 These are the different processes, you know, pollution processes and soil pollution interaction. So pollution occurs in three ways or these are the three pathways, air pollution, water pollution, land pollution, alright. And when we talk about air pollution, this is the smoke and odour which is big issue incineration of solids will cause this. Industrial gases are a big issue, radiations are big issue, sewage odours, vehicle exhausts are a big issue, pesticides sprays and dust is a big problem. When we talk about the water pollution, contaminate surface, you know, and groundwater, chemical waste, oil pollution, silt in water because of the runoff, nutrients in the runoff. Whenever the time when nutrient nobody used to talk about, but now nutrient is also becoming a part of the geodecine engineering because if you remember a good example would be CN5 parameters depend largely on the nutritional capacity of the soils, cementing property and coefficient of C or C parameter depends upon, you know, different types of chemicals which are present in the soil particularly carbonates and sometimes sulphates which are bonding the soil particles together. Land pollution, we talk about dumps, chemical waste, power plant waste, septic tanks, you are talking about chemicals in soils and food, erosion and agricultural manure. Now, what is the effect of these type of pollutions on the engineering behaviour? When air pollution occurs, we have accelerated weathering of either concrete or cement, we talk about the corrosion of the buildings, we talk about the bridges, pavements and acid rains. Recently, there were a lot of bridges which were failing, which had failed in Calcutta, I hope you must have. And if you see my report which was published by the local papers, I have made, you know, pollution as the main reason responsible for the collapse of the bridges who are maintenance of the bridges. These are worth reading examples, so this is how the subject is evolving, you know. Earlier people used to say that this is only the strength of the concrete, the strength of the concrete is getting affected because of pollution ingress. If water is polluted and if this water you are using for making concrete, then durability and workability of the concrete will change. Soil water system is going to get influenced, hydraulic conductivity is going to be different and hydraulic structures get affected. A good example of acid mine drainage you were talking about is if the water has a non-neutral pH value, it is going to change the shear strength parameters of the soil, enough studies which are available in the literature. Particularly water happens to be acidic, what will happen to these calcium carbonate which was present in the soils as a binding agent. So the pH which is less than 7 acidic water influences the cohesion of the soil and hence particle become erosion prone and the more and more erosion occurs, you know, there will be first voids and later on there could be a collapse. So when you talk about the land pollution, this is what I explained just now because of the pollution of the soil, hydraulic and thermal conductivities change, this is the first time I am using that thermal conductivity and later on you will realize that why thermal conductivities are important because these are the fundamental behaviour how it migrates through the system. Soil compaction changes because of the presence of contaminants, settlement, stability, see patch characteristics, everything changes, there is a big matrix, you know, how pollution changes the fundamental properties of the geomaterials and whether it is in the air pollution form, water pollution form or in the land pollution form, you are aware of most of these issues. Now let us hit at the conventional geomechanics, alright, because if you want to include all this discussion which I have been doing, we have to go into the micro details of what are the basic concepts of the analysis in geomechanics. So the concept number one is that most of the structures in geotechnical engineering occur in nature, alright, they are not shielded. So they are exposed to the nature, sunlight, you know, water, different type of attacks of chemicals and so on. And hence another concept is that the soil is susceptible to the environment as compared to other construction material. One good example is presence of organic matter. So if organic matter is present during very high temperatures or low temperatures and humidity, this combination is going to be very critical. So when systems are sitting in the nature, we have to talk about the long-term performance. An experiment which you do in the laboratory for few hours or few days is not going to give you a complete response. So this calls for long-term testing and long-term testing could be for few tens of years. You will find data which is, which runs of the experimental plan for few tens of years or hundreds of years even. The second one is soil is more sensitive and hence what we should be doing, we should be talking about various factors which are influencing its fundamental behavior like stress strain relationship, crushing characteristics. So these factors have not been directly included. So I will be very eager to understand, you know, when soil comes in contact with elevated temperature, low temperatures, how their elastic modulus changes, poisons ratio changes, how their constitutive laws change, stress strain relationship changes and so on. What is the influence of the moisture? So when soils get exposed to high temperature, the moisture is going to change and severe temperatures would also create the dry state of the material. So there is a loss of strength, you know, starting from saturated to dry