 We have been talking about the material characterization and particularly the chemical characterization and this is where I will cite one example, a case study which was done by us a few years back followed by the corrosion potential which is a very important topic in today's world and lot of industries where the piping and the underground or buried structures are installed require studies to be conducted in this context. Of course after this I will be switching over to this option-disoption and followed by thermal, electrical and magnetic characterization. So to begin with the case study normally when you come across these type of situations the questions you have to ask yourself are what are the types of contaminants which you are going to deal with. Because depending upon the contaminants type you will be having a strategy in your mind or you will be evolving a strategy which would help you in understanding what is the extent of contamination of geomaterials and how to remediate that. In other words the first question which comes to mind is whether these contaminants are organic in nature or they are inorganic in nature and this question is asked because of the obvious reasons that the detection tools or the equipment which we are going to use or the strategy which we are going to follow would depend upon the basic nature of the contaminants. So we have discussed about different techniques in the previous lecture and what we can reiterate is that normally CHNS analyzer is required. This is the carbon hydrogen, nitrogen and sulfur analyzer is required, this is an equipment which helps you in finding out the CHNS components of the geomaterials and then what type of alterations these components are going through or the elements are going through in the process of getting contamination of soils that can be detected and quantified. FTIR is the Fourier Transform Infrared Spectroscopy, this I have talked about in the previous lecture and followed by GCMS that is gas chromatography with mass spectroscopy and of course ICE, ICPE, AES and AAS. So these are the tools which are normally used. So just to show you how the results would look like these are typical results which convey from the FTIR analysis which you get what is the extent of contamination of the soils. So S1 to S11 are different course of the soils depending upon either the time or the locations from where the samples have been withdrawn and on y-axis we have percentage transmittance and on the x-axis we have the wavelength. I hope you understand from the basic background of your chemistry that wavelength is associated with the bonding between the two elements. So what you are observing here is a typical pattern which shows what type of bonding and the nature of the bonding is available in the soil mass or the geomaterials. So for that matter here I have written let us say silica oxygen stretching and here the silica oxygen is in the bending. So this is a sort of a bond and if you remember our preliminary discussion the whole trick is about how to break these bonds so that the soils can be decontaminated. So FTIR happens to be a good tool where we can at least qualitatively we can identify the presence of foreign elements particularly contaminants in geomaterials. The second analysis is the results of the GCMS which I am showing here. So as I said this is the gas chromatograph mass spectroscopy. Depending upon the retention time I can identify the compound and we can quantify by using the MS component associated with GCMS what is the extent of intensity. Intensity can be correlated with the percentage of these compounds which are present in the system. So there is a big list of compound which you can identify based upon their fingerprint in the geomaterials. These type of analysis are all the part of forensic examination of the geomaterials nowadays and then comes once you have identified what is the qualitative contamination present in the system or quantitative contamination present in the system you can plan the remediation techniques. So some of the remediation techniques which I am going to list over here are number one is the air purging. I can purge the air inside the soil mass. This is what I was talking about in the previous lecture also where the compressed air or the compressed oxygen is pumped into the geomaterials to oxidize the contamination which are present. This could be a very good solution for the soils which are oil contaminated or hydrocarbon contaminated where you can break the bond between the soil mass or the geomaterial and the hydrocarbons by purging the air. The second one is electro remediation, a slightly complicated technique where with the help of electric field you can decontaminate the soils. Electrokinetic process is one of the processes, another process could be electro osmosis. So these are two processes which people have tried in the past. Of course these methods have their limitations and strengths which you should study by going through the papers which are available in the literature and sometimes these techniques become very difficult to you know employ on the site because of the cost of the paraphernalia or maybe like in electro remediation method this the biggest question would be if you are passing a huge amount of current or the voltage it might be unsafe for the people who are working over there. There is another interesting technique by which you can do the remediation of geomaterial which is bioremediation and this is the upcoming area where lot of research is being done and I would suggest all of you to go through the literature particularly on Google there are lot of papers which are available on these techniques, their utilization, how to employ them, what are the limitations, what are the strengths and so on and where we are as a nation or internationally. Another method which can be tried I think some of you talked about this phytoremediation. So this is also a very interesting technique of decontamination of the soil. Now one thing you should realize over here is that it is a chicken egg story where the soil gets contaminated first or the groundwater gets contaminated first this has to be decided because many times it so happens the soil