 Welcome to module number 1, lecture number 8 of advanced geotechnical engineering course. So in this lecture we are going to introduce ourselves to soil compaction and we will discuss this in two lectures. Before discussing soil compaction 1, we will try to do some example problems based on the previous lecture that is based on soil classification. We have discussed about activity which is nothing but ratio of plasticity index to percentage clay fraction and we said that this can be used for classifying some expansive soils. So if you look into this slide after Bell 1993 a plasticity index and clay fraction which is less than 2 micron is plotted and here different degrees of expansions are indicated very high expansion somewhere in this zone and high expansion, medium expansion and low expansion. So the swell shrinkage response of a clay depends upon the period and magnitude of precipitation and evapotranspiration which actually takes place. If you look into the minerals, kaolinite has got the smallest swelling capacity and illite may swell up to 15% and intermixed illite and mantle monolite can may swell up to 60 to 100%. And as we discussed earlier the swelling of calcium mantle monolite can be there up to 50 to 100% and sodium mantle monolite can be as high as 2000%. So the swell shrinkage response of a clay depends upon the period and magnitude of precipitation and evapotranspiration which actually takes place in the ground. So let us take this example one. In this example we have been given for a soil specimen that percentage passing 2 mmc is 100% and percentage passing 0.425 mmc is 85% and percentage passing 200 c that is 75 micron c is about 38% and liquid limit of given soil is 20% and plasticity index is 12%. So what we need to do is that classify the soil by the unified soil classification system. The solution for the example one works out like this. The soil is a coarse grained soil the percent passing is less than 50%. Like if you look into the previous slide passing 200 c is less than 38%. So soil is a coarse grained soil whereas the fines are less than 50%. Since percentage of coarse fraction passing number 4 c is greater than 50. Since more than 12% passes 200 c it must be sm or sc and with plasticity index is equal to 20 minus 12 8. So up to 7 we said that it can be just right below the a line so this indicates that for the given liquid limit of say 20% and plasticity index of 8 it is slightly above a line. Hence by using the Casagrande's plasticity chart we can classify the soil and then above criteria what we discussed as sc. Let us take another example 2 here in this soil sample passing number 4 c is 92% that means that number 4 c is nothing but in particle sizes it is 4.75. So particles passing size of the particles or the fraction of the particles passing 4.75 mm c is 92% and passing number 40 c that is nothing but 0.425 mm c is 78%. And passing number 10 c is nothing but 2 mm size is 81% and 200 c is nothing but 65%. So you can see that the percentage fines are more than 50% and liquid limit is 48% and plasticity index is 32%. So we need to classify the soil according to unified soil classification system. So based on the given data since more than 50% is passing through a number 200 c it can be it is a fine grained soil however it could be ML or Cl or OL MH OH CH or OH. So if you plot liquid limit 48 and plasticity index 32 on the plasticity chart it falls in the zone of Cl so which is liquid limit greater than 30 and which is less than 50. So it is actually falls on the zone of Cl. So the classification for the soil based on the given data is Cl. In the example 3 limit test performed on a clay indicate a liquid limit of 67 and a plastic limit of 32. From a hydrometer analysis the percentage fines the determine the particle sizes it is found that 80% of sample consists of particles smaller than 2 micron 0.002 mm from this information we need to do indicate the activity classification and the probable type of clay mineral. So we have been given liquid limit and plastic limit so we can actually get the plasticity index and we have been given percentage clay fraction which is about 80%. So we need to indicate the activity do the activity classification and probable type of clay mineral can be suggested. So based on the data the plasticity index is about 35 and so area the activity is calculated as 35 by 80 which works out to be 0.44. So the clay mineral is with the activity in the range of say 0.3 to 0.5 is said to be kaolinite. So the clay mineral can be as kaolinite. In this example by using the grain size distribution curve shown below like soil A and soil B are given and soil B has the atterberg limits of liquid limit 49% and plastic limit of 45%. So the plasticity index is about 4%. So we need to classify the soil A and B using unified soil classification system. So based on the given data once we draw the grain size distribution curves soil A we spawn to have 2% gravel fraction and 98% sand fraction and 0% silt fraction and 0% clay fraction. So the soil A what we see is this one and soil B which is actually having 1% gravel fraction and 61% sand fraction and 31% the silt fraction is indicated by letter M and 7% clay fraction. In soil C which is for another example but however it is represented here for comparison purposes. Soil C 0% gravel, 31% sand and 57% silt and 12% clay. So the gradation of