 So, welcome to lecture number 9 of module 1. In the previous lecture we have introduced ourselves to soil compaction and then we discussed about the principle of compaction, factors affecting compaction and methods for determining compaction characteristics of soils in the laboratory. In this lecture we will be discussing about continuing our discussion about factors affecting compaction and field assessment of compaction and some field compaction methods. So this lecture title is soil compaction 2. As we discussed in the previous lecture especially for fine grained soils compaction it depends upon the soil structure which actually changes from dry set of optimum to wet set of optimum. If you can see from this slide here, this is for a light compaction and this is for modified compaction. So at point A the soil structure or soil fabric is highly flocculated in nature and it has high strength and higher permeability and less shrinkage and more swelling. And as we transverse from A to B it actually on the particles undergo rotation and then at point C the soil is now soil solids actually has been replaced by more water. So hence the low strength and low permeability and more shrinkage and less swelling. So this is adopted whether to compact and dry set of optimum or wet set of optimum depending upon the type of application. Because if you want to compact the soil for a subgrade then it is preferable to compact it on the dry set of optimum so that high load or high strength can be achieved. In case if we are constructing a barrier to prevent ingress of any permeant then it is advisable to compact on the wet set of optimum so that the low permeabilities can be achieved. So the scenario of in case of modified compaction also you have the similar status. So this is actually the direction of increasing dispersion is somewhere in this direction this actually happens. So what we discussed in the previous slide is that at low water contents attractive forces between clay particles predominate. So creating more or less orientation of plate like particles are trust like orientations. So at low water contents the attractive forces are actually dominating because of that more or less orientation of plate like particle results in low density. And the addition of water increases the repulsion between the particles leading them to assume more parallel orientations. So once water is added the particles are actually deprived from coming closer and so hence the repulsion of the particles takes place. If compacted wet of optimum parallel orientation is further increased leading to what is described as a dispersed structure. So that is what actually we have seen. So the soil structure has got a significant effect on the compaction. So if you wanted to test or achieve this compaction in the field then we need to have different compaction equipments. In the field basically fill soils are typically imported from a borrow site and applied to the existing grade level in layers which are called as lifts. So if you wanted to construct an embankment above the existing ground level the soil is loose soil is placed at certain water content and based on the characteristics which are actually required the soil is compacted. So these compacted layers are called as lifts. When a lift of soil is placed it will be very loose as I said and special compaction equipment is then used to compact this lift of the soil. So we have different types of soils and for these different types of equipments are required. These are rollers basically types of rollers where we have a smooth wheel rollers, vibratory rollers, pneumatic tire rollers, sheepsfoot rollers and very recently impact compactors. Rammers these are also types of for inducing dropping weight is including piling equipment and internal combustion type rammer or pneumatic type rammer. So these smooth wheel rollers basically they possess 100% coverage area under the wheel load with ground contact pressures up to 380 kPa. So smooth wheel rollers have 100% coverage area and they have a ground contact pressure up to 380 kPa. So they will be able to induce a pressure of 380 kPa on the surface of the ground so that the soil can be compacted. So in the conventional 3 wheel type the weight will be around 18 tons, tandem rollers will be about 1 to 14 tons, 3 axle tandem rollers about 12 to 18 tons. So weight can be increased by belasting the rolls with water or by a heavy sliding weight or it can be belasted with sand. So performance is affected by the load per unit width under the compaction of rolls, compaction rolls and the width and diameter of the rolls. So load per unit width and diameter control the pressure in the surface layer of the soil and dimension of the rolls affect the rate with which the pressure decrease with the depth. So these smooth wheel rollers are basically suitable for gravels, sands, hard core and hard core type soil and crushed rock and any material where crushing action is needed. So any material where crushing action is needed or crushed rock or hard core sands or gravels. Pneumatic tire rollers basically they have 80% coverage area. So 80% of area is covered by tires with tire pressure up to 700 kPa. So suitable basically for fine grained soils, closely graded sands or silty sands and best performance on cohesive soils can be obtained when moisture content is maintained 2-4% below the plastic limit. So the depth of compaction with pneumatic tire roller can be light rollers with 200 kN weight up to 150 mm, medium rollers with 50 tons or 500 kN up to 300 mm and heavy rollers with 1800 kN the depth of compaction can be ensured up to 450 mm. So these rollers which are actually shown in this slide they are basically sheep's foot rollers and we have used basically for compacting fine grained soils. The protrusions what we see here they are very effective in inducing very high pressures to the soil. So hence the kneading of the soil takes place, damping and kneading of the soil takes place when the roller rolls on the soil. So sheep's foot rollers are most suitable for fine grained soils both plastic and non plastic especially at water contents dry of optimum. So area of protrusions range from 30 to 80 cm square and 8 to 12% coverage and very