 We have been talking about geomaterial characterization and which is quite prolonged, you must have realized and what we did is we studied the physical characterization, morphological characterization, mineralogical characterization and then we spend lot of time on chemical characterization. There is a misconception that environmental geotechnology deals a lot with the chemistry, but I am sure that you will realize that without chemistry nothing is possible in today's world. See, even if two people meet, we say there is a good chemistry gelling them together. So, this is the fact of life, biosciences have become very important. Similarly, the applied chemistry is becoming very important because environment is all about how the chemicals are influencing it. Now, in this context, maybe the next in series is the thermal characterization and which is quite a physical phenomena. Most of you must have studied the concepts of heat migration through materials. We are going to extend this information and knowledge to the heat migration through geomaterials, but before we do that, it is important to understand how to characterize geomaterials based on their thermal properties. In other words, when geomaterials are exposed to thermal gradients or thermal field, how do they respond? So, its importance we will be studying methodologies which are used or employed for thermal characterization of geomaterials. What are the thermal properties of importance then influence of various soil parameters on thermal properties of the geomaterials and followed by a bit of centrifuge modeling and one of the applications of thermal properties in geomechanics and environmental geomechanics is the cracking characteristics of soils. So, I will spend some time on discussing the cracking characteristics which are nothing but an indirect implication of the swelling and shrinking characteristics of the soils. And this is where I will also try to emphasize on the fact that gone are the days when swelling and shrinking characteristics of the soils used to be unwanted properties. In the contemporary application of geotechnical engineering and environmental geotechnology, if the soils are passive, they are not swelling and shrinking, they are not supposed to be a good material. So, the context has changed completely. And having done this, we will come back to the electrical characterization and magnetic characterization. So, to begin with the thermal characterization of geomaterials, what is the importance and what are the real life situations where you will be using these concepts. Some of these situations are listed over here. So, the first and foremost is the high level radioactive waste disposal which we have discussed quite in details in the initial lectures of the course. And I have been citing this example since then that the modern day geotechnical engineering is more towards thermo hydromechanical coupling. And hence the thermal effects become very, very important when we deal with the geomaterials which are going to contain the toxic waste or the radio nuclear waste. High voltage underground power cables, the more and more industrialization is taking place in the country. The more and more need is to electrify the industries as well as the societies as well as the housing colonies and so on infrastructure you may say. And this is where high voltage underground cables are becoming a part of modern day civilization. And apart from power electronics guys, the best possible solutions to how to lay the power cables in the soil mass can be given by the geotechnical engineers. There were many projects which I have been dealing with in the country and abroad where these type of situations were dealt with by us and our research group. And then I will show you some of the case studies where how these situations were you know answered. Different types of roads, pipelines, structures in the cold regions they require the concepts of thermal properties of the soils. Particularly in the cold regions where the freezing and thawing is an absolute problem. People are talking about insulation of the geomaterials so that the structures or the infrastructure which is coming on the top of these type of deposits does not get distressed when freezing and thawing actions take place. The most important of these type of infrastructures would be the air strips in the cold regions. And I am sure you must have realized that including India rest of the world is also facing a severe problem of creating air strips in the regions which are extremely cold where the freezing thawing action is extremely important and very critical for the safety of the infrastructure. Then comes the agri and aquaculture fields and the solar ponds. You will be surprised to know that the design of the solar ponds is based on the thermal properties of the geomaterials because the whole idea is to grow the aquaculture or agriculture and unless the proper temperatures are maintained within the ponds you cannot grow shrimps, you cannot grow lobsters and whatever. So this is what the demand is in present day society. So when you design these type of ponds the thermal properties of the geomaterials particularly the foundations of the ponds becomes very, very important. They should not be allowing heat migration taking place through them to maintain the optimum temperature for the culture of aquatic life. Then ground improvement techniques including the soil heating and freezing which requires a lot of concepts of the thermal properties of the geomaterials. I think I have cited some