soil A, soil B and soil C is given in this particular slide. So for soil A as indicated in previous slide the gravel fraction is 2% silt a sand fraction is about 98% and silt fraction is 0% and clay fraction is 0%. By calculating Cu which is nothing but D60 by D10 which can be obtained from the chart here D60 the particular size which can be referred here similarly D10 for soil A can be referred like this. Once we obtain this we can actually calculate Cu and Cc. As can be seen that Cu is 2.8 and Cc 1.29 so based on the criteria discuss the soil A is a poorly graded sand or which is also said as uniformly graded sand. For soil B G is equal to 0%, S is equal to 61% and silt content is about 35% and clay fraction is 4%. So with this Cu which comes to be 90 is very high so this indicates that this is a very well graded silt sand SM. So based on the liquid limit data also if you look into this the plasticity index is about 4% and it is below the A line it falls actually below the line so that is why it is actually called as SM type. Now having understood about the soil classification let us try to introduce ourselves to the topic of today's lecture that is soil compaction or compaction of soils. The soil compaction is very important because for majority of the geo structures or the structures which are actually constructed on soil the soil is actually used as a construction material. For example highway embankments, railway embankments, earthen dams, canal bunds, highway airfield pavements and backfill trenches and for closing some landfills soil is actually used as a construction material. So there is always a requirement in some cases the soil compacted soil has to give the adequate load carrying capacity. In some situations the compacted soil has to act like a barrier in preventing ingress of water into the uncompasted waste. So when soil is used as a foundation material it is desirable that in place material possess certain properties. So the purpose of the compaction is to produce a soil having physical properties appropriate for a particular project as I said earlier. So depending upon the type of the project the purpose of the soil compaction is basically to produce a soil having physical properties appropriate for a particular project. So the compaction how do you define is basically defined as the process of increasing the unit weight of soil by forcing the soil solids into a dense state and reducing the air voids. So here this is a process of increasing the unit weight or packing the soil particles into the denser configuration and reducing the air voids. Practically in this process no change in the volume of water in the soil is noted. So no significant change in the volume of water in the soil will be there. And this is achieved particularly the process of the compaction can be achieved by applying the static or dynamic loads to the soil. So compaction is measured qualitatively in terms of the dry unit weight of the soil. So if we are able to achieve the desired unit weight then we can say that the soreness of soil is compacted to a desired degree. So the compaction is nothing but the process of increasing the unit weight of soil by forcing the soil solids into denser configuration and reducing the air voids. So reducing the air voids means that there is a possibility of the expulsion of the air takes place. So compaction generally leads to you know it increases the shear strength. This means that when you have what the soil which is compacted properly then this means that the larger loads can be applied to the compacted soil since they are typically stronger. So increase in shear strength so the compaction of a soil lead to increase in shear strength and reduces compressibility. This also means that the larger loads can be applied to compacted soils since they will produce smaller settlements. So the soil say uncompacted soil can actually experience larger settlements. So this means that the larger loads can be applied to compacted soils since they will produce smaller settlements. And also compacted soil inhibit the movement of water. That means that they inhibit the soils ability to absorb water and therefore reduce the tendency to expand, shrink and potentially liquefy. So the compaction process to the soil has got several benefits. One is to it induces increased shear strength, reduces compressibility and reduces reduced permeability. So the reduced permeability basically this inhibits the soils ability to absorb water and therefore reduce the tendency to expand, shrink and potentially liquefy at the onset of shock loading. Why do we need compaction? The purpose of compaction if you look into it as you said in the previous slide maximum shear strength occurs approximately at a minimum void ratio. Minimum void ratio is nothing but which is actually a void ratio at which the particles are actually packed as close as possible and large air voids may lead to compaction under working loads and causing settlement of the structure during service. So under working loads the larger air voids may lead to compaction and causing settlement of the structure. So the larger voids if left may get filled subsequently with water and they tend to reduce the shear strength of the soil. Increase in water content is also accompanied by swelling and loss of shear strength in some place. So increase in water content is also accompanied