 This is Dr. Mahesh Kallanshatti, Associate Professor, Department of Civil Engineering, Valchan Institute of Technology, Solapur. In this session, we will discuss about determination of consistency limits. The learning outcome of this session will be, at the end of this session, students will be able to perform the test in the laboratory to evaluate consistency limits of soil. Let us take a review of the Atterberg limits, which has been already discussed in the earlier presentation. So, with the help of this particular figure, we can define the various limits which are been proposed by Atterberg. First one is the liquid limit, then this is a boundary motion content between liquid limit, liquid state and plastic state. Then the plastic limit, this is a boundary motion content between the plastic state and semi-solid state. And last one is the shrinkage limit, which is the boundary motion content between semi-solid state and solid state. Now, we will focus on determination of these Atterberg limits. Atterberg original consistency limit tests were rather arbitrary and not easily reproducible. So, these consistency limits are very arbitrarily set by Atterberg and these are not easily reproducible. So, therefore, one scientist called A. Kasegrande subsequently standardized the apparatus and the procedure to make the measurement more repeatable. So, he is A. Kasegrande. So, you can have a more detail of this scientist referring this particular link which is given. So, Kasegrande has developed the apparatus which are used to find the Atterberg limits. First of all, let us see the determination of liquid limit. This is also called as Kasegrande's mechanical method. The water content required to close a distance of half inch that is 12.7 mm along the bottom of the groove after 25 blows is defined as a liquid limit. Of course, this definition is related to the apparatus which is been developed by Kasegrande. So, let us have a look at these apparatus. Now, this is called as Kasegrande's apparatus. So, which basically consists one brass cup which is been mounted on a hard rubber pad. So, you can see here this is a hard rubber pad and there is a handle attached to this. So, the arrangement is made in such a way that when you rotate the handle, this brass cup is raised by 1 centimeter and it is allowed to fall on a hard rubber pad which creates the impact. So, in this way if you do one rotation here, there will be one blow given to this particular cup and all the details of this particular instrument are given here in this case all the dimensions you can see here. So, what we are supposed to do is first of all you have to take a fine grained soil passing 425 micron and you have to add some water in it and prepare a paste of the soil. That paste of the soil is to be filled in this cup as you can see here. After filling in this cup, we have to make a groove inside with the help of a grooving tool. So, this is a typical grooving tool which is shown here. This is another view of that grooving tool with some standard dimensions that is available in the laboratory. So, with the help of this grooving tool, you can see it at the edge or at the end we have a gap of 2 mm. So, with the help of this grooving tool, the separation is made here so that we can see a groove of almost 2 mm width and once the groove is made then we have to give the blows to this particular cup with the help of this handle. So, we have to rotate the handles so that this cup is being raised and it is allowed to drop on the hard rubber pad which creates an impact. Further, once this process is over then what we are supposed to calculate is so here if you look at this definition the water content required to close the distance of 12.7 mm after giving 25 blows. So, we have to find out the water content of the soil at which if 25 blows are given then the separation closes by 12.7 mm. So, it is very difficult to find it at the first trial. So, therefore, as it is mentioned here it is difficult to adjust the moisture content in soil to meet the required 12.7 mm closure of the groove at 25 blows. Hence, at least four tests for the same soil are made at varying water content and then water content values are plotted against the logarithmic of the number of blows. So, this is an procedure which you adopt in the laboratory. So, what we do here we take minimum four trials of different water content. For example, if I go for first trial then if suppose after giving say for example almost say 30 to 35 blows if the separation closes by 12.7 mm then that point I will plot here. So, this is the first trial. Then we will go for a second trial wherein we add little amount of water in that soil and again we will perform the same test and naturally in the next trial as the water content is increased number of blows will get reduced. So, suppose the number of blows reduced here it is around 27 and water content naturally will be more than the previous trial. So, this is the second point obtained after the second trial. In the third way we go for a third trial which increased in the water content. We may go for fourth trial again with increase in the water content and in this way we obtained four points here and we have to join these particular points by a straight line which gives you a flow curve. This line is called as a flow curve and once we obtain this particular line then we can find out the liquid limit. As we know the liquid limit is nothing but it's a water content at which 25 blows are required. So, at 25 blows we can just find out what is the corresponding water content. So, that works out to be near about 42. So, in this way we can say that the liquid limit of this soil is 42 percent. So, this is how we perform the test in the laboratory with the help of that Casagrande's apparatus and we need to take minimum four trials so that we can obtain this particular line and one more thing here on x axis the number of blows are plotted on a log scale. Therefore, it is called as a semi log plot. Now, naturally this particular number of blows may vary from one blow up to even 100 or 200 blows also and all the blows very accurately we want to reproduce here and also the length of the axis would have been very large. Therefore, to reduce the length of the axis and at the same time we don't want to compromise on the accuracy. Therefore, it is suggested to plot it on a log scale. Therefore, it is a semi log plot to find the liquid limit. For the second limit is a plastic limit. Now, this also is a laboratory process and trial and error is required. So, it is called rolling into thread method. So, the plastic limit is defined as a moisture content in percent at which the soil crumble when rolled into a thread of 3.18 mm in diameter. So, again you can do this thing. So, we take a small ball and then this ball we have to gently turn into a thread. So, we have to roll your finger on this ball and slowly turn this ball to a thread and continue this process till the crumble the thread starts crumbling. So, the crumbling should start exactly at around 3.18 mm. So, this also is very difficult now because we don't know at what water content exactly the crumbling starts at 3.18 mm. So, we have to go for number of trials and the trial at which we observe that the thread starts crumbling at 3.18 mm then that water content of the soil we call as plastic limit. So, this is again a trial and error method. The third one is shrinkage limit. Now, in the shrinkage limit with continuing loss of moisture a stage of equilibrium is reached at which more loss of moisture will result in no further volume change. So, as in the first slide itself we have seen that the shrinkage limit is nothing but its water content at which reduction of the volume of the soil stops almost. So, that water content we need to calculate. The shrinkage limit is defined as the moisture content in percent at which the volume of the soil mass ceases to change. So, this is how we can find it. For example, now if we can see here the volume goes on reducing here and we come across with one water content at which the volume reduction stops and further it remains constant. So, this water content is nothing but the shrinkage limit. So, let us consider a soil sample at one particular limit here say having a water content of say W1 and then as the water content is reduced the volume also goes on reducing and it ceases here. So, the shrinkage limit is nothing but its initial water content minus the loss of water content from this point to this point. Therefore, here you can see in this equation initial water content minus the delta W means the loss of water content from this point to this point. Now, again this is the state of the soil at this particular limit at the initial stage and this is the state of the soil at the shrinkage limit. You can see here at the shrinkage limit the soil volume has reduced and if I call M1 and V1 that is mass and volume of the soil at the first trial and M2 and V2 or VF is the volume and mass of the soil at the final stage. So, the initial water content is nothing but M1 minus M2 upon M2 that means the weight of water upon weight of dry soil into 100 and the change in water content is given by V1 minus V2 VF of course upon M2 into unit weight of water. So, here from these two diagrams this equation we can derive to find the change in water content. So, in this way this using this equation I can find out the shrinkage limit. So, let us take a review question and answer it and then you can resume to the video. This is the first question, this is the second question, this is the third question. Welcome back, hope you have come up with the answers. So, the plastic limit of soil is the water content at which the soil crumbles when rolled into a thread of diameter 3.18 mm is the correct answer. This is the second question, this is the correct answer, third question and this is the correct answer. These are the references which are used for the presentation. Thank you.