 So in this video, I'm going to talk about grain-sized distribution or particle-sized distribution within soils. So we know that soils have a range of particle sizes and those can range from your boulder-sized particles, which is anything above 200 millimeters, your cobbled, which is anything above between 260 millimeters. And you have gravels, which are between 2 millimeters and 60 millimeters. And then there's sands, which is anything above 63 micrometers and 2 millimeters. And there's silt, which is anything above 2 micrometers and 63 micrometers. And then anything under that we talk called clay. So we have a range of particle sizes within soils. And we can measure that in a number of different ways. So anything above 63 microns, we can measure through sieving, either dry sieving or wet sieving, where we stack a series of decreasing apertures, sieves on top of each other, and measure the mass of your, put your sample into the top and shake it, and then measure the mass that's retained on each sieve. Anything below 63 microns, you can measure through sedimentation. And that involves, well first of all, sieving your sample through a 63 micron sieve, and then taking that fine material and immersing it in a liquid and measuring how quickly the the particles settle out. The way we represent that data is on a particle size distribution graph. And I'm just going to draw one up now. There are a number of different ways of representing the data, and I've put on my website, which is in the link below in the description, a ternary diagram that some soil scientists use to describe particle sizes within soils. And you might be able to see that there's a slight difference in the way that geotechnical engineers represent particle size distribution. So have a look at that link. And I'm just going to draw a typical particle size distribution on the board. Okay, so a typical particle size distribution graph might look something like this, where on the y-axis you have cumulative percent passing, which is calculated by essentially adding the mass that's retained on each sieve as you go down through the sieve stack and expressing it as a percentage of the total. And on the x-axis we have particle size. So let's take line A for example. What this is saying is that at, I don't know, something like 20 millimeters. So on the x-axis we have millimeters, so around 20 millimeters. 100 percent of the material is passing that size. Now as we move down through the line, and let's say we get to about 50 percent, we can say that 50 percent of the material is passing maybe somewhere around 2 millimeters. And then eventually we come down to maybe 10 percent as passing 0.1 millimeters. So that's really what this material, this graph is trying to communicate. And it's quite useful for showing a range of different particle sizes, or particle size distributions. So line A for instance, you might describe as something that's well graded. Well graded means that there's a wide range of particle size distribution. Whereas something that's more uniformly graded, like line B, well we describe that as uniformly graded. Now there's a rule for whether we describe something as uniformly graded or well graded, and I'll talk about that in a second, but the first thing to point out is that we'd from this be able to determine whether it's sand or gravel or cobble or a clay that we were talking about, and there's a set bunch of rules in the standard for doing that. And I'm not going to go through that in too much detail, but it's really just the proportion of the material that's that you would describe, that's within the sized class that you're talking about. So if you've got let's say 100 percent of your material is within the sand size class, then there's no real argument there that you're talking about a sand. If it's a hundred percent within the clay, then it's definitely a clay and mixtures between those two, or particle size distributions that fall between those two, you'd have a mixture of those descriptors, so a clay sandy clay or a silty clay or a sandy gravel. And I've put some links online and some resources on my website that help you create that classification. So line A we'd describe in this case as a course well graded sandy gravel, and you can kind of see that from just eyeballing the graph, you know, we know that gravel sizes stalled and here and sand is sort of around here somewhere. So we know that there's sand and gravel within this line A, so we're definitely sure that there must be a mixture between sand and gravel, and that's how we describe it. Line B, you see that all of the size fraction exists within the sand, so you can say that you've got a uniform, or sometimes that's called poorly graded and sort of the opposite of well graded, and it's either a sand or maybe if we've got some some of the size fraction within the silt classification, then it might be either a sand or a very slightly silty sand, so it could be a sand or silty sand. We can see that C has a lot of the, a lot of the material is, a lot of them what's even measured on the graph here, we can see that a lot of that is in the clay, so we can call that well graded because we've got quite a wide particle size distribution. And we can say that either a well graded gravel or a very clay gravel, it's because you've got a lot of the the particle size material within the clay fraction. And line D, well there's not really too much argument, we either have a silty clay or a clay, so D would be a probably a well graded. Now there's a formalised way of doing that, describing stuff as a sand, clay or gravel and do check out the link on my website. But how do we come up with a more robust way of determining whether these lines are graded or well graded or poorly graded? So there's a way to analyse that and I'll just go through that now, so I'll just clear this up. Okay, so to analyse whether a particle size distribution is graded or poorly graded, the way we do this is through two parameters, the coefficient of uniformity and the coefficient of curvature. And there's a bunch of other ones as well that you could determine. But really what they're trying to do is analyse the shape of this line to give you an idea of how broad the particle size range is. So the coefficient of uniformity is defined as the D60 over the D10. Now the D60 is the diameter at which 60% of the particles pass, so if we take 60% here, and let's say we're looking at line A, we go through to line A, our D60 would maybe be around eight millimetres, so in this case for line A it would be say eight millimetres. And then the D10 is the diameter at which 10% of the material passes, and let's say that's, I don't know, somewhere, 0.05. So for line A our coefficient of uniformity, C, U, would be 160. So what does that mean? Well, a C, U value of greater than 6 means that you've got something that's well graded. But be careful here because this changes depending on whether you're talking about a gravel or a sand, so just make sure that you've got that part of the classification worked out first. But so we can see that C, U is telling us, at least for line A, that all material is well graded. C, U of smaller than 6 is poorly graded. And that means essentially that the the limits here, the difference between D60 and D10 are getting smaller. So we're moving from a line A to something that's more like a line B. So we'd have something that would be poorly graded for line B. So the coefficient of curvature, which is CZ, is your D30 squared over your D10 multiplied by your D60. So the difference between these two is that coefficient of curvature is really trying to you to understand if there's any sort of dramatic changes within your within your particle size distribution. So things like gap-graded solos, it can be quite useful to deal coefficient of curvature. And it's giving you a point within this as well that gives you a little bit more information. A word of warning though is there's small changes in your readings here and that depending on if you if you're drawing this graph by hand or if you're analyzing it through through computer software can give you slightly different readings on your D60s, D10s and D30s. And that can have a quite a pronounced impact on the on the the results of your coefficient of uniformity or coefficient of curvature. So I suggest that you be careful about what you're putting into these equations and also round up as well and try and use a bit of common sense about interpreting these values.