examples also when you are working in highly fractured rock mass and when the tunneling is being done where the highly fractured rock mass might allow the groundwater table to get activated and the seepage occurring into the tunnel shoots. This is where the ground improvement can be done by freezing of the geomaterials, the rocks particularly. Brick making is a beautiful example of you know how the clays or the soils react to thermal fields. And if you go to the history and particularly the stories of the world war II, there was a time when the airstrips were made overnight by heating the soil from the top and making sure that the influence zone of the heater which is heating the surface is about 300 to 600 mm. So, this is how you can cast the roads under in situ conditions. Different types of thermo active structures which people are talking about these days require thermal properties of geomaterials particularly energy conservation schemes. So, thermal piles are good example of heat exchangers which are being designed. This is also a good example of you know why somebody should be studying the thermal properties of geomaterials. Transmission of the hot flades, most of the time transmission is done underground. So, this is a similar situation as of the power cables where you are trying to convey the power electric current and in this case this could be air conditioning duct or there could be some chemicals which are either going into the industry or coming out of the industry under all circumstances you want to minimize the heat losses, all right. A good example would be pipelines also where you might have to do thermal insulation of the pipelines so that the cavitation does not occur in the pipeline. I hope you know what is cavitation. So, imagine a situation where you are pumping hydrocarbons through the pipelines and these pipelines are passing through very high climatic conditions, very extreme climatic conditions, extreme temperatures like you know deserts Rajasthan, parts of Rajasthan and so on. So, the chances are that the hydrocarbon might get you know vaporized because of extremely high temperatures and hence the cavitation may occur and once the cavitation occurs you cannot convey the fluids further. So, the subject is becoming very important and very relevant to the contemporary geotechnologists and I hope you know the importance of you know infrastructure which is being done for sustaining the society, the present day society. Another interesting example is the heat loss from the basement of the buildings, mostly cold storages which are designed or which are constructed you know to save the cost of the air conditioning the best thing would be to isolate these type of structures from the environment and hence the basements have to be insulated. This is also valid for the hydrocarbon tanks which are installed in the tank forms very close to the coastal areas where the import, export of the crude oil takes place or different type of chemicals occur. So, under those circumstances also you would like to make a foundation system which is thermally insulated. So, I hope it is clear to you that there are a lot of applications of why somebody should be studying the thermal properties of geomaterials. It is a very contemporary subject. Now, there are three properties which I would like to find out or define for the geomaterials and these are thermal resistivity, thermal conductivity which are related to each other in the inverse form. So, thermal resistivity is RT and inverse of this is thermal conductivity k. Second is the thermal diffusivity, how easily the heat gets diffused from one point to another point. If you remember when we were analyzing the you know the energy fluxes and this is where the second order differential equation which I was talking about you know we were discussing about you know the similarity between the diffusion coefficients and one example I had given to you was the similarity between alpha or Cv the coefficient of consolidation. So, thermal diffusivity is a similar sort of a term which indicates how easily the heat flux can diffuse from one point to another point in the geomaterial. Accumulation of heat is not a good idea, why? Because if the accumulation of the heat flux takes place the temperature of the geomaterials will rise and once the temperature rises the chances are that the moisture will be lost coupled phenomena, heating induced moisture migration and which will ultimately result into the cracking of the soil. So, this is what we will be discussing subsequently after studying the thermal properties of geomaterials. The third parameter is specific heat of geomaterials defined as Cp. In your 10 plus 2 physics I am sure you must have done this. If you want to know what is the heat discharge Q, so normally what you do is m into Cp delta theta is it not, where m is the mass of the material Cp is this specific heat multiplied by change in temperature and that is the heat flux which is either going into the system or coming out of the system. I am sure you will realize that there is no conventional tool or equipment which is available in the market which can be utilized for determining KRT alpha and Cp. So, our research group was you know quite active in this context since the early 21st century and we have been doing lot of work in this area and in the process we came out with design of instruments and design of you know methodologies followed by the experimental work. This is a big challenge to determine these properties like thermal resistivity and thermal diffusivity