by swelling and the loss of shear strength in some place. So when you have a compacted soil without with larger voids it leads to increase in water content and this can lead to swelling and then loss of shear strength in some place. changes by compacting the soil we can reduce settlements or we can prevent and soil strength increases and stability can be improved and load carrying capacity of the pavements of grades especially for highway pavements or air field pavements the sub grades can be improved and undesirable volume changes can be avoided like frost action or swelling or shrinkage may be controlled undesirable volume changes may be controlled. So these are the advantages of compaction. If you look the compaction as a technique as we said that is the process of densification and it leads to the reduction in the volume of air voids and it is an almost instantaneous phenomenon and the soil is always remains to be partially saturated and typically applies to all soils that are applied or reapplied to construction site. And if you look the compaction as a technique is a old technique adopted in ancient China and India. So compaction is a old technique adopted in ancient China and India countries. So as we discussed there are two predominantly two types of soils one is cohesion less soils and other one is cohesion soils. So if you look the process of say compaction of cohesion less soils when speaking of cohesion less soils we have gravelly soils or sandy soils then we knew that there are different types of particular arrangements or soil fabric. So a loose angular soil may have the so called arrangement like this and when it is compacted or densified the dense angular soil will have the so called the particular arrangement. And in certain type of sandy soils the under little moist conditions it will have honey combed soil and very loose in nature or we have a loose matrix of soil and this can actually lead to with compaction with adequate densification the possibility of arriving at densification with this particular type of soil fabric arrangement. So the soils in loose or honey combed state or avoided are compacted before being built upon since they are prone to densification when subjected to vibratory or shock loading. So as from the earthquakes or vibratory machinery so the soils in loose or honey combed state are required to be avoided and are compacted before being built upon. So for example if I have got a soil with H0 as the initial thickness and upon compaction the E0 changes to EF if it is actually closer to the proximity of even more of a given soil then the delta H which is actually a reduction in the thickness which is resulting due to the compaction process the delta H is equal to H0 into E0 minus EF which is nothing but the change in void ratio from E0 to EF divided by 1 plus E0 which is nothing but the original void ratio. So the thickness can be calculated by which is nothing but delta H by H0 which is nothing but the change in length by original length to change in void ratio divided by the 1 plus E0. The compaction of cohesionless soils the relative looseness of a soil in its natural or in-situ state is determined by measuring or computing its relative density that is d suffix r and this we have defined as d suffix r as emax minus e divided by emax minus eminimum, emax is nothing but the maximum void ratio in the loosest state, eminimum is the minimum void ratio for a given soil in the densest state, e is nothing but the in-situ void ratio. So the smaller the relative density for a given soil deposit the more prone the soil deposits to will be densification and settlement that means that the smaller the relative density for a given soil deposit the more prone is for the settlements. For uniformly or poorly graded spherical grain soils the theoretical range of void ratios if you see the uniformly graded soils the theoretically the range is 0.35 to 0.9, 0.35 to 0.9 is the void ratio range for the uniformly graded soils. In case of say well graded soil let us say sub angular sand the theoretical range of void ratios minimum and maximum is 0.35 to 0.75 and 0.25 to 0.65 for well graded silty sand. So the range of the void ratios for well graded soils is less than that for uniformly graded soils. So if you note down here the range of void ratios for well graded soils is less than that for uniformly graded soils. That is why it is generally preferred to use well graded soils in geotechnical applications as opposed to uniform soils because here the range of void ratios for well graded soils is less than that for uniformly graded soils. So that is why it is generally preferred to use well graded soils in geotechnical applications as opposed to uniform soils. Compaction soils particularly compaction of cohesion less soils can be carried out by vibration only and if you apply a static load it produces very little compaction to the loose sand and medium and fine sands do not get compacted easily when moist because of the shear strength developed by the capillary forces. So when you have got the medium and fine sands they do not compacted easily when they are moist because of the shear strength developed by the capillary forces. In the when these sands are moist in condition the water which is actually there under that moistness develops a thin film surrounding these particles and it prevents and it applies