becomes contaminated first and then because of the leaching of these unwanted contaminants or species the groundwater table becomes contaminated. However the reverse process is also possible because groundwater table is a part of the geomaterial system and in case there is a flux of contaminants which is present in the groundwater or the pore solution the chances are that the geomaterials will be contaminated. So when we do remediation techniques both the aspects are kept in mind that is the contamination of the soil as well as the groundwater or vice versa. The only thing would be taking out sample of the groundwater will be easy and this can be directly analyzed by using ICPMS or GCMS however when you are dealing with the soil phase of contamination or the solid phase of the contamination then you have to extract the solution and that solution has to be analyzed by using different techniques. I will start now a discussion on corrosion potential of soils and as I said some preface I had given you in the previous lecture why this subject is becoming more important in the realm of geotechnical engineering. Most of the foundations and underground structures are exposed to the environment particularly sub surface and this is where the chances of contamination of the porous media are very very high and once you have contamination which is present in the soils or the groundwater it may so happen that the underground structures might be under threat as far as the safety of the structural health is concerned. Now why these studies are becoming very important for geotechnical engineers because metal corrosion has become very important thing in undisturbed soils particularly when we compact the soils when we talk about the soils which are under in situ conditions and we insert lot of elements like foundations or sheet piles or the piles in the ground and you would like to see what really happens to the cover of these elements in the form of the concrete or it could be a metal and the reinforcement which is lying inside. As I said the buried pipelines and the backfill soils have to be characterized properly when you are using them for different industrial applications. So industry is facing two problems number one is how to convey liquids underground the overhead conveyance is extremely hazardous and difficult and second thing is that if I have to lay the pipelines I have to backfill the soil to compact it is it not. So from where this type of soils will come which are supposed to be the best soils or the geomaterials which would be safe for the health of the buried systems. So I hope you can realize that this is directly coming into the realm of geotechnical engineering and here the pretext is that soils change their chemical and physical nature over a period of time and depending upon the climate. So these issues have been ignored earlier and when I say climate and time I hope the connotation you can understand is this is because of the bacterial activity. So the bacteria which harps in the soils gets activated or may become supercritical or may become dormant depending upon the environmental conditions. So these are the situations which are bothering geotechnical engineers when we talk about the pipelines you know this is the pitting sort of a of a system and this is the corrosion. So excessive pitting might lead to the corrosion of the metals. I have come across some of the cases where there was a litigation going on between the client and the contractor where you know big pipelines were installed and I hope you understand that the pipelines are extremely expensive utility items and it so happened that by the time the pipelines were charged, charged in the sense when they were open for fluid flow people realize that the conveyance of the liquid was 0 alright. So when they opened the walls they realized that nothing came out from that particular pipeline and then the litigation started and then the enquiries started and what we realize is that the entire pipeline was eaten up by the soil and this is one of the piece of the pipeline which I collected and I brought to the laboratory to do further analysis of what went wrong. So these issues are becoming very very trivial and very critical in the contemporary society. I hope this connotation is clear when you have disturbed soils, the densities are going to be different as compared to the density state of the undisturbed material and hence the air permeability and water permeability in the form of rains is going to be different and once you have ingress of fluids in the buried systems this could be problematic because wherever oxygen is present the tendency of the oxygen would be to oxidize the things so this is the answer to your question. So permeability gets affected, strength gets affected, durability gets affected and at the micro level if you really enlarge this issue hope you will realize that the question to be considered is that how microbial activity will grow in less compacted soil or more compacted soil and this is where we talk about the concept of aerobic and aerobic bacterial activity. So compacted soil acts as a barrier for the air to communicate with or the environment to communicate with the buried structure. I hope these logics will help you in understanding why this subject is becoming important. Yes please. In the past we have used wooden piles for this purpose so nowadays is it possible to use such. So you are talking about the monuments where the wooden pile has been used and I am sure that you must have realized that it was made sure by the engineers of that era that these wooden piles will not get oxidized they do not get exposed to air that means most of the time the system remains under so much condition. So if you go to our most of the monuments where you have bowdies we call them in in the end Urdu I do not know what you call them in your language the there are several structures monuments where two three stories remain always submerged in water. So when you cut off supply of oxygen the system would not get oxidized and what is the classic example of this wood under wet form which is pretreated is always much more durable than concrete even so this is the answer to your question ok.