high contact pressures are possible ranging up to 1400 to 7000 kPa. So because of this protrusions the area it can induce a pressure up to 1400 to 7000 kPa. As we have discussed in previous lectures in order to compact the fine grained soil a higher amount of static pressures are required to push the kilo particles closer. So the sheep's foot rollers are used basically the protrusions significance is that to induce high contact pressures. Now coming to vibrators which are basically used for sandy or gravelly soils there are two types of vibrators will be there out of balance type or pulsating hydraulic type. The out of balance type vibrator will have two eccentric masses which are actually rotated in a opposite direction which induces vibration and because of this a tamping above its centering height is created. So this makes the particles to rearrange into the denser configuration. So the vibrators consist of a vibrating unit of either the out of balance weight type or a pulsating hydraulic type mounted on a plate or roller. So the vibrators consist of a vibrating unit either the out of balance weight type what it was shown in the previous slide or a pulsating hydraulic type mounted on a plate or a roller. So vibrators give maximum dry density much in excess of corresponding compaction test value at OMC and frequencies of these rollers range from 1500 to 2500 cycles per minute. Frequency range within the natural frequency of the most of the soils so the frequencies have to be in the range of the most of the natural frequency of the soils. The another type of compaction which is known in nature is impact type compaction. It is the transfer of compactive energy into the soil by means of lifting and falling motion of a non-circular rotating mass. So in this case we have a non-circular rotating mass this actually induces an impact type of compaction energy. So it is the transfer of compaction energy into the soil by means of lifting and falling motion of non-circular rotating mass. It has been observed that this the depth of influence of compaction can be larger in case of impact compaction. So it is thus a process of capable of transferring impact load similar to those found in dynamic compaction on a continuous basis. So this is somewhat very close to the so called dynamic compaction. So the impact compaction is the transfer of compactive energy into the soil by means of lifting and falling action of a non-circular rotating mass. So as I said that the features include the energy rating of the different impact compaction equipments range from 10 kJ to 25 kJ. So the energy rating ranges from 10 kJ to 25 kJ and higher energy helps to achieve higher maximum dry density that allows to work over a wide range of moisture contents. So here it is shown here in this slide. This is with conventional compaction and this is with impact compaction. So what it can be seen is that impact compaction induces higher amount of compaction the densities are high especially this is found to be very significant when you know when we compact it on the dry side of optimum. As it has been mentioned the other feature is that increase the depth of influence. The contact stress of impacted compactor is about 300 kPa to 1200 kPa. This is exceeding the conventional rollers depending upon the soil stiffness and impact rollers profile radius is not reference to the center of the drum greatly exceeding the conventional rollers resulting in a greater contact area. So the impact rollers profile radius is not reference to the center of the drum which actually exceeds the conventional rollers and results in a greater contact area. Net result is superior depth of influence enabling the compaction in layer thicknesses exceeding more than 1 meter. So this is exceeding 1 meter. So net result is that the superior depth of influence of ensuring adequate compaction up to layer depth of 1 meter. So this is shown pictorially here. Here a conventional static pressure roller is shown here. So the depth of influence if it is D1 and with a vibratory roller if the depth of influence is D2 so D2 is greater than D1 but when you have impact energy with the impactor which is actually have non-circular compactor and because of this the dropping height which is actually you know here for this H3 will be greater than H2 greater than H1. So this means that this induces very high energy and because of this it ensures depth of influence significantly high. So impact energy of high amplitude with low frequency and because of this reason the impact compaction ensures higher depth of influences. Another feature is that increased load duration the impact compactors load duration has been measured to be approximately 10 to 15 times longer than that of conventional rollers. So this is good for some fine-grained soils to arrange into the denser configuration. So this because of this it enhances the soil to arrange into the denser configuration. So here it is shown here increased load duration for a conventional compaction if it is 0.02 seconds for a impact compaction it is about 0.12 seconds. So longer duration results in reduced soil response and greater compaction. So this is one of the other merits of impact compaction. And another feature is that high operating speeds impact compactors operate at speeds up to 5 times faster and 10 times greater volume per day than the conventional compaction equipment. So in a summary here smooth wheel rollers what we have seen here they are actually used basically for sands and gravels and pneumatic rubber tile rollers, sills and clays, ship's foot rollers basically for sills and clays and fine grained soils and vibratory rollers especially used for sandy and gravel soils and vibratory tampers also used for sands and gravels. This basically to increase the compaction energy applied to the soil in the field increase the mass or weight of the compaction equipment or decrease the lift thickness that means that if you are able to decrease the lift thickness there is a possibility that good adequate compaction can be ensured in the field and increase number of machinery passes. We also have discussed that increasing the number of machinery passes also sometimes will be wasted because further increase in