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Video 1: Field and Zero Tension Lysimeter
So, as I said lysimeter is a pore solution collection device and there are two varietiesof this zero tension lysimeter which is collecting the pore solutions from the saturated soils.One of the ways could be used saturate the soil sample and then squeeze or do a consolidationtest.So, one good example to the question that you are asking or the answer to the questionthat you are asking would be, I will saturate the soil sample and I will compress it ina regular consolidation ring and I will make arrangements so that the rather than, youknow, keeping the water inside the ring, I will allow the pore solutions to come outso, I can dissipate the pore water pressures.And the pore solution which comes out would be nothing but the pore solution from thesaturation soils.This is a simple device which you can device all that you have to be careful about thechemical activities and its reaction with the tubings and the oedometer material whichyou are using and you have to be very careful, otherwise, the chances are that you will becontaminating the pore solution externally.So, most of these studies require clean rooms, you have to maintain utmost cleanliness andyou have to eliminate the chances of external contamination of the sample.And these type of labs do not look like conventional geotechnical engineering laboratories.So, they are clinical laboratories where you do clinical examination and where these typeof studies are becoming more important right now is when somebody hires you to, you know,to help the industry or the organization to fight a legal case.These type of cases are becoming very, very routine nowadays, allegations or violationof the environmental norms where you could be under severe threat including the imprisonment.I hope you are aware of this type of norms, which are prevailing under the environmentalacts of the republic's and the countries.So, this is a simple model I hope this explains to you what the lysimeters would look like.You know, there is a control volume which has to be created, this control volume couldbe stainless steel, this could be aluminum this could be perspex or inside the ground,this could be the soil mass itself.And they are what we normally do is we excavate.This much soil and we fill up this space with the pervious fell.And the pervious was could be the sands or it could be the gravels or it could be themixture of both of geotextile depending upon what type of precision you require, and thenat the bottom of this there is a drain which is taken out and once I do artificial rainfall.So, this could be done in the field also this could be done in the laboratory also you cando artificial rainfall,You can sprinkle water sometime you can waterlog this whole sample by flooding it and thenas an when percolation takes place, this soil that you have recompacted becomes saturatedand the percolation occurs all the pore solution gets accumulated into the pervious fills,and then you can drain it out from here to a collection bottle.And this collection bottle is similar to the one which normally nurses use for storingyour blood sample.We call them as vials they also call them as vials.So analogy is simple.I am sure you must have realized that the though It appears to be a very simple device,but this can answer a lot of questions which we ask first of all, we can study what thesoil is doing over there, you know, we can also find out the hydraulic conductivity.So, there are papers which have been published by my ex-students, you should refer to wherewe have determined the unsaturated hydraulic conductivity of soils.Sneha Kurian and Hanumantha Rao and all these papers you should be going through to realizethat how the lysimeters can be utilized to obtain unsaturated hydraulic conductivityfine and here I can do some more experiments, if this water which I am using for artificialrainfall, I can contaminate it with some chemical species and then I can see what type of percolationis taking place and what type of percolents are getting deposited in the you know, perviousfill.So, this is what is going to tell me how much is the sorption capacity of the soil underin-situ conditions what is the attenuation can the properties of the materials and henceI can use lysimeter for characterizing the soil must also allright.So, this is one of the ways of taking all the pore solution is this part clear of coursethis process is very time consuming.So, what I can do, I can make a small miniature setup and I can install it in the centrifugeand I can accelerate the seepage process by n square times is it not?So, this type of tricks people are going to take out the pore solutions.There is another interesting example of how the field lysimeter looks like.So, in this case, you take out the sample in the undisturbed from the field and youcan place it over here alright.And then, you know, we cover it with the gravels on all the sides and what happens is the percolatingwater which is passing through this and then some mechanism by which we have connectedthe gravels to the outside environment in the form of wells.And from here I can I can put a electric electrically operated pump which will pump out the poresolutions which can be collected in the leachate.So, this there are different designs of the lysimeter.The whole idea is that you create a system which is having high permeability and packeton the top of the on the on the below the soil mass.However, as you are aware the limitations of the falling head test and the constanthead tests are that there could be percolations from the contact between the surfaces of thegeomaterials which you have used and the lysimeter itself.So, this is not a very good way of studying the lysimetric behavior of the geomaterialsand of course, fines may get washed out.So, when we talk about the collides and the contaminant mobility that has to be studiedinto this.Similarly another problem is that organic matters might react with the water.And that might also get altered because of prolonged interaction with the water.Then you will find this type of zero tension lysimeter also in the literature do not drawthem.These are all available on the net you can see them and as I said, these are all prehistoricnowadays, such as images are not being used.I wish to show you a very state of the art lysimeter.And you will be surprised to know that the cost of that the lysimeters run in few crorestens of crores, so Germans are the best in the world in designing the lysimeters.So sometimes when you get time, please visit Germany and See how lesimeters have been installedfor different projects.alright.So this is something interesting worth seen, you check it on net and you will find thatthere are some German companies who are selling lysimeter.So you just type the word lysimeters and German companies and you can see its unimaginable,there will be a big hall like this inside people sit and observe what is happening inthe fields or in the on the in the project on the project site.So, this appears to be a very complicated type of a system what has been done is thatyou have to install a sand layer and then there is a sloping bottom.So that whatever percolation takes place from the undisturbed soil core passes to the sandgets collected over here and the air inlet which has been provided, and there is an outletwhich has been provided.So these type of systems are very complicated.Design under field condition, but yes these are these are design and use some once upona time.