to totally, partially dry state, whatever. So it is very important to study what moisture ingress does to the system and what moisture excess comes to the system and of course the basic agenda is to see how pollution interacts with the geomaterial and what ultimately happens to it, alright. So these are the basic concepts which one has to understand of the analysis. And then let us talk about what are the flaws in the conventional geomechanics. And when I say flaws, why I am using the words flaws because the conventional geomechanics cannot take into account the issues which we have discovered until now. So now the time has come to understand the limitations and once you understand the limitations of the status of the subject, you try to go beyond this and you try to complement this with your knowledge or with your experience. So now, presently what happens is I am sure you must have realized that specific gravity and atter bug limits are always constant, we assume. We never thought that the interaction is taking place and the material is changing and hence specific gravity is changing, it could be dissolution, it could be crystallization taking place in the soils of different types of chemicals or compounds and hence specific gravity does not remain constant, alright. And the second issue is that your atter bug limits will also change because if the water and its constituents change, the atter bug limits cannot remain constant. This is what has been overlooked. Another thing is that we always treated the porous media as a standard porous media, we never bothered about decay of the voids, we never talked about the decay of the material, we never talked about the upgradation of the material, though what bacteria does, I think we have cited ample examples where the bacteria eats up the soil mass and hence creates voids. So void ratios are changing, porosity is changing, this does not remain constant and when the void ratios and porosities are changing, the shear strength is changing, compressibility is changing, consolidation characteristics are changing, everything is changing, is this correct? Now sometime back I gave you a hint in today's lecture that the way we have considered water in geomechanics, conventional geomechanics is not correct because the water cannot be only water, water is basically environmental water because it is an attribute of the environment present in the system. And this water could be in different forms, vapor form, stream formation. So when soil comes in contact with let us say high temperatures, what happens, certain fraction of the moisture which is present in the soil gets converted into vapours and these vapours tend to migrate through the voids, clear? Solidification of water, freeze and thaw cycle. So water we have not dealt with properly, we have always talked about the free water, the gravity water in the, present in the soil mass, you mix something which remains in the free form in the soil and that is what we have dealt with. So contemporary geomechanics deals with the bifurcation of the water which is present in the soils. There are techniques by which of course very advanced techniques by which we can differentiate between 3-4 types of water which is present in the soils and that is what we will deal with subsequently. Now you must be realizing the subject is becoming slightly more intricate, is it not? So I am sure unless you like chemistry and the chemical processes which occur in a matter, you cannot deal with this type of issues because the water which was present in the pores at a certain temperature now gets converted into several phases of water, it is a chemical process and this chemical process might trigger because of let us say dumping of some industrial byproduct on the soil mass. So there is a chemical species which might exhibit exothermically action, so when it comes in contact with the water the temperature gets enhanced, elevated and this process might trigger the temperature in the soil mass and these coupled phenomena may occur. So most certain the landfills and the waste which is being dumped in the landfills when suitable environmental conditions get created, they become reactors, sometimes explosion also occurs in landfills, why? The gases got trapped inside and they blast off alright or the temperatures of the landfills are so high it is just like a furnace which you are designing which is going to be sitting on the surface of earth or ground alright. So these are the intricate issues that you have to deal with as environmental geotechnologists. We have very simplified way of dealing with the flow of water Darcy's law is it not? We just define the hydrostatic potential which causes flow of water to take place. Now slowly and slowly you will realize that it is not the hydrostatic pressure which only causes the flow of water through the soil mass or the mass flux. Soil water intrusion is a big example you know, whenever you are exposing the soils to a energy field that flux migrates because of the flux gradient. So we have ignored all other types of fluxes which the soils might get exposed to except for one which is hydrostatic you agree? So now the time has come that we should be talking about the chemical flux, thermal flux, electrical flux you know, magnetic flux apart from the mechanical flux which is delta H upon L is equal to hydraulic gradient. So you have to now talk about the flux velocity as a coefficient of energy conductivity multiplied by the energy gradient. So in Darcy's law energy gradient is i delta H upon L coefficient of energy conductivity is the hydraulic conductivity k and v is the velocity alright, seepage velocity. So similarly this influence of all the energy fields has