number of passes does not completely ensure compaction energy. There should be an optimum number of passes. So in the field compaction as we are actually trying to assimilate in general granular soils can be compacted in thicker layers than silt and clay. So granular layers can be compacted in thicker layers than silt and clay or if you have got fine grained soils or nowadays materials like coal ash they are required to be compacted in thin layers and granular layers are usually compacted using kneading, tamping or vibratory compaction techniques and coju soils usually kneading, tamping and impact type of compaction. So this coju soils require kneading and tamping or impact type of compaction. So as per our previous discussion in the lectures we have actually classified the soils and soils such as GW, GP that is well graded gravels and poorly graded gravels and well graded silt gravel and gravelly clay and sand with well graded sand and poorly graded sand and silt sand have good compaction characteristics. So if you look into this soils such as GW, GP and GM as GC, SW, SP and SM have good compaction characteristics and other soils such as SC, CL and ML they are characterized as the good to poor characteristics as far as the compaction point of view. At any rate the quality of the field compaction needs to be assured by measuring the in-situ dry unit weight of the compacted soil at random locations. So whenever we are actually doing a compaction of a particular soil the density has to be ensured because the inadequate compaction of a soil can lead to the distress in the structure once it is released for usage. So the field compaction and specifications when it comes we actually have two categories of earthwork specifications one is that end product specification and method specifications. So we will discuss as far as the end product specifications in which a certain relative compaction or a percent compaction is specified. So here if you are actually having a coarse grained soil then we actually ensure the relative density of a particular soil. So if you wanted to have a adequate compaction we will say that 70 percent relative density or 80 percent relative density has to be achieved or when we are actually having say especially for fine grained soils the relative compaction is used. So relative compaction is nothing but a ratio of the unit weight of the soil which is actually in the field and unit weight of the soil dry unit weight of the soil which is actually obtained maximum dry unit weight of the soil in the laboratory. This maximum dry unit weight of the soil can be obtained either from the modified proctor compaction or from the light compaction test. This is depending upon the type of the specifications. This RC cannot be won because 100 percent compaction cannot be achieved. So this generally the relative compaction is defined as the ratio of the field dry unit weight to the laboratory maximum dry unit weight according to some specified standard test. For example standard proctor or modified proctor test and this is basically expressed in percentage. So difference between relative compaction and relative density if you look into it. The relative density is basically applied to granular soils and if some fines are present it is difficult to decide whether to adopt for relative compaction or relative density. According to ASTM D2049 the relative density is required to be performed if the fines that is passing 75 micron C less than 12 percent. If there are actually more than 12 percent fines then the relative compaction need to be adopted. So otherwise the compaction test should be used. So here what the relative density is basically defined as which is interrelation between maximum void ratio, minimum void ratio and institute void ratio here which is wrongly written here. The relative density is nothing but e max minus e divided by e max by e minimum into 100. So engineering properties of cohesion less soils are primarily a function of relative density dr. So in this particular slide a relationship between relative density and relative compaction is shown here. As can be seen here with void ratio infinity gamma d is equal to 0 in case of say granular soils and then e max which is at gamma d minimum, e minimum at gamma d max, institute void ratio at e is equal to gamma d. So the relative density ranges from 0 to 100. For a given project where the specifications say about 70 percent that means that at this point the institute void ratio of certain void ratio has to be achieved. In case of relative compaction it appears like it is ranges from this place to this point to this point. So this is somewhere if you are specifying say 90 percent compaction so somewhere it actually can result here. So in the field often the questions have to be answered are to what r unit weight must the soil be compacted. So what should be the dry unit weight the soil should be compacted and how can this be achieved efficiently and how this can be verified whether it has been achieved or not. So we have actually field density tests which are actually destructive as well as non-destructive tests. So for many construction applications involving roadways upgrades and trench back fills there are typical standards specifying the minimum relative compaction that must be achieved. So for many construction applications involving roadways upgrades and trench back fills there are typical standards specifying the minimum relative compaction that must be achieved. So in this particular slide a typical compaction of a soil for different projects it is shown here. Fields to support buildings or roadways minimum which is required to be ensured is 90 percent that means that 90 percent of laboratory compaction density should be achieved. Top 150 m of sub grade below roadways should have 95 percent of compaction and aggregate base material below roadways has to achieve 95 percent and in earthen dams 100 percent has to be ensured so that there will not be any seepage and distress due to settlements and all. So the relative compaction different types of relative compaction threshold limit which are required to be ensured is actually given in this slide. So here if you look into this particular slide a slide