capillary forces and that induces actually very high strength and that makes the very difficulty to compact these soils particularly medium and fine sands when they are under moist conditions and dry or submerged sands can be compacted easily by vibration. High sand or submerged sands water submerged sands can be compacted by vibration. So in the previous slide we have noted that cohesion less soils can only be compacted by vibration contrary to this clay soils cannot be compacted by vibration shaking the vibration does not change you know volume. So very small amount of static pressure produces a large volume decrease of the platelet particles or if you have got mica flakes very small amount of static pressure application induces a large volume decrease. So in compacting the clay the position of particles must be changed by forcing the contact points along the adjacent surfaces to positions nearly parallel with the reduced voids. So in the process of compaction of the clay the clay particles undergo rotations and they they actually almost take the positions of almost like parallel orientation. So the clays cannot be compacted by vibration and very small amount of static pressure is sufficient to have a you know considerable amount of decrease in the volume. So in this slide if you look into this as you all know that we have learnt that the clay particle is surrounded by adsorbed water which is actually with you know strong attachment of thick viscous liquid surrounding the clay particles and then it is covered by absorbed water or free water. So in this case what will happen is that the thickness of the absorbed water and free water is function of water content. So here this is in the platelet particles in the loose structure of the clay before compaction and this is the dense structure of the clay after compaction. So this can be achieved by applying adopting appropriate compaction technique in the field. So when the clay has a high water content less than saturation let us say a thick layer of free water surrounds the particles. So as we seen that clay particles are surrounded by you know adsorbed water so thick layer of free water surrounds the particles. So under this condition only a small amount of pressure is required to force the particles into new positions but a degree of high degree of compaction cannot be produced with this high water content because this thick layer of free water prevents the particles from being forced close together. So this high amount of thick layer of free water also prevents the particles from coming closer. So in this process before discussing about the field compaction methods let us actually look into you know the proctor theory wherein the process of actually compaction has been defined by RR proctor in 1930. So proctor showed that there exist a definitive relationship between the soil moisture content and the degree of dry density or unit weight to which soil may be compacted and that for a specific amount of compaction energy applied to the soil there is one unique moisture content and that is referred as optimal moisture content at which a particular soil attains maximum dry unit weight. So the proctor postulated that upon application of a specific amount of compaction energy on the soil that there is a unique moisture content which is actually called as optimum moisture content at which a particular soil attains maximum dry density. So proctor proposed test to determine relationship between water content, dry unit weight or void ratio of a compacted soil in a standard manner and to determine optimum moisture content and dry unit weight of the soil. So compaction is a function of dry unit weight of the soil compact to effort that is the amount of energy applied to the soil and the soil type. So if you look the soil type we knew that the gradation presence of clay minerals etc. So the compaction of a soil is found to be a function of several factors and some of the factors which are actually listed down are here. So compact to effort is a measure of mechanical energy applied to a soil. So we will be using this particular technology compact to effort. So the compact to effort is defined as a measure of mechanical energy applied to a soil mass. So in the laboratory the two methods have been devised. One is standard proctor compaction test and modified proctor compaction test and as per the Indian code it is also called IS light compaction and modified proctor test is called as highest heavy compaction. So it has been thought that for achieving higher densities at low moisture contents and this was actually thought to be possible basically for constructing highway in highway and air field applications the modified proctor compaction test was actually developed. So the scope for the standard proctor test is that this method basically covers the determination of relationship between the moisture content and density of soils compacted in a model at a given size with 2.5 kg rammer. So about 2.5 kg of rammer dropped from a height of 3.305 mm. So here the number of layers which are actually involved in a mold of fixed size where 3 layers which are actually required to be compacted with an energy of say 2.5 kg into the drop weight of about 0.305 meters or 305 mm this is a free drop height. So the compactive energy can be calculated for in case of standard proctor compaction test it is like