 Here I will be talking about importance of thermal characterization, what are different methodologies which are used for characterizing geomaterials based on their thermal response. And of course, the methodologies which are being used for determining thermal response or thermal characteristics. So, what are these properties of the characteristics? And what is the influence of various soil specific parameters on thermal properties or characteristics of the geomaterials? Now, this will be followed by some discussion on centrifuge modeling of establishing heat flow in geomaterials and of course, the last one would be electrical characterization. So, let me ask you a question here that why we are studying or why we are characterizing geomaterials? Do you remember that why we started characterizing the geomaterials or you have forgotten? What is the basic idea of characterizing geomaterials? Yeah, so, his answer is that based on characterization you can identify the soil that is the bottom line. The whole idea of doing this exercises that we should be able to identify the material based on its response. And if you remember when we were talking about the response of the material we have discussed different energy fields. So, the most common which everybody is using in the classical geomechanics is mechanical energy field. Then we spend enough time on chemical characterization and now we are graduating to thermal characterization followed by electrical characterization. So, the basic idea is as you rightly said by adopting a suitable characterization scheme we want to understand how a geomaterial is going to perform under a given circumstances. So, the circumstances is a very big word. In our discussion or the point of view of our discussion the circumstance will correspond to a different situation or a loading condition. So, you have been talking about mechanical response of the material, load deformation characteristics, stress strain relationship, how word ratios change, how strain changes, how stress is changed and so on. Now, continuing this concept if I use chemical flux which becomes chemical energy field we have seen how porous media is going to respond to or in other words if you know the response we can find out what type of loading is taking place into the geomaterial. So, when we talk about thermal characterization, this characterization is becoming very important because of several real life situations which we encounter in field. Now, what are these real life situations which are now challenging our profession as such? The first one is high level radioactive waste disposal. The stability of the geomaterial itself is under question mark, it is under a big thread if the thermal flux is very very high. So, now, by this time you have enough idea about how these type of waste are going to create problems to the geoinvirement. So, when a high level radioactive waste come in context with geomaterials how this geomaterial is going to behave? If at all it remains intact or if it does not disintegrate, if it disintegrates that is a different issue altogether then response does not come to the picture. So, the survey say thermal flux is very very high, but under normal circumstances when you are dumping a radioactive waste in a repository which could be either soil or which could be intact rock mass, you have to establish the heat bearing capacity of the repository or the material. So, you should note the word heat bearing capacity intentionally I am using this word heat bearing capacity because still now you are talking about bearing capacity which is related to the mechanical loading. So, in this situation it becomes important to understand how geomaterial is going to respond to a thermal flux or thermal loading. The second situation is high voltage underground power cables. The more and more in crystallization is challenging our profession because most of the time high power transmission of current is underground. Now, when you expose underground environment or geo environment with thermal fluxes, how these thermal fluxes are going to change the properties of geomaterials is a very big question and unless you establish this you cannot use the concepts of classical geomechanics properly. A good example of this type situation would be thermal cracking of soils. So, because of the excessive heat which generates because of transmission of electricity in underground power cables, there could be a situation where the soil cracks completely and once the cracking take place the system is exposed to the environment or for population of water and so on. So, this issue is also becoming very very important in most of the industries or in present day civilization. You talk about roads, pipelines, structures in cold regions they also require some input about the thermal response of the material alright. Sometime back I had given an idea about the design of foundations in Antarctica or in the cold regions where the permafrost is quite active. So, you have to estimate the properties of the geomaterials exposed to a different temperature conditions so that you can understand how stable the system would be and hence you can design the foundation system and so on. When you talk about the roads, I think it is understood that most of the time your thermal stresses cause wrapping stresses into the concrete slippers or the concrete pavements. So, you should understand how the situation can be dealt with pipelines. So, these pipelines could be conveying crude oil or some volatile materials like any substance chemical or may petroleum. So, if the ambient temperature rises too much what is going to happen to the