Video 2: Collection Basin Lysimeter
There is a simple example of what collection basin lysimeters are undisturbed or unsaturatedwithout altering the density no gamma d remains constant.Why gamma d should change gamma d then plus we would not be getting the exact concentrationof the contaminants that are present right.So, one thing is when we are like adding external water, external water contaminant let us sayin that case the sample is getting disturbed right how in the form of concentration ofthe contaminants how much how much will be the static pressure even for one meter watercolumn on the soil sample which is exerting.How do you do falling head test.So, did you ever take the effect of one meter height of the water which is standing in thetube?So falling it is also you have done on a compacted sample.So, once you have done the compaction you have already created a state of the materialcorresponding to a density and the void ratio.Now, this density and the void ratio cannot be altered by one meter water column unlessyou apply very high pressures on this alright.So, your question is correct as long as the percolent is not pressurized, I do not speculateany changes in the soil samples and the logic is this because I have already compacted itclear.Fine.Sir, lysimeter, when we are leaching through leaching we are obtaining the solution,then the concentrations will be altered only the constituent like we will be getting sobasically your question is about how to maintain the concentration of the contaminant, in yourconsolation also you talk about different types of stresses different combination ofstresses different types of training conditions, one side close one side draining one sidepartially draining another side partially closed.So, many conditions I can create is it not?Are you getting this point?So, I can create a C not condition which could be variable with time also, which will remainconservative time also clear by maintaining very high concentration of the fluid.So, delta C is going to be extremely low I can do all sorts of technical manipulations.Yes sir can we check the chemical attenuation potential of the contaminant even soil bythis chemical attenuation potential.Sorry.Yeah, of course.So, sometime after today's lecture and when we will be discussing about sorption desorptiontechnics we will be using a quantified term there R retardation coefficient and that Ris basically attenuation coefficient of the material, by this method by this method.Yes, yes, yes, exactly, that is the whole fun.So, now you are into the thick of it and now you are talking about the philosophy and thenlater on comes the quantification of the process will do everything.So, this is a collection based in lysimeter and normally this is designed for checkingthe vulnerability of the clay liners which are using the landfills vulnerability againstwhat number one is percolation of water, number two against percolation of contaminants.Third, what else it could be temperatures you see we have discussed so much that theliners which we are placing at the bottom of the landfills might get exposed to hightemperature gradients, why?Because of the chemical reactions which are going on inside the landfills.So, these are the barriers which might also act as a thermal barrier under any circumstancessorry under no circumstances the clay liner should crack either because of chemical reactivityor because of physical damages when you are laying and compacting or because of swellingshrinking or because of chemical reactivity or because of extremely high temperaturesand so on.Fine.So, here what we do is we put a clay liner on the top of a granular backfill and we placea perforated pipe at the bottom.And why this is known as collection this and because, you are creating a V sort of a system.So, the percolants will get collected at the bottom most point which is triangular, andfrom here, which is perforated pipe system, you can suck out all the leachates.These type of mechanisms or systems are normally prevailing and provided in landfills.So, when you see the landfill design this type of Clay liners are designed.Now, what I can do is I can expose this whole thing to the rains artificial rains.Let the water percolate through it and then I can find out what is the permeability ofthe clay liner under you know, in situ conditions and what type of contaminants are going topass through it as a function of time all that manipulation can so, as and when thepore solution comes, those are the properties corresponding to time.So, leachate characteristics after filtration would depend on the time of interaction also.Fluids with different viscosity will travel with different rates.Excellent.So, If we going to create artificial rains.Is there a chance that the water we supply is going to be collected before the contaminants?Yeah, you are right.So, yes, there could be a chance that has to be mathematical modeled.So, imagine if this was a confinement if this was kept in a confinement whole thing.And if I allowed a rainwater to get accumulated over here, so concentration, are you tryingto say that the concentration is slowly building up?That is what your concern is, it is not about the concentration even before the contaminantsstart to flow.Let us say let us say this boundary alright, is water capable to come even faster thanthe contaminants?No, but contaminants are in the liquid form.So they are dissolved in the water itself.Water is the carrier?So your point is correct.So these contaminants are dissolved in water and you That solution is percolating throughit or it could be reversed way, if I want to see what is the level of contaminationof this clay liner, I will be washing it through with the more purest form of the water clearand then let me see what gets percolated.So, this is not a washing experiment decontamination desorption experiment and then I would liketo study how much the soil would like to retain into it