- [00:00:16.258]and just want to see an example of worked problems.
- [00:00:21.008]Here are the formulas.
- [00:00:23.275]All density is a mass per volume.
- [00:00:28.408]So, you got the volume of this thing, weight it.
- [00:00:36.462]Okay, so bulk density is the mass of solids in soil
- [00:00:40.574]so air doesn't weigh much,
- [00:00:42.546]water is variable so we don't use that,
- [00:00:45.299]just mass of solids over the total or bulk volume of soil.
- [00:00:53.339]Particle density is still the mass of solids
- [00:00:56.846]but now we're only looking at the volume of solids
- [00:00:59.919]or volume of particles.
- [00:01:03.075]And so, particle density just tells us about
- [00:01:05.048]the properties of the given solids.
- [00:01:09.635]Like, how dense is this sand grain?
- [00:01:12.043]And so, volume of solids is often determined by
- [00:01:15.468]water displacement or really not determined at all.
- [00:01:21.015]Okay, here's an example of some data
- [00:01:22.919]you might collect in the field.
- [00:01:25.341]So, use a tin of known volume,
- [00:01:29.053]get some soil in it at field moisture, it's a certain weight,
- [00:01:33.534]goes in the oven at 105 degrees for 24 hours.
- [00:01:37.146]Now, we've got a lighter weight
- [00:01:38.436]because the water's been driven off.
- [00:01:40.667]Don't forget to subtract with the tin weight.
- [00:01:43.694]Here are the dimensions of our tin
- [00:01:45.674]so we can figure out the total volume of soil that we had.
- [00:01:51.826]And then, in some cases,
- [00:01:54.107]you might grind your dry soil sample,
- [00:01:58.753]place it in water to get a displacement
- [00:02:01.480]and that then is your volume of solids.
- [00:02:05.268]So, if it displaces 57 milliliters of water,
- [00:02:08.811]a milliliter is equal to a cubic centimeter,
- [00:02:12.604]so our volume of solids is 57 centimeters cubed.
- [00:02:23.672]Well, perhaps we took a sample from a location
- [00:02:25.760]just to check if the density was ideal for our use.
- [00:02:28.784]The different uses do call for different densities
- [00:02:32.738]such as road construction or plant growth.
- [00:02:36.708]Okay, so all of these worksheet pages
- [00:02:39.150]will be relatively similar.
- [00:02:41.957]Got the formula here.
- [00:02:43.915]The snippet of data that we need over here.
- [00:02:47.467]And let us begin.
- [00:02:50.168]Bulk density is equal to the mass of solids
- [00:02:52.759]over the volume total.
- [00:02:55.366]Our mass of solids would be the dry soil,
- [00:03:00.817]minus the weight of the tin.
- [00:03:04.171]Our volume total is, in this case, 118 centimeters cubed.
- [00:03:10.509]So, 183 minus 32 is 151.
- [00:03:15.520]Over 118 is equal to 1.28 grams per centimeters cubed.
- [00:03:24.884]So, a mass per volume,
- [00:03:26.685]those are the appropriate units for a density.
- [00:03:32.255]Is this a typical bulk density value?
- [00:03:37.235]Yes. It is.
- [00:03:38.303]So, let us assume we've done this correctly and move on.
- [00:03:42.804]Particle density, remember now,
- [00:03:44.954]is going to still be in the same mass of solids
- [00:03:47.824]but then on the bottom, we'll use volume of solids.
- [00:03:50.452]Though the top will be done the same. Right?
- [00:03:53.518]183 minus 32 and now on the bottom,
- [00:03:57.824]we've got our volume of solids, 57.
- [00:04:09.570]2.65 grams per centimeter cubed.
- [00:04:13.840]151 divided by 57.
- [00:04:18.021]Like I said earlier, it's not too common
- [00:04:19.817]to actually measure your volume of solids
- [00:04:22.487]so instead we frequently assume a particle density
- [00:04:26.003]rather than calculate a particle density.
- [00:04:28.896]What is the assumed particle density for most soils?
- [00:04:35.259]Yeah, 2.65.
- [00:04:37.928]So, there is an example of calculating particle density
- [00:04:42.221]and bulk density for a given data set.
- [00:04:45.646]Remember, all densities are mass per volume
- [00:04:48.461]and grams per cubic centimeter is the units typically used.
The screen size you are trying to search captions on is too small!
You can always jump over to MediaHub and check it out there.
Log in to post comments
Embed
Copy the following code into your page
HTML
<div style="padding-top: 56.25%; overflow: hidden; position:relative; -webkit-box-flex: 1; flex-grow: 1;"> <iframe style="bottom: 0; left: 0; position: absolute; right: 0; top: 0; border: 0; height: 100%; width: 100%;" src="https://mediahub.unl.edu/media/5884?format=iframe&autoplay=0" title="Video Player: Soil Density Calculations" allowfullscreen ></iframe> </div>
Comments
1 Comments