crude oil or the chemicals which are being transmitted through pipelines they may become unstable. So, you cannot transmit chemicals from one point to another point if you do not take into account the thermal properties of the geomaterials in which the pipelines are buried. Similarly, there could be an extreme condition where the ambient temperature goes below 0. So, what does indicate to the pipelines may burst or the fluid itself may get frozen into the pipelines again choking them and bursting. So, the problem becomes quite multi fold and that is the reason that in environmental geotechnics or geomechanics people are trying to understand the response of geomaterials for thermal loading. Most of the time when you deal with agriculture or aquaculture. So, this is where the concept of solar pond comes what type of aquaculture should be adopted in a certain region alright or the growth of some bio organisms which are quite useful for either agriculture purpose of a medicinal purpose or for export import purpose or whatever. So, this is where you have to go for energy balance the energy which plants receive from the sun the solar energy and how whether it gets retained into the system or not has to be studied. So, agriculture and aquaculture fields or the solar ponds are also attracting lot of attention of geotechnical engineering and there was a time when we were collaborating with Terry Tata Energy Research Institute for designing their solar ponds and specialized bricks by using some typical type of soils where the energy efficiency factors are very important. Ground improvement techniques. So, in ground improvement techniques particularly when you are talking about the techniques related to soil heating and freezing this is where the thermal properties or the response of the geomaterial for thermal flux becomes very very important. Remember I had given you an example that if you are doing tunneling in fractured rock mass or in highly pervious soils the best option is you freeze the soil is it not. So, by freezing the soil what you are doing you are decreasing the permeability and hence you need not to adopt pumping out methods to drain out water from the tunnels or from excavations and so on. So, these type of methods are very handy in advanced geomechanics these days. Similarly, you can think of soil heating procedure and soil heating can be used for remediating the lands which are contaminated with organic materials. So, the best way would be to heat the soil mass and then what happens all the vapors go out into the ambience you may collect them in a controlled manner. So, that the environment does not get contaminated much. So, these are the applications where you know our focus or our attention is really required. Energy conservation schemes I have already talked about this when you talk about solar ponds different type of refrigeration units different type of bricks for the air conditioning purpose and all energy is becoming a big commodity. So, you think of the bricks which are very energy efficient. So, you require very less air conditioning as compared to outside ambience. Transmission of hot fluids that is the chemicals and the gases this also I discussed just now there could be instability in the material which is being transmitted in the pipelines when the temperatures go beyond a certain point or if the heat is not getting dissipated in the geomaterial easily or efficiently heat lost from the basement of the buildings. Now, this is becoming a very big issue in most of the metros where basements are becoming very important places for several issues particularly multiplexes, good hotels, recreation activities and so on. So, this is where you require maintaining the ambience properly in the basements ok. So, this is where again you have to talk about the geomaterial and the basement structure thermal stability. So, all these issues show that yes the thermal response is becoming a very important factor. Sometimes back I had given you a logic or maybe even one of the situations where if you are designing a foundry all right foundry unit what type of foundation should be adopted whether temperatures are going to be very very high or a forging unit for that matter all right or a furnace. So, if you design a furnace on this soil without talking into without taking into account this thermal property the thermal cracking may take place. So, these are the situations I think you can see they are empty number of situations where the thermal flux plays a very important role in talking about the stability of the geomaterials. So, what are these thermal properties? How would you quantify the thermal response of a geomaterial? The first parameter is thermal resistivity which is the inverse of conductivity k and thermal resistivity is denoted as R subscript t which is the inverse of conductivity k. The second parameter is thermal diffusivity how easily it diffuses from one point to another point into the system. You remember we were talking about diffusion of contaminants and in pore pressure theory we talk about the diffusion of pore water. So, here we talk about thermal diffusivity. So, coefficient of consolidation is nothing but pore pressure diffusion process. Di is nothing but diffusion coefficient in terms of chemical contaminants. Here we are using the term thermal diffusivity the form of the equation of the expression will remain same. The third parameter is specific heat which is denoted as Cp which is the heat storing capacity of the system. Now, let me ask you a question can you correlate thermal resistivity with some very well known geotechnical engineering parameter or for that matter