which is actually shown here the dry unit weight versus water content indicating the most efficient conditions for field compactions. So the range here if you look into this here this is the dry side of optimum that is dry to optimum and this is wet side of optimum and these are the zero air voids line and these are saturation lines which are actually having less than 100 percent saturation 90, 80, 70 like that and if you look into this here at point A and point B there is this water content is dry side of optimum and this water content is say wet side of optimum. So gamma field which is nothing but 95 percent of gamma dry max that comes out here that means that we have got two ranges of water content one is actually having dry side of optimum other is on the wet side of optimum with same density. So the range AC indicated the range of which the soil should be compacted to achieve relative compaction at any energy level. So here to achieve 95 percent relative compaction the placement water content of compacted field must be greater than water content A and less than C that means that in order to achieve 95 percent compaction the placement water content of a given soil must be greater than water content A that means that whatever is dry side of optimum let us say OMC-2 and less than OMC plus 2 let us say that point happens to be C and that is OMC plus 2 it should be less than that. So if you say that 95 percent compaction 95 percent relative compaction the placement water content of compacted field must be between these two ranges and these points are found where the 95 percent relative compaction line intersects compaction curve and if the placement water content is outside the range of A to C then it will be difficult and if not possible to achieve the required percentage of the relative compaction. That is the reason why it may be necessary at times to wet or dry the soil prior to the laying. So if the water contents are if they are not within this range it may require wetting or drying of the soil so that to ensure this so called 95 percent of the compaction. So when further when we discuss about the field compaction and specifications so having established the range of the placement water content if required to ask what is the best placement water content to use. So most efficient water content should be that OMC where the contractor provides the maximum compact effort to attain the required 95 percent relative compaction. The most efficient placement water contents exist between OMC lab and OMC field. So it must be also noted that the most efficient water content exists between OMC laboratory and OMC field. The range of placement water content should also be specified along with RC. So the compaction when we are actually doing when the borrow material has been identified when it has been characterized in the laboratory so the range of the placement water content should also be specified along with the relative compaction. That ensures that the proper compaction in the site. So in the method specifications what we have actually indicated earlier the second category the type and weight of roller and number of passes of that roller as well as the lift thicknesses are specified. So this specification requires prior knowledge of the borrow soils so as to be able to predict in advance how many passes of or for example a certain type of roller will produce adequate compaction performance. So this requires test fields before carrying out actual compaction. So method specifications is only just very large compaction projects such as earthen dams. So having discussed about the type of equipment for ensuring the field compaction and some specifications to ensure proper compaction we need to discuss about field density testing methods. First of all the question will come is that how many number of tests have to be carried out. Say for large fields about one sampling per 1000 to 2000 square meter area per lift. Per lift means per layer compacted layer and for small fields which are actually having less than 1000 meter square 2 to 3 samples per lift. And for a fill with lateral dimensions 100 by 100 meters one would expect to take 5 to 10 samples measurements per lift. So if you are having a fill by 100 meter by 100 meter size one would expect to take 5 to 10 samples per lift. So typical specifications call for a new field test every 1000 to 3000 cubic meter or so when the borrow material changes significantly. Suppose if the borrow material changes the test location should be located there otherwise a thumb rule is that 1000 to 3000 cubic meter of soil a new field test has to be carried out. So the field density tests are basically two types one is destructive test other one is non-destructive test. Distractive method involves excavation and removal of some of the fill material whereas non-destructive test determine density and water content of the fill indirectly without destroying the compacted layer. Destructive methods are basically divided into two methods one is sand replacement method and core cutter method other one is rubber balloon method where if you have got improper soil profile then the rubber balloon method can be used particularly if you are assessing unit weight of municipal soil waste deposit the rubber balloon methods are very very useful. Non-destructive methods include the nuclear density methods which we will be discussing in further slides. Destructive methods are time consuming and each and every location the layer has to be disturbed and also it requires determination of water content so that the dry density or dry unit weight can be determined. Nuclear density method has high purchase cost and the safety precautions during the nuclear density test method have to be followed. The safety precautions during nuclear density tests have to be followed. The sand replacement method or sand cone method which is nothing but a sand with known density is filled in the sand cone jar and weight of the sand cone apparatus along with the sand which is recorded. So here for a certain type of standard sand need to be used and if that weight of sand cone apparatus with sand is say W1 and weight of the sand to fill the cone is to be determined is W2 so that is for the