this which is compactive effort is nothing but 25 which is nothing but the number of blows, 3 small and then nothing but the number of layers as I said that it is 3 layers and weight which is nothing but 2.5 kg that is weight of the hammer and height of drop in meters it is 0.305 divided by 10 to the power of 3 and 10 to the power of minus 6 I will get about 57187.5 kg meter per meter cube or 594 kilo joules per cubic meter. This is actually the energy which is applied in standard proctor compaction in the laboratory. So the calculations which are actually involved is that once we know when the given soil once we take when you start increasing the water content you will actually measuring the bulk unit weight of the soil at each water content once it is compacted. So at each stage we will be noting down bulk unit weight that is weight by volume and once by determining the water content we can get the dry unit weight of the soil gamma ds gamma bulk divided by 1 plus w. So we will be able to calculate for a given water content what will be the different dry unit weights. So once you plot these things you will have a normally a bell shaped curve with a peak at a predominant point the portion with the peaking of the curve occurs that is actually on the y axis it is referred as maximum dry unit weight on the x axis it is referred as the water content that is nothing but the optimum moisture content or optimum water content. So as we discussed here typically for a given soil we have got gamma d1 and for that water content w1 and for a given water content w2 where w2 is actually more than w1 then we have got gamma d2 and then there is one particular water content at which you know the density was high the unit weight was high and then there is a decrease in the density. So if you see that you have got dry to the optimum so this is actually called as optimum moisture content so this is called the dry side of optimum and this is called the wet side of optimum and these are actually called as you know zero air voids line so the zero air voids line is nothing but 100% saturation line. So this is a hypothetical line what you can see is a hypothetical line and the downward limb of the towards the wet side of optimum and the zero air voids line can never coincide because 100% you know expulsion of air is not possible. So the soil in this case remains always in the partially saturated state only. So this is the you know a definite compaction mode and the in the given area the each and every location the energy has to be supplied uniformly by dropping this 2.5 kg hammer at the drop weight of 0.305 meter like this which is actually shown in this slide. So here what actually happens is that this actually make the soil is actually compacted uniformly. So if you look into this there is a region where there is increase in the density where the water content actually continues to increase upon increase in certain water content beyond this so called optimum moisture content what we are seeing is that the same soil mass is experiencing the decrease in the dry unit weight of the soil. So the principle of compaction and moisture density relations if you look into this compaction of soil is achieved basically by reducing the volume of voids that is what we have discussed and it is assumed that the compaction process does not decrease the volume of solids or soil grains. So the compaction process does not decrease the volume of solids volume of solids remains to be same what is actually changing is that the volume of the voids where in the air density is actually expelling out of the voids for example here this is the portion of the soil which is uncompacted and this is the compacted or this is a particular arrangement which is uncompacted and in a dense and configuration which is actually shown here. The degree of the compaction of a soil is basically measured by the dry unit weight of the soil skeleton the dry unit weight can be computed basically because they know that dry unit weight basically correlates the degree of the packing of soil grains so if you can recall the dry unit weight can be given by gamma d is equal to gs gamma w by 1 plus e so the more the compacted soil is the smaller is the void ratio will be and then higher will be the dry unit weight. So the smaller is the void ratio and the higher will be the dry unit weight. So the degree of the compaction of a soil is basically measured by the dry unit weight of the soil skeleton and the dry unit weight correlates the degree of the packing of the particles in a given volume. So if you look into this as we said that in the previous slides we have when we plot gamma d that is dry unit weight with water content and as the water content is added to the soil mass there is an increase in the density at a certain point there is a decrease in the density takes place. So for a normal soils the water plays a critical role in the soil compaction process it actually depends upon the type of soil. So it lubricates that soil grains so that they slide more easily over each other and can thus achieve a more densely packed arrangement. So water which we are actually supplying in the process of increasing the water content to the given soil mass the water actually acts like a lubricating agency. So make the soil grains to slip into the denser configuration while a little bit of water facilitates compaction