thermal diffusivity and specific heat. A specific heat of water is very high or very less it is your guess or you are sure about it why it is so high your logic is not correct, but answer is correct. So, heat heat capacity of water is high and normally it is 1 unity. So, my question to you is can we use these three terms in characterizing the geomaterials? How did you define hydraulic conductivity? Hydraulic conductivity is the ease with which water can migrate into the porous system. Now, in equivalent form if I use the term rather than say hydraulic conductivity if I say thermal conductivity. So, this is nothing but thermal conductivity k. So, this small k is equivalent of hydraulic conductivity of the porous system. Now, this concept can be utilized for determining hydraulic conductivity of unsaturated soils. How? In your classical geomechanics experiments like following a test what you are doing? You are allowing water to go into the porous media, but suppose if I want to clear unsaturated state of the soil by expelling water out of the porous media it is a reverse process. So, how I am going to do this? If I impose a thermal flux on the soil mass what the thermal flux will do? It will expel the water from the porous media clear. So, expulsion of water is nothing but unsaturated hydraulic conductivity. Ingress or movement of water into the soil mass is nothing but saturated hydraulic conductivity. So, this concept has been used by Dr. Anumant Rao for his PhD thesis and he has shown how these methods can be used in creating unsaturated state of the soil and determining unsaturated hydraulic conductivity of the soil. So, what I wanted to demonstrate here is that these three terms are related to each other and they get mapped over the density rho. So, C p is a inverse function of multiplication of thermal resistivity, density and thermal diffusivity clear. So, if diffusivity is more the specific heat is always less because heat has a tendency to get diffused faster. Similarly, if resistivity is very high what is going to happen? This is going to be less. So, this is where I say that conductivity can be correlated to hydraulic conductivity and the logic I have given you yes now. So, these three parameters become very important to characterize a geomaterial when this geomaterial is getting exposed to a thermal gradient is this part clear. So, you can think of a characterization scheme for the soils where RTK, alpha Cp are known and you should be able to identify what is the constituent of the soil. This again is very challenging work because measuring these properties is a matter of few minutes, but you take any of your classical geotechnical engineering experiment which takes not less than few hours. So, this is where you know these philosophies are becoming very handy and you can characterize the soils mass quickly. So, I will show you in the later half of the lecture today that how these parameters can be utilized in characterizing the soil mass. Let us talk about the factors which influence the thermal properties of geomaterials. The first one is of course, the type of the soil whether the soil is a clay type of a soil is a sandy type of a soil whether it is a rock material or when said mixture or the combination of the two whether it is saturated or not. So, moisture content becomes very important. What is your intuitive feeling? If moisture content is more, resistivity should be more or less. That is right. Why? No, no, no, no, no, no. Please think it again. I ask you a trivial question. If soil is dry, what is in the pores? Air. What about the thermal conductivity of air? It is more or less? It is less. So, that is the reason for dry soils the thermal resistivities will be very very high. And for wet soils thermal resistivities would be less. Of course, when we say type of the soil the distribution and size of the grains plays a very important role. Now, what is your feeling? For fine-grained soils the resistivity should be more or less. Why? Sir, these fine-grained soils are used for a ceramic coating on space shuttles and all those things to have a very high thermal resistivity. Your answer is correct, logic is wrong. Well, the answer is correct that the grains are very fine, the resistivity is going to be much more. Minerals are good conductor of heat or bad conductor of heat? As compared to what? First of all you should ask that question, otherwise question is incomplete. All right. So, truly speaking minerals are bad conductors of heat. So, when we talk about the minerals which are of very fine platelets, their resistivities will be much much more. But when we talk about the coastal material, certain amount of mineral gets replaced by air and the resistivity of air is higher than the minerals, but lesser than water. So, that series comes into the picture and hence you will notice when you work on fine-grained soils the resistivities are going to be much more. Now, why it is important to study the resistivity of the soils? If you bury a cable which is conveying certain amperage, amperage means certain amount of current is getting passed through this cable and if resistivity happens to be very high, what is your imagination? What is going to happen to the cable? You think of a situation where all about the cable the temperature rises too much because of passive the current. So, what will happen? The cable itself may melt all right and once the cable melts, you cannot convey any current from one point to another point. So, this is situation where you require a system which dissipates heat which is getting generated into the soil mass or in the porous media because of conveyance