weight of the sand to fill the cone is said W2 and if the sand hole in the compacted soil is excavated and weighed if suppose if the small hole in the compacted soil is say excavated and weighed. So if you wanted to determine in particular layer so what you will do is that we will excavate a small hole and weigh the soil and that weight is say W3 the apparatus is inverted over the hole and valve is opened. So we will release the sand into the portion where the soil has been removed compacted soil has been removed. So weight of the apparatus with remaining sand is determined and that is W4. So once we if you can get weight of the sand to fill the hole if you are able to get that can be obtained by W1 minus W2 plus W4 within brackets and the volume of the hole can be obtained as weight of the sand divided by gamma d sand. So weight of the dry soil can be obtained by W3 which what we actually obtained by removing the particular soil from the portion what it is shown here and divided by 1 plus W will get the dry weight of the soil and the dry unit weight can be obtained as Wd divided by volume V. See volume V is nothing but volume of the hole is nothing but the dry sand unit weight will be knowing and Ws that is the weight of the sand. So once I know this that is weight of the sand to fill the hole divided by this I will get the volume of the hole. So with that dry unit weight Wd by V can be determined. So in majority of the cases we have situations where the relative compaction of the fill containing over size particles comes into the picture. So sometimes this needs to be corrected otherwise the field densities measured can be misleading. So over size particles will be defined here as the rock that is retained on 19 mm sieve the soil matrix is the material passing 19 mm sieve. So if you are having a fraction which is actually say passing retained in 19 mm sieve and that is actually called as fraction of the over size particles. So there are 3 methods we will be discussing one method that is elimination method. So these 3 methods are elimination method adjustable maximum dry unit weight method this is according to dm 7.2 and this is suitable when the weight of the over size particles is less than 60% by weight and substitution method. Out of these 2 with an increase in this over size particle fraction the elimination method the total densities predicted by elimination method will be on the higher side. Both adjustable maximum dry unit weight method and substitution method they are close enough to you know account for the corrections which are actually possible because of the presence of the over size particles. So this elimination method involves that perform the field density test and determine the total volume and total weight of the soil. Depending on 19 mm sieve separates the over size particles from the soil matrix with that we know that weight of the that is the gravel fraction. So knowing the weight and specific gravity of the over size particles the volume of the over size material can be calculated. So assuming that a field that must be compacted to 90% relative compaction so use of the elimination method would require the highest field density values. So this implies that assuming a field that must be compacted to 90% relative compaction the use of elimination method would require the highest field lower dry density values. So here in this slide according to day 1989 the 3 methods which have been cited here have been discussed by day 1989 the relationship between the total dry unit weight of the field to the fraction of the over size particles is given here. Gamma total is the total weight of the soil matrix and gamma d max is the maximum dry unit weight of the soil in the laboratory, rc is the relative compaction, gamma w is unit weight of water and gamma w is unit weight of water again, g0 is nothing but the specific gravity of the over size particles and f is nothing but the gravel fraction and gamma d max is again the laboratory dry compaction value maximum dry unit weight of the soil. So the total is given by gamma d max rc gamma w g0 into 1-f plus f into gamma d max into rc. So if you substitute for a given type of soil with certain characteristics of over size particles it will show that as the fraction of over size particles increases gamma total increases this is because the more over size particles in a field then the higher gamma total must be in order to keep the soil matrix at a desired relative compaction. So by using this particular expression and the discussion it is possible to account for the presence of over size particles in the soil matrix and this needs to be considered if we are having the particles which are actually more than 19 mm or retained in the 19 mm in the while testing field density method by using sand density that is sand cone method. The next method which we have said is the nuclear density method this uses a low level radioactive waste source that is inserted via probe into the central center of a newly compacted soil layer. So this is one type of method in which a small trench is made and a low level radioactive waste source is inserted but there are also some sources where the nuclear density measuring apparatus will be on the surface of the soil in touch with the soil and then it also will measure the source basically emits rays through the compacted soil that are captured by a sensor at the bottom surface of the nuclear density device. So the intensity of the captured radioactivity is inversely proportional to the soil density the intensity of the captured radioactivity is inversely proportional to soil density. So this apparatus is calibrated using sand cone replacement method sand cone or sand replacement method for various soils and it is usually provides reliable estimates of for moisture content and dry weight. So this needs to be calibrated by using you know conventional method once this is calibrated then this particular method can be used very rapidly to get the densities and water contents achieved after the compaction. So this method provides fast results allowing the user to perform a large number of tests in a short time and also enables to release the layer for a next lift compaction immediately. See the nuclear