and too much water also inhibits compaction that is what we have seen on the wet side of optimum towards the wet side of optimum upon adding water we have seen that there is a decrease in the density of the soil mass. So what is actually the mechanism which is actually happening if you see here water actually helps the compaction here and water actually hinders the compaction. So this is the zero air voids line so theoretically this is the maximum degree of compaction so which is also called as the this is a hypothetical line. So here water is actually helping the compaction here water is actually hindering the compaction. So if you look into this at low values of water content most soils actually tend to be stiff and are difficult to compact. So as the water content is increased soil becomes more workable because of the lubrication actually provided by the water facilitating the compaction and resulting in the higher densities. So as the water content is increased the soil becomes more workable and facilitating the compaction and then resulting in the higher dry densities or dry unit weights. At higher water contents what is actually happening is that the dry density decreases with increasing water content that is what actually we are seeing here on the wet side of optimum. This is the optimum water content so on the wet side of optimum there is a decrease in the dry density. This is because with increasing water content and increasing proportion of the soil volume is now being occupied by the water. So as we are actually increasing the water the increased proportion of the water is being occupied by the soil volume the an increasing proportion of the soil volume being occupied by water. So because of this as we know that rho w that is mass density of water is much less than rho s because of that what will happen is that the density decreases. So what we see is that at low values of water content the most soils tend to be stiff and are difficult to compact as the water content is actually increased the soil becomes more workable and facilitating for compaction. So the principle of the observed phenomenon is actually explained in this particular slide. So this is you know uncompacted soil which is actually shown in a three phase diagram. So throughout the process of compaction it actually remains in three phase state and this is actually in practice the dry weight is never achieved but it represents the theoretical upper bound value. So complete removal of air which is actually not possible but this is theoretically maximum degree of compaction which is actually possible. So once we get this relation of dry density or dry unit weight with water content and once we have maximum drain weight and maximum optimum water content we can actually construct this air voids lines or you know 0% air voids line or we can also construct 100% saturation line both are same. So this is actually possible by for the saturation lines can be obtained by this relation gamma d is equal to gs plus 1 plus wgs by sr into gamma w. Here when sr is equal to 1 that is in case of say 100% saturation line then the equation for that is nothing but gamma d is equal to gs gamma w by 1 plus wgs. So here if you look into this at optimum moisture content and maximum dry unit weight the soil has got 80 you know normally for 80 to 90% of degree of saturation. And similarly in another terminology we can also write we can also draw air voids lines air void lines is nothing but air void percentage air voids can also be defined as volume of air in the total volume of the soil mass air content is nothing but volume of the air in the volume of voids. So here gamma d is equal to gs into 1 minus na plus 1 plus wgs into gamma w, na is equal to n into 1 minus sr and na is equal to naac by using this we can actually get these you know saturation lines and air void lines plotted. So this is explained once again the saturation line is an hypothetical line and points and the line denote the density for completely saturated condition at respective water contents. It is basically it is the maximum possible dry density for any soil and practically it is not possible to achieve this density and the dry density for saturation line can be obtained by this particular expression as we discussed already. Then as we discussed that there are also another test one is that standard proctor compaction test then for in order to achieve higher densities modified proctor test has been devised by ASTO which is actually widely adopted by U is developed by US Army Corps of Engineers developed the modified proctor test which used greater levels of compaction and produced the higher dry densities. So modified proctor test was later adopted by ASTO and ASTM. So in this modified proctor test we have number of blows that is remains constant 25 but instead of three layers in standard proctor compaction test the modified proctor compaction test has got five layers and the weight of the hammer is 4.5 kg in comparison with standard proctor compaction test it was 2.5 kg and the falling height is 0.45 meter. So what we are actually doing is that we are actually supplying about 4.5 times the energy. So if you look if you calculate the energy or the applied to the in the modified proctor compaction test the compactive effort is actually about 25000 3125 kg meter per meter cube. So this is actually approximately 