of the current very quickly. So, resistivity for a good deposit in which the cable trenches should be laid should be very very less. In technical terms, this is what is known as ampicity of cables that means, the ampicity of the cable should be very high. So, whatever current is being input in the cable the same should come out at another end 100 kilometers, 200 kilometers, 500 kilometers away. If there are losses because of resistivities of the soil you know you are losing energy, you are losing money and so on and that is why most of sites are selected based on not only their geotechnical parameters, the major issues for industrialization is the thermal resistivity of the soil and that is one of the reasons why most of good companies in the country could not establish their bases in most of the part of the countries because the ground conditions are very very poor. A classic example is of Hyundai. Hyundai earlier wanted to come and settle down in Kerala, but it could not apart from some political reasons because the ground conditions were really very bad all right and they selected another place where the you know chain edge all along the chain edge the resistivity values were either not changing too much or good enough for laying a good cable line. Another good example is your cross country pipeline from Gujarat to where? Iran. Yes that is a very big project which is going on in India right now. Sikon India Limited is doing that work. So, this is where actually the type of the soil moisture content, distribution of the size and the grains of the soil becomes a very important parameter in finding out whether a project is feasible or not because there is a limit to modify the soil based on its thermal properties. And when you say modification of the properties it is understood that you are trying to lower the resistivities clear. So, in a region like Bombay or most of the coastal regions where you have clays the thermal resistivities are very very high. So, you have to modify the entire root of the pipeline or the buried cable ok, kilometers long by inserting a good material which is known as a good backfill material or fluidized thermal bed material FTBs. If you work sometimes in this area you will come across a word which is known as FTB fluidized thermal beds. So, fluidized thermal beds are designed to reduce resistivities of the soil mass. There is a paper by Dr. Kole and myself in ASC where we have designed fluidized thermal beds using fly ash and clays it must be in 2001 or 2002 ASC. The another parameter is density of the soil. Now, what is your intuitive feeling if density is more resistivity should be less or more. How can if density is more resistivity can how can it be more? If density is more the air will be less the point to point contact will be more alright. So, the resistivities are going to be less. Temperature and pressure, temperatures and pressures are also going to affect the resistivities. Do you remember the linear resistance equation as a function of temperature rise RT equal to r naught plus 1 plus alpha into delta theta. So, the moment temperature rises what happens to the resistance? The resistance increases. If resistance increases what happens to the current for the same voltage it will drop down. So, you think of a situation where you are excuse me where you are designing a industrial unit and where you want to convey certain amount of voltage or a current, but because of very high resistivity of the geomaterial the temperature of the cable increases. So, if temperature of the cable increases what happens to the resistance? Resistance increases and then what happens to your current passing from one point to another point it drops down. So, all these issues are very important when you design industries in problematic soils alright is this ok. Presence of contaminants, the presence of contaminants can also influence the resistivities of the soils. Method of measurements, what type of method of measurement is being employed to measure thermal resistivity. So, because these issues are quite young you know in historical time young in the sense they are not more than say 20-25 year old issues. So, still people are trying to establish the methods, the methodologies, the interpretation of the parameters and so on. So, that is what I say that the method of measurements play a very important role in coming across the properties of the material establishing the properties of the material. Now, all these parameters indicate that specific heat, thermal resistivity and diffusivity because they depend upon these parameters they can be utilized to characterize them in the best possible manner. A good example of this type of characterization is if you go through the published work by the Bhutidas who did his PhD he has characterized concrete based on their thermal properties. So, that was also a very interesting way of characterizing the you know durability of concrete or the porosity of the concrete based on thermal flux. Now, let us talk about the methods for estimating soil thermal resistivity. The first method is grouped as laboratory method and the second one is field method. So, within laboratory method it is a guarded hot plate method which is normally not used these days. The reason is this was a technique where you have a hot plate like the one which you use for making chapatis at home is it not. So, you have a hot plate put the material on the top of that and then let there be a thermal equilibrium which itself is under question mark the entire system is exposed to the environment and then measures the temperatures which are building up in the material. So, I think