moisture density methods the principle elements include nuclear source emitting the gamma rays and detecting to pick gamma rays passing through there is a detector which picks the gamma rays passing through the soil and counter to determine the rate of gamma rays reaches the detector. So it actually has got two three fundamental elements once one is that emitting gamma rays other one is a detector other one is the counter. So common nuclear sources are radium-beryllium combination and cesium-americium and beryllium combination. So these are the common nuclear sources which are actually used in nuclear moisture density methods. So density determination the principle involved is like this gamma rays penetrate into the soil and some are absorbed and some reach the detector. Amount of radiation reached is reaching detector is inversely proportional to the soil and basically soil density and nuclear count rate received at the detector compared with the calibration curves provided by the manufacturer. So nuclear count rate received at the detector should you have to be compared with the calibration curves provided by the manufacturer. Similarly for the moisture determination moisture content is obtained from the thermal neutron count alpha particles are basically emitted by the source, americium or radium source which bombard a beryllium target emitting fast neutrons. The fast neutrons lose velocity if they strike hydrogen atoms in water molecules. So resulting low velocity neutrons are called as thermal neutrons. So based on this the estimation of water content is done through in the nuclear density methods. So moisture results are provided as a weight of water per unit volume of soil tested and dry weight is obtained from the subtracting the moisture determination from the wet density determination. So significant error occurs in soil contents iron, boron or cadmium. So there is a possibility that one of the limitations is that a significant error can occur if the soil being compacted or compacted contains iron, boron or cadmium elements. The first method is actually shown here provides more accurate results and radiation sources are placed into the test material by using puncture or drill hole and depth between 50 mm to 300 mm can be tested and information surrounding the source is obtained. So this is shown picture really here. This is the trench which is actually placed and it actually emits the gamma rays and then is gamma of proton detectors are here and this is the nuclear gauge which is actually in touch with the soil. In case of second method backscatter method it is called radioactive source and detector located on the surface of the soil itself. This is actually widely used in majority of the equipments available and gamma rays directed into the soil and some reflect back to the detector and accuracy suffers if there is a gap exist between the soil surface and the nuclear density device. So information about the soil nearest to the surface is actually obtained. So in this method in the backscatter method where you have got the detector and this source they are actually at the same place and it has to be in touch with the soil and it is possible that information from the surface of the soil can be obtained very effectively. The third method is the air gap method which is basically a less common method and is used when the composition of the near surface materials adversely affects the density measures then a stand is provided and the density is measured on the surface. So this as I said that the soil is compacted in different lifts and if the lift thicknesses are too large then the following can occur. Soil at the top of the field will be well compacted and soil at the bottom of the lift will not be compacted at all. So if I have a lift thickness of say more than half a meter then soil at the top of the lift appear to be compacted and that can give the misleading results and then overall what will happen is that when we have got the number of layers which are compacted like that this can lead to the distress and leasing to the performance and serviceability of the structure which is being used for a particular application. So soil at the top of the lift will be well compacted and soil at the bottom of the lift will not be compacted at all. So here in this slide a particular lift layer thickness if it is there you can see that the soil at the middle portion is compacted very well at the interface point there is a possibility that the compaction is not achieved at all. So it has to be ensured that the lift thickness should be such that the minimum compaction is actually met at all points. So that if this is the 95% compaction which is actually required then this particular zone is actually shows that the lift thickness is such that this is actually has inadequate compaction but if you have a lift thickness such that there are the 95% compaction is achieved then this is actually preferred here. This is with adequate compaction and this is with inadequate compaction. And here in this particular slide field dry density versus number of passes is shown. So the dry density versus number of passes and if you have got a wetter soil the number of passes will not actually help because as I said here the pore water pressure which actually increases and will not allow the soil to compact. And similarly with the natural soil with increasing some in case of dry soils the increasing number of passes can be somewhat appear to be effective here may not be initially but with higher number of layers for the drier soils there can be higher densities can be achieved. So here at one moisture content with different thicknesses it can be shown here. So the dry density achieved with the number of passes you can see that with the increased number of increased layer thickness the density achieved for a given number of passes is less. But increasing number of passes with more number of passes is not having particular influence. And mostly for compaction equipment the lift thickness should be typically be out of 150 mm or 300 mm. So in that case what will happen is that the wheel of the compaction element like a pressure bulb it actually has got high stress region as well as the low stress