4.5 times the energy supplied in the standard proctor compaction test. So here with increase in compactive effort this is with IS light compaction and this is with heavy compaction. So if you can see that with increase in compactive effort there is a decrease in the optimum moisture content and increase in the density. So there is a possibility that with increase in the compaction for a given soil is possible for us to achieve denser configuration that means that by applying the higher energy to the soil the possibility of achieving denser configuration is seen. And however applying higher energy to say moist soils or completely saturated soils can also lead to advantages and more than certain amount of energy also may not be desirous. So the importance of the proctor test is that it gives the density that must be achieved in the field. Once we have a given soil which has been selected for the construction it gives the density that must be achieved in the field and provides the moisture rain that allows for the minimum compactive effort to achieve the density and provides data on the behavior of the material in relation to various moisture contents and it is not possible to determine whether the density test passes or fails without it. So once we have the data and once we verify the density achieved in the field then it is possible for us to achieve to assess the degree of the compaction which is actually achieved in a given soil. Now if you list out the factors influencing the compaction there are as we discuss soil type is one of the predominant factor then moisture content. Suppose if you have got a sandy soil and if it is moist in nature it actually exhibits a certain phenomenon and upon increasing the moisture content you know it behavior changes. See when you have got soil type then depending upon whether it is a CL type of soil or CH type of soil or if you have got a well graded soil so there is a possibility of the influence on the compaction and effect of the compactive effect. We have just now discussed that increasing compaction energy reduces the optimal moisture content because what is actually happening is that the applied energy makes the particles to adjust into the denser configuration. So it facilitates the particle rearrangement and at low moisture content itself and the effect of compactive effort is again subdivided as the nature of effort like load duration in the area of the contact. So sometimes for some soils the area of the contact plays very crucial role and effect of the compactive effort is nothing but amount of effort what is how much is actually being applied to the soil. So soil type which is again grain size, shape of the soil grains, amount and type of minerals present and that Gs of soil solids have greater influence on the dry unit weight and optimum moisture content. Suppose if you have got a poorly graded sands that is say uniformly graded sands initially there is a decrease in the moisture content and then increases to a maximum value with further increase in moisture content. So if you see at low moisture contents there is a possibility of capillary tension which actually inhibits the tendency of the soil particles to move around and compacted. So what will happen is that at low moisture contents the soil density decreases and upon increasing the moisture content what will happen is that the soil fillings which are actually surround the water fillings which are actually surround in the grains get washed or diminished. So that makes the soil particles to again rearrange into the tensor configuration. So this particular phenomenon which actually happens in certain type of sandy soils is actually called as bulking factor, bulking phenomenon and this is actually owed to the capillary phenomenon. So here in this particular slide if you can see that the compaction curves for which different soil types is shown here what you see is for this is for uniform sand. In fact for a sand there will be a decrease and then increase. So what you are seeing is for the uniform sand and if you see here clay of high plasticity and then clay of low plasticity. So clay of low plasticity can actually has got higher densities and low moisture contents and clay of high plasticities have low dry densities and higher optimum moisture contents. Similarly the sandy clay and well graded sand, well graded sand can have higher dry unit weights and lower optimum moisture content. Similarly gravel sand clay mixers it actually can be placed somewhere here. So the compactability or ease with which the soils can be compacted will majorly depend upon the type of soil. So if you note in the previous slide at a given moisture content a clay with low plasticity will be stronger than heavy or high plasticity clay as it will be easier to compact. The basic reason is attributed like this for a given compact effort the air voids can be removed more easily for a low plasticity clay and because it will have low moisture content anyway higher dry unit weight can be achieved. So this is you know the major reason what we actually have seen. So in this particular curve once again it is shown here a CH type of soil and a CL type of soil and this is for ML type of soil and SWU well graded sand well graded gravel. So you can see here that these are the you know degree of this is air content lines 0%, 5% and 10% lines. From the