you can understand that this is a very crude way of defining a parameter, but yes it has been recorded because there was lot of experiments done by people using graduated guarded hot plate method. Another one is a row meter. What is a row meter? What is meant by rho? Rho meter is basically a viscosity measurement equipment. So, if you can measure the viscosity of a system under elevated temperatures you can always find out what are its thermal properties because viscosity is highly linked with temperature. So, again this method happens to be a very very crude way of defining the thermal properties. Now, under these circumstances the transient method becomes the most handy and useful method and our group has done lot of work in transient methods. So, most of the findings of my students I will be presenting into this presentation and showing you how transient methods can be utilized for determining all the three parameters simultaneously. As far as field measurements are concerned you cannot do guarded hot plate method. Of course, some people have tried by inserting a hot plate into the soil mass and then heating it and then measuring the temperatures and the geomaterial. So, what are the advantages of the transient method? The first first of all let me ask you a question what is meant by a transient method? See ours saints and sages they use the word life is transient. What is the meaning of this word? Not limit not permanent transient means something which is momentary. So, this is just for few moments. So, that means the transient method uses the philosophy that you heat the soil mass for a certain moment clear. In technical term this is also known as pulse of heat or pulse of heat flux being imposed on the geomaterial. Is this part clear? For a certain moment. So, certain for moment could be 1 minute, 2 minute, 5 minutes, 10 minutes, but not more than that much not more than few minutes say 20 minutes 15 minutes. Now, within this duration the moisture may change if your heat flux is too much. So, the basic idea is you do not want the moisture content of the soil mass to get changed is it not otherwise you will be creating unsaturated state of the material. So, the beauty of this transient method is you can control the flux intensity, you can control the temperatures and you can control how moisture is migrating along with the heat which is a coupled phenomena. If you remember sometime back I had coined this term coupled phenomena is a phenomena where a moisture migrates from the porous media as well as the heat migrates into the porous media. So, both the things are migrating simultaneously and hence this process is a coupled process. So, idea is this method gives me or gives a researcher or a practitioner a good control over state of the soil. You can play with the flux so, that the moisture does not change at all. You can apply the flux for a certain moment so, that no major changes are undergoing into the system. So, migration of the moisture will not take place and of course, this is a very quick and convenient method of determining thermal properties of geomaterials or the porous media. So, what is the transient method? The transient method is based on a probe like this. The basic intention of showing you all these techniques is to make you realize that people like you have done all this few years back ok. So, this was devised by my one of his students Gangadhar Rao that was in 1996 or 97 I suppose long back. And we have now monopoly in the entire world I should use the word and thermal measurements nobody does this so, precisely except for us. It is a good scope to see that there is lot of scope for instrumentation in geotechnical engineering and instrumentation can be done by all of us. You need not to import anything from anywhere. So, it is a simple copper tube of 95 mm length and diameter about 6 mm. And in this tube we have installed one nichrome wire and the tube at the end has a conical shape. So, that it can be inserted into the soil mass very easily. And ultimately what you do is you put a thermocouple inside the probe it is a t-type thermocouple and then connect it to some readout unit. So, that you can measure what is the temperature at the surface of the probe when it is inserted in some geomaterial. And then these two leads are power supply leads. So, through this the power is supplied to the nichrome wire. So, it is a simple of heat flux that is q equal to I square r where I is the current r is the resistance of the nichrome wire. Now, the basic idea of having this copper tube is that you are having an isothermal surface that means the temperature all along the tube body is same. And then this becomes a typical axisymmetric case of heat flux all right that means the temperatures are going to vary only in the r direction where r is the radial distance of a point from the middle of the probe is this correct. Now, this is the thermocouple yeah. So, here you can see this the nichrome wire passing through and this is the thermocouple which is connected to the readout unit from where you can measure temperature. And this is a typical thermocouple which is inserted inside. So, you can understand that in 6 mm diameter probe we are inserting everything. And this probe now we are actually marketing to the Norwegian Electricity Bolt yes. So, this is our copyright and the at the end of this thermocouple there is a grounded junction which you can see over here. So, this is a point which reads the temperature. So, the both the things are fitted in the system. So, once you load out this probe in the material you can measure temperature on the surface of the probe. Now, why I am