region. So if this is ensured this possibility that the compaction can be effectively can be ensured in the field. So the approach method for determining the lift height in the field is according to de-Aplonia 1969 is that first for a given for a large lift height you with a particular number of passes determine the relative density with depth. So if you have if it is achieved for a largest lift height say D max so the density depth relationship for the large lift height using 5 roller passes if the depth used to be D max that D should be small enough so that the loose layer is not trapped near the interface between the left. So this particular D should be small enough so that the loose layer is not trapped between the two compacted layers. So this is one layer lift compaction this is another layer lift compaction and we have to ensure that as it was shown in the previous slide that this particular point is actually well above the desired relative density or desired degree of relative compaction. So in this particular problem, particular slide we will see a problem on the compaction the given data is that water content versus dry unit weight and we need to plot the compaction curve and the water content data and the unit weights are given and we need to plot 80% and dry 100% saturation lines that is part A, part B is that if it is proposed to secure a relative compaction of 95% in the soil what is the range of water content that can be allowed and would the 20% air voids curve be same as the 80% saturation curve. So we have discussed in the previous lecture that they are not same but let us see how that can be illustrated with help of this problem. So based on the given data if the graph is actually plotted with dry unit weight on the y axis in kilo Newton per meter cube and water content on the x axis then this is the compaction curve. By using this gamma d is equal to gs gamma w plus 1wg 1 plus wg sr by sr we can actually determine the 100% saturation line so the gamma d max is equal to 17.45 that is this density this dry unit weight and water content optimum moisture content of 15.17%. So this particular data for a given soil which has got the maximum dry unit weight of 17.45 kilo Newton per meter cube and optimum moisture content of 15.17% and this is 100% saturation line and this is 80% saturation line. Now in continuation of to determine the relative compaction with 95% relative compaction is specified so gamma d field which is actually required is that 0.95 into 17.45 is 16.58 kilo Newton per meter cube. So range of water content that can be allowed in the field is 10 to 17% that is from this slide for that particular density 95% of this the range of water contents can be allowed in the field is ranges from here to here that is now the discussion about 20% air voids curve and 80% saturation line whether they are same or not. So we knew that 20% air voids line means we can actually compute gamma d is equal to gs gamma w into 1 minus na, na is nothing but the percentage air voids plus 1 plus wgs and this yields for na is equal to 0.2 that is 20% air voids and at water content of 8.5% the gamma d has 17.22 kilo Newton per meter cube which is actually found to be different if you try to compute for 80% degree saturation gamma d is equal to gs into gamma w plus 1 plus wgs by sr when sr is equal to 0.8 and water content is equal to that is 8.5%. The density which is actually obtained is around 20.56. So this density is actually different from what is actually obtained from this one. So if they are have to be same then we need to actually get the same values hence we can say that the 20% air voids line which is actually air voids curve is not the same as the 80% saturation lines similarly air content lines also. So these are all methods what we discussed is about the shallow compaction methods but there are situations where we have got requirement to compact the soil at deeper depths and for that there are a number of techniques which are actually available traditionally the terra probe method which was available and now currently the one which is actually being used is vibro flotation and building sand compaction piles blasting and dynamic compaction and these are actually covered in detail in ground improvement subject but in place densification of granular soils is very much required nowadays if you are building a structures which are resting on saturated sandy or silty sandy soils and this too as a remedial measure for preventing liquefaction susceptibility in the future. So they have been successfully used for compaction in suited soils especially granular soils. So in this slide the terra probe method which is actually shown here and works best for shallow water tables and it actually has got activated vibro driver causes the probe to vibrate in the vertical direction the probe actually vibrates in vertical direction and to achieve soil compaction the probe is actually vibrated to the planned depth of the penetration. So the spacing is generally 1.5 meter which is actually placed and the area is actually compacted. So here this particular photograph shows the process of compaction by using the terra probe method. In the in place densification of granular soils that is for vibro flotation when conventional rolling type compaction equipment works the surface of the area the improvement in the density is limited to the only 1 or 2 meters. But if you have a requirement of compaction at the deeper depths then these institute densification which is actually required to be adopted up to certain depths means then vibro flotation is a viable option. So vibro flotation equipment operates from sites at ground surface but it can densify the full depth of the granular deposit which are deep as about 12, 14, 15 meters. So up to 15 meters the vibro flotation equipment generally can be used for densifying the soil even at deeper depths now it is being tried and the ranges of the soils or particle size distribution which are actually possible for an option is here particularly the range of the particle size distribution suitable for the densification by vibro flotation which actually shows that the soil should be gravel or sandy if they are in the loose state then it is possible