and specific heat and in today's discussion I will give you some idea about how these properties can be obtained by simple instrumentation and which has been done by my research scholars and I am going to present this to you today. There is a relationship between these parameters that is the thermal resistivity RT, rho is the density of the soil mass or the media, alpha is the diffusivity and specific heat is Cp. So, Cp is RT into alpha into density inverse of that. So, if you know two parameters, the third one can be obtained because density of the soil media can be obtained very easily. So, if density is known still I have three unknowns. So, out of the three unknowns I have to obtain at least two parameters to obtain the third one. So, normally the practice is that by conducting heat migration experiments we obtain RT directly which can be obtained inverse of RT will be the conductivity which can be obtained and then diffusivity is obtained. If you want to find out specific heat either you obtain this mathematically or there are some other equipments like if you remember we have talked about differential scanning calorimeter DSC. So, that can be utilized to obtain the specific heat of the material or you can do simple calorimetric experiments which you might have done in your class 10th and 10 plus 2. If you remember you take some amount of the material and then heat it in a calorimeter and then find out how much time is required for the temperature to sustain itself and so on. It is so interesting to see that all these conductivities can be related to each other and good example is that hydraulic conductivity can be related to the thermal conductivity. So, this concept has been utilized by us in determining the hydraulic conductivity of unsaturated soils because as you must be aware of that is very difficult to create unsaturated profile of the soil number one. Number two there are no instruments which can give you the unsaturated hydraulic conductivity of the geomaterials. So, under these circumstances the best thing would be if I heat the soil mass slowly and if I create a unsaturated soil state or unsaturated geomaterial state by allowing the moisture to migrate out of the sample. This is how I am creating a unsaturated state of the material and then if I observe how the moisture front moves out of the sample over a given period of time I can compute hydraulic conductivity. So, this is an intricate work I have guided two PhDs and the best one I would be saying is of Dr. Hanumanthra who is a faculty member at IIT Bhuvaneshwar now he is a pioneer in this area and he did lot of work related to unsaturated hydraulic conductivity determination of the soils by heating the slow heating of the samples. What you have to make sure is when you are applying thermal flux to the soil samples or the geomaterials they should not crack and the cracking would occur because of loss of moisture, fine. So, this is an interesting philosophy which has already been exhibited to be working alright by our research group and there are lot of papers which are available in the repositories. So, coming to the factors influencing thermal properties of geomaterials with a big series of the parameters which influence thermal properties number one is the type of the soil definitely the texture of the soil plays an important role. Then is the moisture content because I am sure you must be exposed to this fact that heat migration through air is going to be less as compared to heat migration through the liquid phase is this correct or not water is a better conductor of heat as compared to air. So, moisture content in the voids plays a very important role. Imagine a situation where the pores are filled up with air only and if you heat the system in second situation there could be a partially saturated soils where you have some air some amount of moisture and then you heat it and the third situation could be I have the pores which are fully filled up with water saturated soils alright. So, heat conduction is going to be much faster in the saturated state of the material as compared to the dry state of the material. Then comes the distribution and size of the grains because this has something to do with the density of the material. So, uniformly distributed soils will create a dense matrix this is a well known fact. So, if particle to particle contact is better the heat conduction is going to be good as compared to the situation where particle to particle contact is not good fine. So, distribution and size of the grains indirectly controls the density and this density is directly controlling the heat migration through the geometricals. So, more the density the resistivity is going to be less. So, density of the soil plays an important role temperature and pressure I am sure you must have come across this concept when you are doing your 10 plus 2 Phyrix that you take a resistor and pass a current through it and when the temperatures are increased what happens to resistance the resistance also increases and that is the reason we are quite bothered about designing the power cables. So, imagine the power cables are buried in the soils and soils exhibit very low thermal conductivity or very low thermal diffusivity. So, what is going to happen when you pass the current through the cables the soil mass in the vicinity of the power cable attains very high temperature and when the soil mass attains very high temperature what is going to happen to the cable itself the resistance will increase and if the resistance increase what happens