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Pollution Processes and Soil-Pollution Interaction

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Video 1: Conventional Geomechanics
These are the different processes you know, pollution processes and soil pollution interactionso, pollution occurs in 3 ways or these are the 3 pathways; air pollution, water pollution,land pollution alright and when we talk about air pollution, this is the smoke and odourwhich is big issue incineration of solids will cause this industrial gases are a bigissue, 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 contaminatedsurface you know and groundwater, chemical waste, oil pollution, silt in water becauseof run off, nutrients in run off, there was the time in nutrient, nobody is talk aboutbut now nutrient is also becoming a part of the geotechnical engineering because if youremember a good example would be C and Phi parameters depend largely on the nutritionalcapacity of the soils, cementing property.And coefficient of C or C parameter depends upon you know, different types of chemicalswhich are present in the soil particularly carbonates and sometimes sulphates which arebonding the soil particles together.Land pollution; we talk about dumps, chemical wastes, power plant waste, septic tanks youare 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 pollutionoccurs we have accelerated weathering of either concrete or cement, we talk about the corrosionof the buildings, we talk about the bridges, pavements and acid rains recently, there werea lot of bridges which were failing which had failed in Calcutta, I hope you must haveand if you see my report which was published by the local papers have made you know pollutionas the main reason responsible for the collapse of the bridges poor maintenance of the bridges.These are worth reading examples, so this is all the subject is involving you know earlierpeople used to say that these are only the strength of the concrete, the strength ofthe concrete is getting affected because of pollution ingress, if water is polluted andif this water you are using for making concrete, then durability and workability of the concretewill change.Soil water system is going to get influenced, hydraulic conductivity is going to be differentand hydraulic structures get affected, a good example of acid mine drainage which you aretalking about is; if the water has a non-neutral pH value, it is going to change the shearstrength parameters of the soil, enough studies which are available in the literature particularly,for water happens to be acidic, what will happen to these calcium carbonate which waspresent in the soils as a binding agent.So, the pH, which is less than 7, acidic water influences the cohesion of the soil and henceparticle become erosion prone and the more and more erosion occurs you know, there willbe first void and later on there could be a collapse.So, when you talk about the land pollution this is what explained just now because ofthe pollution of the soil, hydraulic and thermal conductivity is change.This is the first time I am using the term thermal conductivity and later on we willrealize that why thermal conductivities are important because these are the fundamentalbehaviour how heat migrates through the system, soil compaction changes because of the presenceof contaminant, settlement, stability, seepage characteristics, everything changes, thisis 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 pollutionform, you are aware of most of these issues.Now, let us hit at the conventional geomechanics alright because if you want to include allthis discussion which I have been doing, we have to go into the micro details of whatare the basic concepts of the analysis in geomechanics.So, the concept number 1 is that most of the structures in geotechnical engineering occurin nature alright, they are not shielded, so they are exposed to the nature, sunlightyou 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 comparedto other construction material.One good example is presence of organic matter so, if organic matter is present during veryhigh temperatures or low temperatures and humidity, this combination is going to bevery critical.So, when systems are sitting in the nature, we have to talk about the long-term performance.Experiment which you do in the laboratory for a few hours or few days is not going togive you a complete response, so this calls for long term testing and long term testingcould be for few 10’s of years, you will find data which is which runs of the experimentalplant for few 10’s of years or 100’s of years even.The second one is the soil is more sensitive and hence what we should be doing?We should be talking about various factors which are influencing its fundamental behaviourlike stress-strain relationship, crushing characteristics so, these factors have notbeen directly included, so I will be very eager to understand you know when soil comesin contact with elevated temperature, low temperatures how their elastic modulus changes,Poisson’s ratio changes, how their constitutive laws change, the stress-strain relationshipschange 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 severetemperatures would also create the dry state of the material, so there is a loss of strengthyou know starting from saturated to dry to totally partially dry state whatever, so itis very important to study what moisture ingress does to the system.And what moisture egress comes to the system and of course, the basic agenda is to seehow pollution interacts with the geomaterials 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 whenI say flaws, why I am using the word flaws because the conventional geomechanics cannottake into account the issues which we have discuss until now, so now the time has cometo understand the limitations and once you understand the limitations of the status ofthe subject, you try to go beyond this.And you trying to complement this with your knowledge or with your experience, so nowpresently what happens is; I am sure you must have realized that specific gravity and Atterberg’slimits are always constant we assume, we never thought that the interaction is taking placeand 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 typesof chemicals or compounds and hence special gravity does not remain constant alright andthe second issue is that your Atterberg’s limits will also change because if the waterand its constituents change the Atterberg limits cannot remain constant, this is whathas been overlooked.Another thing is that we always treated the porous media as a standard porous media, wenever bothered about decay of the voids, we never talked about the decay of the material,we never talked about the up gradation of the material though what bacteria does, Ithink you have cited ample examples where the bacteria eats of the soil mass and hencecreates 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 ischanging this is correct.Now, sometime back I gave you a hint in today's lecture that the way we have considered waterin geomechanics, conventional geomechanics is not correct because the water cannot beonly water; water is basically environmental water.Because it is an attribute of the environment present in the system and this water couldbe in different forms, vapour form, stream formation so, when soil comes in contact withlet us say high temperatures what happens; certain fraction of the moisture which ispresent in the soil gets converted into vapours and these vapours tend to migrate throughthe 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 