emphasizing is that you are measuring the temperature on the surface or at the contact of the geomaterial and the surface of the tube or the copper tube because this becomes a boundary condition. The radius of the probe becomes a boundary which is a isotherm where you are measuring the temperature you got the point. So, if I use differential equations to solve this I will be knowing at least one point where the temperatures are measured. So, if it is a second order differential equation what I need to do is I need to measure temperatures at two points in the soil mass. So, one point happens to be on the surface of the probe and the contact point of the material and another temperature I can measure in the geomaterial somewhere at a distance of r. So, if I know the two temperatures if I know the two r values I can solve any differential equation. I hope this concept is clear. Well, this is a closer look of the thermocouples which have been used and the probes which were developed alright. So, these are the probes which we are been using quite a lot in our day to day activities. This your cross country pipeline between Jamnagar to Iraq some place this was also done by us the whole mapping of the soil mass for the thermal resistivity approximately 1500 kilometer long distance. Now, this is a field probe which was developed by another student known as David. This is 1 meter long field probe this can be inserted into the soil mass and you can probe the temperature profile of the soil mass up to a depth of 1 meter. This is the electronic circuitry which here power supply the timer the constant power supply and the temperature readout units. So, only thing is there are three thermocouples installed within this 1 meter where you can measure the temperature and you can find out the contrast in the thermal properties of the geomaterials even layer wise. So, very useful tool which we have been using quite a lot in our day to day activities. Now, this is a device which was developed by one of my PhD scholars Dr. Krishnaia who is now J&T which is only in department Anandpur. So, this is thermal property detector. So, thermo detector we call this device as thermodact. It is a tube about 70 millimeter diameter hollow tube both the ends are you know sealed with the help of a styrofoam and in the styrofoam you can fix a thermal probe which I have shown you just now. The beauty of this setup is that you can seal up the soil mass in the powdered form or in the core of the soil in this space and you can insert the probe all right. You can apply current so that the entire material gets heated up inside and then you can measure the temperature over a period of time. Now, this is what is known as heating cycle. Another way of interpreting the results would be you pack the geomaterial in this system along with the thermal probe and the thermocouple and keep the entire unit in a oven. I will show you the results what we have got. So, what happens? The entire system gets heated up up to a certain temperature and then we can use this device for measuring the temperature inside the material. Now, this again is the heating cycle. Later on you can take out this device from the oven and put it in a water bath ok and then this is the cooling cycle. So, still I can measure the temperatures within the soil mass for the cooling. I will show you that how these two different mechanisms have been utilized in interpreting some parameters which are related to the soil mass admixtures. Particularly this device was used for finding out the thermal properties of admixtures in cements and this project was basically done for Kaiga atomic power plant for designing their roof shells and the atomic shells. They had some specifications for thermal resistivity and we had done this job for them. So, working principle is almost same. Now, these are the photographs of the devices which are developed. This is a laboratory thermal probe, this is the dummy rod. So, you make a proctor sample, use the dummy rod which is slightly lesser than diameter than the thermal probe. You create a dummy hole and then fix this probe into that and then you can go ahead with your experiment. Very simple device. This is extended form of the laboratory thermal probe which is field thermal probe where we use a mold of 1 meter length and diameter is about 30 centimeter. This device was used for measuring the sandy soils particularly and gravelly soils and gravels because you can can appreciate the point that gravels cannot be tested in this type of setup. So, you require almost 1 meter long rod to check the thermal conductivity of gravels. This paper was published in ASC. So, you can refer it whenever you need and this is the device is thermo thermodate which I have shown you just now. This is the unit made up of stainless steel thermal probe which is inserted into it. This is the temperature readout unit and this is the power supply unit which heats up the nichrome wire. So, these are very simple devices which can be used or which can be developed as per your requirement for doing various geotechnical investigations. And based on the findings of these results we developed one software which is known as DD thumb. The first D corresponds to my students name David and other D corresponds to my name and then this is the thermal property detector. So, we use this software for finding out the thermal properties of a geomaterial. If you know the basic ingredients of the soil like organic components, inorganic components, particle size distribution, density, moisture content, state of compaction, you have to just need to put this in the software and gives you the resistivities.