 Hello, this is Dr. Mahesh Kalyanshetty, Associate Professor, Department of Civil Engineering, Valchand Institute of Technology, Swarapur. In this session, we will discuss about IS soil classification system. The learning outcome is, at the end of this session, students will be able to classify the soil in accordance with IS 1498-1970. Now, let us see what are the purposes of soil classification. The soil classification system is established to help people predict soil behavior and to provide a common language for soil scientists. Another purpose is to arrange the various types of soil into groups according to their engineering or various other characteristics. And the soil possessing similar characteristics can be placed in the same group. So, the purpose, the sole purpose of all this soil classification is to group the soil into different categories based on their properties. There exist many soil classification systems. This is a list. The first one is the particle size classification wherein the classification is made based on the particle size. Second one is the textural classification. So based on the texture of the soil, the classification is made. Third one is the heavy research board, HRB classification. It's a British system. Then fourth one is unified soil classification system. And fifth one is Indian standard classification system. So, we will focus on the Indian standard classification system. Prior to that, we will also discuss the soil classification system based on the particle size. So particle size classification, here the classification is made based on the particle size of the soil particles. So, the soils are arranged according to their grain size. The terms such as gravel, sand, silt and clay are used to indicate the grain sizes. And these terms are used only as designation of particle sizes. They do not signify naturally occurring soil types. And naturally occurring soils are mixture of particles of different sizes. So this is what is the IS classification as per IS14981970. So based on the soil particle size, the classification is made. Now you can see here, the particles finer than 0.002mm are called as clay. And then from 0.002mm to 0.075, it is called as a silt. And from 0.075mm up to 4.75, this particular soil is basically a sand. And in the sand, again, division is made based on the size. So it's a fine-grained soil up to 0.425, medium-grained soil up to 2mm. And then the coarse-grained soil. Then the particles having a size more than 4.75 is called as a gravel. Up to 80, it is a gravel. And here again in the gravel, we have two categories. One is called fine gravel, another is coarse gravel. So based on this particle size, beyond 80mm up to 300mm, the particles are called as cobalt. And beyond 300mm, it is called boulder. So let us move to the IS soil classification system as per 1498-1970. So as per this IS code, the soil is classified into two categories, basically. One is called coarse-grained, another is called fine-grained. However, if you have a high organic content, so that it can be separately classified as highly organic soil. So as far as the inorganic soil, we have two categories, coarse-grained soil and fine-grained soil. So coarse-grained soils are the soil where we have 50% or less material is passing 75 micron. And fine-grained soil is more than 50% passing 75 micron sieve. Now let us concentrate on the coarse-grained soil. So in the coarse-grained soil, again, we have the two types. One is called gravel, another is sand. Now this distinguish we can make based on the sieve analysis. You can see that the percentage of material retained on 4.75. So based on this percentage, we can classify whether it is gravel or sand. And if it is a percentage of coarse fraction retained on 4.75 mm sieve is greater than 50%, it is called gravel. And if it is less than 50%, usually it is called as sand. Now further, we can have a classification of the gravel and sand. So in the next slides, we will see how the gravel is further classified. So here, gravel is again further classified. So based on, again, the fine materials present in the soil. So if you have less than 5% passing 75 micron sieve, then we have the two options. Less than 5% passing 75 micron sieve, it means we have a very, very fine, a very small amount of fines present. This is regarding the fines, means percentage passing 75 micron. So we have two possibilities, well-graded or poorly-graded. So this can be identified based on the criteria given. And we have some specific criteria for well-graded and poorly-graded soil that we will see in the other presentation. So if it is well-graded, then it has been given a symbol as gw, g stands for gravel and w stands for well-graded. And if it is poorly-graded, it's a symbol is gp, that is gravel and p is poorly-graded. But if the fines are between 5% to 12%, you can see here, passing 75 micron sieve means what these are called as the fines. If the fines present are in between 5% to 12%, it means that substantial quantity of fine material is present, therefore we cannot neglect those fine materials. And for that, we have to see A-line chart, which has been given by IS code. So this chart is also called as A-line chart or plasticity chart. So here based on this particular graph, now if liquid limit and plastic limit, based on our liquid limit and plastic limit, if our point comes out above A-line, then it is called as a clay below A-line, it is a silt. And if the point is in the hatched zone, it is a combination of silt and clay to see whether it is above A-line or below A-line. So if it is above A-line, it is gc means gravel consisting clay particles. If it is in the hatched zone, then you can see silt and clay both are present. It is gm, gc. And if it is below A-line, it is silt, therefore it is gm. So in the same thing is for sand. Now for the sand also, we can see the classification is of same nature. So here also we classify the sand further based on the final material, whether it is less than 5%, 5 to 12% or more than 12%. And the same system we follow here as it has been followed for the gravel. Only thing you can see here, instead of g, we find s, s everywhere. This is what is the change. Now I will request you to take a pause and solve this problem. A soil sample has 72% of mass retained on 75 micron Sioux. Out of this, 55% of mass is retained on 4.75 mm Sioux, classify the soil. So take a pause and classify the soil. Welcome back. Hope you have come up with the solution. So this is what is the problem. So we know that just now we discussed in the earlier slides that based on the 75 micron Sioux, so it is more than 72%, means more than 50% is retained. Therefore it is basically a gravel or it is a coarse grained soil basically. Then again on 4.75 also more than 50% is retained and therefore it is a gravel. So based on this flow chart, we can very easily identify that the given type of soil is gravel. Let us come to the classification of the fine grained soil. Now for the fine grained soil, you can see here, now coarse grained soil, we just now finished. Now come to the fine grained soil, it is more than 50% passing 75 micron Sioux. It means that all the particles are of very fine size and in such cases the classification is totally based on a line chart or plasticity chart. So this is called as a plasticity chart. In the plasticity chart we see that on x-axis there is a liquid limit plotted, on y-axis there is a plasticity index and we have certain lines plotted here. So this inclined line is called as a line which has got this equation which is given here and apart from this line we have two vertical lines, one is at liquid limit 35, another is at liquid limit 50 and we have the hatched zone here for a plasticity index 4 and 7. So in between this we have the hatched portion. So this particular lines divide this area into number of segments and above the inclined line, above the A line all the soil is a clay. You can see here the C, C, C everywhere and below A line it is a silt and whenever we come across with the hatched zone it is a combination of clay and silt. At the same time below 35, liquid limit 35 it is a low compressible soil, liquid limit 35 to 50 it is a medium compressible and beyond 50% it is a high compressible soil. So based on this some symbols are given. So we can see here in this zone it is C, C means clay low compressible. This is C, intermediate compressible because it is in between these two lines and this is C that means clay with high compressibility. In the same way below A line we find the silt everywhere. So it is MH or organic soil. This is MY or organic soil and this is ML or organic soil. So in this way we can have different segments here. Now what we have to do is based on our properties, based on our data we have to see where our point comes. So if it comes in this particular segment then our soil is a MH step of soil. If my point comes in this particular zone then it is called a CH type of soil that means clay with high compressibility. So this we will discuss with the help of small problem. So let us take one example. So classify the soil with following data. So passing 75 micron is 68%, liquid limit is 45%, plastic limit is 20%. So therefore now since it is more than 50% passing 75 micron therefore it is a fine grain soil therefore we have to refer the A line chart. And now find the liquid limit, it is my point comes here so as it is shown by B here. So this point is now in the zone of CI we can see. Therefore my soil is clay with intermediate compressibility. So these are the references used for the presentation. Thank you.