that they can be compacted. But you can see here when it comes to clay the usage of this method is actually limited then we have to adopt appropriate methods. The vibro flotation method involves using a device called vibro floto vibro float which is a cylindrical piece of equipment about 2 meters long, 4 and a moment diameter and weighing about 17.8 kN. So what it does is the vibro float this exerts vibrations in vertical as well as the lateral directions. This makes the soil particles to arrange into the denser configuration. The eccentric weight inside the cylinder develops a centrifugal force of about 89 kN at 1800 rpm. The device has water jets at top and bottom so these water jets actually will allow to the probe to penetrate at a rapid rate and the flow rate is about 0.23 to 0.3 meter cube per minute at a pressure of about 415 to 550 kN per meter square. That means about 4 to 5 bar pressure the device can actually operate and jet the water. So with that what will happen is that the penetration of the probe takes place very easily and the vibro float sinks into the ground at the rate of 1 to 2 meter per minute when the desired depth is reached the top jet is turned off and the device is done withdrawn at the rate of receding rate is about 0.3 meter per minute. So the sinking rate is about 1 meter to 2 meter per minute and the withdrawal rate is about 0.3 meter per minute and the sand is actually added from the top and if you are actually adding other materials then it is called as vibro replacement. So in a regular working day a compaction of 2550 to 5100 meter cube is not uncommon by using this method. So the process is actually shown here pictorially the jetting of the water and then the compaction and then withdrawal here. So here in this process what will happen is that the deeper soils can be compacted and when you do it at certain grid of spacing covering the large area then entire soil needs gets densified. So here at start lower jet is opened fully and here at the portion this slide 2 water is introduced more rapidly than it can drain away. So this creates a momentarily the so called quick condition ahead of the equipment which actually permits the vibrating machine to settle its own weight. So the weight itself is actually sufficient to settle the probe up to the desired depth. Once in the third step the water from the lower jet is actually transferred to the top jets and the pressure and the volume are reduced just enough to carry the sand to the bottom of the hole. So with that what will happen is that and again the sand which is actually introduced there is compacted by using the vibro float which is actually available at the surface. So this process actually makes a replacement of the loose soil with a densified column or a densified column actually having a densified sand. So actual compaction takes place during intervals between 0.3 meter lifts which are actually made in return with the vibro float to the surface. So this is how the process of the vibro floatation is actually done. There are other technique which is called as the blasting. So this generally is adopted when you are actually having top layer also a loose soil. Suppose if you are having a this blasting is nothing but the arranging creating a soil the soil densification by supplying a explosive energy. The range of soil grain sizes suitable for compacting by blasting method are same as the vibro floatation. In this method the compaction is achieved by successful detonations of small explosive charges in saturated soils relative densities up to 70 to 80 percent up to depth of 20 to 25 meters can be achieved. But one important caution is that if you are having a dense sand layer on the top and loose sand layer at the base then in such situations this particular technique need to be avoided because it can lead to the loosening of the top sand layer in the process of compacting the loose sand layer beneath the dense sand layer. So these are the in the explosive charges are basically 60 percent of dynamite 30 percent special gelatin and ammonia are most commonly used and they are placed generally about the two-third times the thickness of the stratum and the spacing generally vary from 3 to 8 meters and there are five to successive detonations are placed so that the soil can be arranged into the dense configuration. So the shockwakes actually create a sort of liquefaction and make the soil compacted into desert configuration. So this is a particular relationship which gives weight of charge to a sphere of influence of that energy W is equal to C R cube and R is nothing but the sphere of influence and C is nothing but the material constant that is 0.0025 for 60 percent dynamite. So the last method what we have actually said is the dynamic compaction which is nothing but the dropping of a known weight from a known height which actually creates a sort of primary waves and secondary waves and this is actually when it is done in a soil it creates the so-called rearrangement of the soil particles and makes the soil particles displaces to the denser configuration. So this method consisting of dropping of a weight from a relatively greater height so the weights ranging from 2 tons to 15 tons and drops having range from 10 to 13 meters have to be adopted. So usually the close spacing pattern of like 6 meter by 6 meter is called as a print spacing need to be adopted and each we have primary pass, secondary pass or tertiary pass. This can densify loose dense cohesionless soils and fracture and densify buried building rubble and nowadays old building sites or construction debris or some waste landfills are also being compacted by using this method. So in this lecture what we have actually introduced is that field compaction testing methods, their assessment of the field compaction of the field and then we also discussed about how we can actually correct in case if we are having a over size particles and then in addition to the shallow compaction methods what we discussed. We also have discussed about an introduction we have given to different methods which are actually existing for densifying the soils at greater depths. This is required for strengthening the soils against liquefaction susceptibility.