to the power I square times R clear. So, first of all there will be losses of the current you cannot pass the current because of very high resistance. So, imagine from one city to another city if you are trying to transmit current because of elevated temperatures of the soil or less diffusivity of the current in the soil mass the temperatures of the cables will rise they may get burnt clear. So, this is a very trivial situation or even if they do not get burnt the current carrying capacity which is known as MPCT of the cable wires or the cables decreases we call it as MPCT all right. So, the current carrying capacity gets affected. So, it is a very intricate subject I am sure you must be realizing and what is the role played by the geotechnical engineers I am trying to emphasize all the time presence of contaminants depends what type of contaminants are present in the geomaterials all right in what phase this could be liquid this could be solid this could be gaseous phase and they would have their own influence this concept or this factor has not been investigated much until now requires lot of understanding and lot of you know experimentation first of all to put things together and then to frame the thumb rules method of measurements it depends upon what type of measurement method you are trying to use or which is being employed for conducting these studies I will be talking about different methods also another interesting thing is the way we are utilizing these properties that is the thermal resistivity diffusivity and specific heat I want to utilize them to create a classification scheme of the soils and the beauty is that this type of a classification scheme will include physical, chemical, mineralogical, chemical aspects associated with the geomaterials I hope you can understand this. So, depending upon the minerals whether the minerals are acting as insulators or good conductor of heat clear so that is the fundamental nature of the mineral a good classification system can be created. So, let me talk about the transient method which is what we have practiced much in our laboratory and which turns out to be a quite a decent method to find out the thermal properties of geomaterials transient is something which is short lift momentary. So, what we do is we apply a heat pulse of very small intensity for a very short duration to the geomaterials and the idea is simple we do not want any distortions in geomaterials to occur fine distortions first thing is moisture content second thing is if the minerals have their inherent thermal expansion coefficient I hope now you can realize where I am heading to because of the expansion when they are exposed to high temperatures what will happen there is a distortion in the matrix which is going to occur. So, that means under these circumstances the initial state of the material is not going to be same as the final state of the material. So, you will be measuring the properties of a different state of the material. So, these are the issues which have you know helped people to talk about the transient methods where low intensity heat flux is applied for a short duration 1 minute 2 minute maximum and idea is to measure how this heat pulse migrates into the geomaterials. So, this type of a probe was developed by my student in 2000 on in fact before that 1995 I would say one Mr. Gangadhar Rao was there he created this thermal probe he was the person who was working in this the first project which I handled for cable corporation of India that time you know there was a big supply of cables which was being done and the installation was being done for different industrial applications and people were clueless that how to find out the thermal properties of soils. So, we were the first in the country and maybe it is a significant part of the world to tackle this problem. So, what you see over here is that this is a copper tube of about 95 mm long it is a hollow tube and then we got this fabricated we put a nichrome resistance wire inside and we fix it at the bottom and then we put a thermocouple inside the probe all right this is a T type thermocouple and the probe is ready. Now, if you buy this instrument this will not be costing you less than few lakhs the commercial organs of these instruments will cost you about 7 to 8 lakhs these are available in the market unfortunately we could not patent and we could not fabricate this things at that time. For better supply of the heat which gets generated through this nichrome wire when you connect this to the power what we do is we fill up the space in the tube with a something known as you know heat source sink fluid this is a oil of high thermal conductivity. So, what the whole idea is that you replace the air which is inside the tube with the heat sink fluid. So, this system becomes a monolith and what you are observing is that the other end is tapered. So, I can insert it into the ground very easily just by damping it clear. And then this thermocouple gives me what is the temperature of the thermal probe this is a copper tube the surface is going to be an isotherm the moment I put this whole thing in the soil mass the temperature of the copper tube and the soil mass attains equilibration and that is what is measured over a period of time. These are the thermocouple leads which were used you know. So, the thermocouple is grounded at the junction at the bottom most point there is stainless steel tube of 1.2 mm diameter and this is the body of the insulated T type thermocouple all these things was done in house at that time.