thefree form in the soil and that is what we have dealt with, so contemporary geo mechanicsdeals 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 differentiatebetween 3, 4 types of water which is present in the soils.And that is what we will deal with subsequently, now you must realizing the subject is becomingslightly more intricate, is it not so, I am sure unless you like chemistry and the chemicalprocesses which occur in a matter, you cannot deal with these type of issues because thewater which was present in the pores at a certain temperature now gets converted intoseveral phases of the water, it is a chemical process.And this chemical process might trigger because of let us say dumping of some industrial by-producton the soil mass, so there is a chemical species which might exhibit exothermic reaction.So, when it comes in contact with the water, the temperature gets enhanced, elevated andthis process might trigger the temperature in the soil mass, and this coupled phenomenamethod.So, most of the time, the landfills and the waste which is being dumped in the landfillswhen suitable environmental conditions get created, they become reactors, sometimes explosionalso occurs in landfills, why; the gas has got trapped inside and they blast alrightor the temperatures of the landfills are so high, it is just like a furnace which youare 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 the environmental geotechnologist.We have very simplified way of dealing with the flow of water, Darcy’s law, is it not,we just defined 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 onlycauses 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 soilsto an energy field that flux migrates because of the flux gradient, so we have ignored allother types of flux cells which the soils might get exposed except for one which ishydrostatic, 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 Hupon L is equal to hydraulic gradient.So, you have to now talk about the flux velocity as the coefficient of energy conductivitymultiplied by the energy gradient.So, in Darcy's law energy gradient is I; delta H upon L, coefficient of energy conductivityis 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 realisticsituations.I have not included here bacterial flux remember because what bacteria does in the soil iswonderful thing, it might create a lot of interesting and intriguing things, alright.Now, another thing is the constitutive models; constitutive models are stress-strain relationships,so I am sure you must have realized in 1, 2 and 3 are valid, the constitutive modelscannot remain constant.So, truly speaking sigma and epsilon and the coefficient which is balancing the 2 are alla function of time, is it not, so your constitutive models are going to change when these conditionsget violated is this okay, fine.So, stress-strain relationships are also going to change because the material has changed,you cannot use the same stress-strain relationships, so unfortunately in the conventional subject,there is no way to imbibe all these concepts.


Video 2: Soil Classification
Some other issues which are under scanner,the constant seepage velocity you know when terzaghi geomechanics say that the velocityand hydraulic coefficient and the CV do not remain constant, coupled processes we haveignored 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 gave you ample examples that acidulated water or water at a lower pH is detrimentalto the health of soil mass be it embankment or whatever, so the chances are that the coupledprocess may occur, the mass flux may take place or the energy flux method.Another good example would be let us say, the soils which are what do you call themas you know dispersive soils.So, you must have come across double hydrometer test which are done on dispersive soils toget their particle size distribution, saturated versus unsaturated conditions alright, inthe soil mass, this is a big subject where we talk about unsaturated state of the soilmechanics, we have treated soils as inert but soils are not inert, so this is what hasto 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 behavewith a certain cation or anion which is present in the soil mass and of course, the biochemicaldegradation of geomaterial which we have not talked about which is very, very importantfor the case when we are dealing with the soils and of course, everything which is timedependent, so how this degradation and up gradation is going to occur as the time goesup.So, I am sure you must be realizing now, the environmental geomechanics a scope is quitetricky and you know very vast, the sky is the limit, whatever comes to our mind youcan include it.Now, the question is; whatever soil classification you are following whether it is acceptableor not so, presently what we do is we are including these parameters for classificationof the soils, we talked about grain size distribution for coarse grained materials and we talkedabout the fine grained materials you know the parameters like consistency limits, LL,PL, PI mostly and this is the guiding criteria for understanding the fundamental propertiesof soil.The gross injustice with the material like soils which we have studied and used by thistime so, the question is what should be the scenario, how many parameters we have to includeto understand this material in a comprehensive manner and the answer comes from here; thephysics of the material is passing through 200 microns sieve, clear or 200 number sieve,then if you want to quantify the physics of the material, then you have to talk aboutthe specific surface area.And specific surface area I hope you understand is the total area divided by per unit weightof the material and then comes the pore fluid characteristic, the pH particularly of thesoil, so chemistry part of the material, then ion exchange capacity, cation exchange capacityagain, this is a chemical; chemistry part of the material.So, physicochemical processes; these are the physical processes, these are the chemicalprocesses.How interaction occurs with the environment is the sorption capacity, mind the spellingclearly, this is the sorption and this sorption includes absorption and adsorption, so wewill talk about these processes.So, one is a physical phenomena absorption, adsorption is a chemical process and so onand then we have to talk about the electrical properties like conductivity and electricconstant of the material.Because conductivity itself is a function of dielectric constant and dielectric constantis mineral dependent and this is a question which you are talking about, so truly speakingwhen you talk about the dielectric constant of the material, the magnetic properties getinbuilt in the system, alright and of course, thermal diffusivity, resistivity and heatcapacity.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 radiationshere and I have not taken into account the effect of biological processes here, so themore and more you add over here, the system becomes more and more comprehensive, so Iam sure that you will realize that this subject is going to grow for several years.Today, I am hope this must have given you a fair idea about that why environmental geomechanics is a must in today's context.“Professor – student conversation starts” Sir, why have you taken that 200 micron sizeonly, that is a physical property just the crane size only in shape, like why 200 microns,practice, yeah 475 you know micron is equivalent to 200 sieve size, so this is nothing butthe what is written in the literature, so 475 micron is equivalent to 200 sieve size.