fundamental definitions the 0% air content line or the 5% air content line and the corresponding degree of saturation line they are different. So the effect of compact effort if you look at the amount of compact effort maximum dry unit weight increases with increase in the compact effort and increase in the compact effort decreases optimum moisture content to some extent. So here when you increase the compaction energy like from 20 blows, 25 blows or 30 blows or 50 blows then there is a possibility that so this particular you know as we can see with increase in compaction energy there is a shift in the compaction curves. So this particular you know as we can see with increase in compaction energy there a shift in the you know the compaction curves towards left hand side with increase in dry densities increase in compaction energy leads to decrease in the optimum moisture content. So the line joining the maximum dry unit weights and optimum moisture contents is called line of optimums. So this is the so called the line of optimums so it is also referred for some certain applications like low proctor compaction. So in this low proctor compaction what we do is that in order to simulate the poor compaction conditions we apply you know 15 number of blows only and the standard proctor means 25 number of blows and modified proctor compaction means sometimes even 15 number of blows. So applying more energy to soil will reduce the air voids content and further increase the dry unit weight and more compaction energy can be beneficial especially for soils which are actually dry set of optimum and wet set of optimum which is not possible because that can actually lead to the increase in the pore water pressures and all. So if a soil is already moist weaker and above moisture optimum moisture content then applying more energy is wasteful as because air can quickly be removed and applying large amount of energy to a very moist soil may be damaging since because no more air can be expelled but high pore water pressure can build up which could cause. So these build up high pore water pressure can get actually locked and can lead to the slope instability problems during construction and also can lead to the consolidation settlements as because the once the pore water pressure which is actually locked inside can dissipate and the settlements can be resulted. So the effect of the compact effort means nature of effect load duration and contact area so longer duration leads to reduced shear stiffness response and greater compound greater compaction and greater contact area leads to the greater depth of influence. So that is also what we said is that effect of the compact effort is also the nature of the effort the load duration and contact area also is. So degree of compaction energy degree of compaction generally increases the increasing the compact effort that we have discussed already. So here if you look into this the applying more compact efforts to the soil is also not much beneficial if you can be noted here the increase in the dry unit weight is marginal. So this is actually moisture density relationship of the cohesion less soils is shown. So this is actually what actually at point C what is actually happening is that these water films which will actually prevent the particles to come into the denser configuration and because of this thin water films it actually has got the low density. But upon adding more water to this same soil the thinning of the films takes place that makes or you know the density increases here. So that is the reason why here there is a decrease in the density and then increase in the density that this particular phenomenon is actually described in this slide. So the surface tension forces induces this effect to apparent cohesion strength the resist in the compaction initially decreasing the dry density. And if you look into the effect of compaction on the soil structure so here if you look here there are A at point A the soil is actually highly flocculated and at point A the soil is in a dispersive state. So upon the increase in water content if you see the particles are actually undergoing the clay particles are undergoing degree of rotation. It is said that these clay particles undergo about you know 60 degrees rotation. So at optimum here if you see the soil will actually will have you know partially flocculated and partially dispersed and here because of this it is something the flocculated nature the strength of the soil is high and there is a possibility of the higher permeability and lesser shrinkage and more swelling because and then here the low strength because of the high water content and because of this dispersive nature there is a low permeability more shrinkage and less swelling. So in this lecture what we try to understand is that some example problems we actually solved for based on the classification of soils what we discussed in the previous lecture and then we introduced ourselves to soil compaction and we have discussed that the methods of the principle of the compaction and also the factors affecting the compaction of soils and further we will try to understand about the different field compaction methods and how the relative compaction can be assessed in the field and then some issues which are actually relevant with the influence of bulk particles on the dry densities etc in the next lecture.