to be taken into account for realistic situations. I have not included here bacterial flux remember because what bacteria does in the soil is wonderful thing, it might create a lot of interesting and intriguing things alright. Now another thing is the constitutive models, constitutive models are stress and relationships. So I am sure you must have realized that 1, 2 and 3 are valid, the constitutive models cannot remain constant. So truly speaking sigma and epsilon and the coefficient which is balancing the two are all a function of time, is it not? So your constitutive models are going to change when these conditions get violated, is this okay, fine. So stress and relationships are also going to change because the material has changed, you cannot use the same stress and relationships. So unfortunately in the conventional subject there is no way to imbibe all these concepts and hence you have to look for something interesting. Some other issues which are under scanner, the constant seepage velocity, you know when Razzagian geomechanics says that the velocity and the hydraulic coefficient and the CV do not remain constant, coupled processes we have ignored completely because we have never talked about the heat and moisture flow together, we have not talked about the fines migrating out of the soils, this is the mass flux alright. So I will give you ample examples that acidulated water or water at a lower pH is detrimental to the health of soil mass, beat embankment or whatever. So the chances are that the coupled process may occur, the mass flux may take place or the energy flux may occur. Another good example would be let us say the soils which are what you call them as you know dispersive soils, so you must have come across double hydrometer tests which are done on dispersive soils to get their particle size distribution. Saturated versus unsaturated conditions alright in the soil mass, this is a big subject where we talk about unsaturated state of the soil mechanics. We have treated soils as inert but soils are not inert, so this is what has to be depicted with the help of cation exchange capacity of the soils. The mineralogy has to come in picture you know how a certain mineral is going to behave with a certain cation or anion which is present in the soil mass and of course the biochemical degradation of the geomaterial which we have not talked about which is very very important for this case when we are dealing with the soils and of course everything which is time dependent. So how this degradation and upgradation is going to occur as the time goes up. So I am sure you must be realizing now the environmental geomechanics scope is quite tricky and you know very vast sky is the limit whatever comes to your mind you can include it. The question is whatever soil classification you are following whether it is acceptable or not. So presently what we do is we are including these parameters for classification of the soils. We talk about grain size distribution for coarse grain materials and we talk about the fine grain materials you know the parameters like consistency limits LLP, LPI mostly and this is the guiding criteria for understanding the fundamental properties of soil, gross injustice with the material like soils which we have studied and understood by this time. So the question is what should be the scenario? How many parameters you have to include to understand this material in a comprehensive manner and the answer comes from here. The physics of the material is passing through 200 micron seed clear or 200 number seed. Then if you want to quantify the physics of the material then you have to talk about the specific surface area. And specific surface area I hope you understand is the total area divided by per unit weight of the material and then comes the pore fluid characteristics the pH particularly of the soil. So chemistry part of the material then ion exchange capacity, cation exchange capacity again this is a chemical chemistry part of the material. So physical chemical processes these are the physical processes these are the chemical processes. How interaction occurs with the environment is a sorption capacity mind the spelling clearly this is a sorption and this sorption includes adsorption and adsorption. So we will talk about these processes. So one is a physical phenomena absorption, adsorption is a chemical process and so on. And then we have to talk about the electrical properties like conductivity and dielectric constant of the material. Because conductivity itself is a function of dielectric constant and dielectric constant is mineral dependent and this is the question which you are talking about. So truly speaking when you talk about the dielectric constant of the material the magnetic properties get inbuilt in the system alright. And of course thermal diffusivity resistivity and heat capacity. So if you include all these parameters then only we are doing justice. Of course you can always say that I have not taken into account the effect of radiations here and I have not taken into account the effect of biological processes here. So the more and more you add over here the system becomes more and more comprehensive. So I am sure that you will realize that this subject is going to grow for several years today. I hope this must have given you a fair idea about that why environmental geomechanics is a must in today's context. Sir, why have you taken that 200 micron size only? That is a physical property just the crane size only in shape. Still like why 200 micron? Practice. Yeah, 475 you know micron is equivalent to 200 sieve size. So this is nothing but the what is written in the literature. So 475 micron is equivalent to 200 sieve size.