clear an agricultural scientists willbe very happy to do these type of experiment in the lysimeter why because he is going togrow a crop and he wants to see even if the extreme flooding occurs, what are the chancesthat this soil will retain nutrition into it even after let us have one year of floodingof the entire system.See I have changed the context of the problem, now.But, yes this is what agriculture scientists would like to study.So, this is where you require very high new attenuation capacity of the soil is also clearso very high sorption rates is good, very high disruption could also be good for somethingelse for another situation is this what you are asking?So, the thing was, I was assuming the contaminants to be fluid form and water and the contaminantsare going to be having different viscosity contaminants are mostly heavy metals, mostlybecause you are interested in knowing how heavy metals would leach and cause what typeof havoc to the porous media.Clear?So, either you can take the leachates which are coming out of the landfills and you canpull them over here and you can simulate a condition what type of clay linear shouldbe designed at what porosity made up of what soil made up, how much depth thickness allthese things.So, it depends upon what you want to do.So, I can use pure water I can use contaminated water this is what is known as artificiallycreated contaminants.So, if you understand that these are the heavy metals for which you want to see the responseor the clay liner, I will use that particular species of the contaminant in the water dissolveit and make a solution and let it pass through it or I can create a competitive you knowcontaminant migration also.So, I will have different species of contaminants in the solution form multi contaminant systemI may create and then I would like to see which contaminant is coming faster.So, and which has higher sorption capacity on the soils.So, all these things can be done this is the bigger picture of the whole studies.Sir, what is the efficiency of collection of this porous solution, what is the efficiency?How can we make sure that the entire pore solution is getting how the entire pore solutionis getting collected where in this you know, this is a sloping area, is it not?So nothing would stand as it is somewhere here or the whole idea of making a slopingground is that whatever is percolating will come and get collected over here, whateveris percolating is collected.But how can we make sure that nothing was getting percolated, I need not to wait forthat, because most of the time, you know how the sampling is done, you may do samplingwith respect to time or with respect to special distances, alright.So, I will do maybe 10 times sampling for 10 days or 20 days or 30 days or one year.And that is it I mean, I need not to wait for the entire system to get dried up or whatever.Write down this question.And my when I am discussing the breakthrough curve, please ask me this question.You will get a better picture.So, "Professor - student conversation starts" like any preferential draining paths are therein clay liner then it will affect the contaminant?Like collection, you are right.So, that always remains there.So, that is the biggest limitation of creating these type of systems where the interfacecomes lesser known devil when I was studying about the MSW landfills liners, in which thechordal provision is like you have a 1.5 meter clay liner.So, is it like 1.5 meters set like for a particular nature depth, so they have given considerationthey actually did that for a typical landfill or is it just a casual number?See, again, as I said, these are the thoughts which are under scanner.So, if a person like me is a consultant, I cannot afford one meter, you know, storagespace in a landfill for creating a liner system.Second question is in today is world, I do not have so much of the clays from where Iam going to bring them when there are strict."Professor - student conversation ends"You know, warnings and what do you call as strictures that you should not excavate soilfrom so, all this is the neo concepts, where I would like to decrease the size of the linerfrom one meter to 2 centimeter.GCL CCLs so first of all the concepts are required and second is alteration of the conceptswill make your ideas more contemporary.In all my consulting projects right now, I am going for, you know, what is the thicknessof the lightness, which I use?3 mm, I cannot lose one meter space of storage multiplied by the whole area of the landfill.How much volume?This would be 1 year or 2 year of storage of the entire Bombay city.It is not 12,000 tons per day what you are talking about 8000 which has come down tonow 6000 per day in Bombay.So are you realizing the concepts and what can be done by using these simple experiments,you know, big, big questions can be answered.Suppose somebody asked you a question that create a thermal barrier.For my building, I can use the same concept what I have to do, rather than percolatingthe water, what I will be doing, I will be exposing this surface to a thermal gradientand then I will measure temperatures over here to tell you whether the whole thermalbarrier is intact or not.So, I got it to PhD thesis based on this concept where we have designed thermal barriers fordefense.These are the applications of the modern-day science and technology.This type of systems are also used for finding out the efficiency of the clay liners, youknow how much they are leaking over there cracking and determine their hydraulic conductivitywhich I have already discussed.Whether they are properly functioning or not, I can put an electronic sensor also at thebottom of the clay liner.So, the moment a certain species of contaminant comes, I can detect it, and this can producea sound or light, or you know, some sort of an alarm.And I know that the line that has failed.So, these type of techniques are being used in contemporary world.