 So, so far in this course I have discussed in details about the shear strength determination of different types of soils. We have talked about direct shear test, wind shear test, triaxial test of different types from direct shear test, what parameters we get, we have analyzed them. From triaxial test, what parameters we get, we have analyzed them in details. We have discussed about the pore-water pressures, how do they develop, what is the importance of pore-water pressure parameters and how would you utilize these parameters including the shear strength parameters to characterize the soils of different types as an engineering material, how to do engineering on these materials. And then we switch it over to earth pressure theory, alright. So, these were the basics of the geotechnical engineering 2 course or these were the basics of the materials like soils of different types. And what we have learned so far is how to understand their basic characteristics, how do they perform under different types of drainage conditions and loading conditions. Once we have studied all these things, the issue is where you are going to apply this knowledge. So, one part of the application of shear strength theory was earth pressure theory which we discussed quite in details and there we talked about different types of retaining walls, how earth pressure gets mobilized on them, we talked about mostly back fills with granular material and then a little bit on how to retain cohesive soil mass as a backfill material with a caution that cohesive material should not be utilized as a backfill material. So, we did all these analysis. Now, I am switching over from the basic concepts to the application part of geotechnical engineering 2 or you may say this is how the practicing engineers would be using the concepts which have been laid down for understanding and basic characterization of the soil mass, engineering characterization, alright. So, let me introduce now the concept of sheet piles and these are sheet pile walls. Now, you must have noticed that in the practice of geotechnical engineering there are several situations where right of way or the right of property or the property line becomes a very big issue. So, so far what we have done is we have studied retaining walls. These were mostly gravity retaining walls, why gravity? Because the cross sections are very thick, the self weight itself was good enough to negotiate with the pressures which are going to come on the walls. So, what we did is we took heavy sections, you know, this is how we design a Re wall or retaining wall on which the earth pressure is coming. So, many times as I said it is not possible to afford the luxury of space, okay. So, what would you like to do? But still you want to create a retention of the geomaterial. So, under these circumstances what we can do is we can switch over from gravity retaining walls which are basically rigid structures, flexible structures, alright. And these flexible structures are also capable of retaining soil for retention of earth or soil, okay. This could also be water, this could also be gas or any sort of liquid, chemicals. So, the, you know, tanks which you see big, big tanks where the petroleum is stored, they are also made up of thin sheets of steel, truly speaking each element itself behaves like a sheet pile. So, when we talk about the flexible structures by definition, opposite to a rigid gravity structure where the base widths are extremely high, alright, very, very high, these structures have very thin cross sections. So, in the process I can save this much amount of the space which is required if I consider this as a half of the retaining wall for construction purpose. So, a thumb rule says if the height of the retaining wall is about H, the base width would be approximately 0.7 H. Now, I think you can realize if you are creating a 10 meter high wall for retaining the soil mass, if you remember the backfill we have stored over here or we have. So, this was the ground level, this is the backfill material, so suppose if H is equal to 10 meters, the base width of the or the base width would be about 7 meters, so everywhere you cannot afford this type of a system, gravity system apart from it requires too much volume of the concrete, masonry or any compacted material, alright. So, under these circumstances we go for a flexible structure for retention of earth, soil mass, water, gas, it could be any food grain also for that matter, why not, so depending upon what is that you are storing a sheet pile system can be designed. So, as a geotechnical engineer most of the time we deal with retention of earth, soil mass, water with very thin cross sections as the elements, okay, so suppose if somebody asked you a question, there is a ground surface like this, alright and this fellow wants to construct a form house which is elevated, so he says that I do not want to live over here, I want a sort of a some height to be created over here, alright, so basically he wants to create or she wants to create a facility over here, so the first question is how would you do this? On piece of paper I could draw it very easily, but how would you do in the practice? So the best way to do in the practice is take these flexible structures which are retaining the material, which are thin in cross sections and you insert them over here and then what I can do is, I can fill up on the right hand side, soil mass compacted, okay, by controlled compaction you have studied how to check the compaction of the soil in layers, make it as a platform, so this platform once it gets created of height h becomes a sheet pile wall because this happens to be a sheet pile, look at the beauty, I could have done the same thing by creating a retaining wall over here, alright, so if I would have done a retaining wall here, how much space would have been eaten up so much, correct, so I get the same advantage of creating a retained soil mass on which I can create a facility just by using thin sections and hence the space can be optimized. Now I can realize that what is the application of this type of a construction in metros where the space is a luxury, it is very expensive, getting materials to make a retention system is extremely difficult, this idea seems to be workable and I am sure the concepts of mechanics will tell you that this is a system which is very easy to analyze as well, so what you are doing is, you are using the concept of embedment of an element into the soil mass, so this is the soil mass and trying to retain a bulkhead, in technical terms this is defined as bulkhead, what is bulkhead, bulk is the bulk of the material, volume of the material and head is that you have created certain height, alright, so this becomes a bulkhead, so in retaining walls we used to use the word bulk, sorry back fills, alright, which is retained by the retaining wall, when we adopt sheet pile the terminology is bulkhead or the soil mass which is being filled up over here, this could be water also, okay, so this is one of the facilities which I have created, I have created a elevated bulkhead for developing a property, there could be a different situation also, there could be a situation where I want to create a basement let us say, there is city like Bombay, you know most of the infrastructure requires parking lots or some facilities, underground facilities let us say, a cancer treatment facility in a hospital where you do not want to expose the x-rays or different type of isotopes which you are using on the patients to the atmosphere, so these type of facilities are normally concealed, they are underground, alright, so suppose if I want to construct the underground system, I could have used the retaining wall also there, but then as I said these are the negative aspects, the best thing would be use the sheet pile and what can be done, I can start excavating over here, so if I start excavating okay, I can remove this soil mass and I can create a facility over here, so this material can be removed and in other words what I have done, I have created a underground facility, so this becomes an underground facility, this is okay which is nothing but a basement, so now you are realizing we are the master of the subject, we are trying to use the concepts in such a manner that I can create any structure, I can create any facility, if I remember the concepts of stress paths which we did after triaxial testing, how would use the concept of triaxial testing here, the stress paths, so go back to the basics, take a point at a depth of z and define the state of stress, I can do the same thing over here also, this point alright and I would like to find out the state of stress at point 1 and at point number 2, so if this is sigma v, sigma h, same thing is acting over here, sigma v, sigma h what is the difference between the two situations, in this case delta sigma v is greater than 0, loading case correct, now delta sigma h could be whatever, we have solved this type of problems, we have defined these stress paths for this condition, starting from a hydrostatic condition or from a different initial condition, if I construct a facility, I know how much is the height of this, I know the unit weight, I know what is the delta sigma v value, delta sigma h may be 0, it could be positive, it could be negative also depending upon how you are using this space, in this situation what is happening, when I am removing the material delta sigma v becomes negative, removal, remember we talked about these conditions in the stress paths okay, active earth pressure, passive earth pressure, loading and unloading, we had drawn this long back, so please go back and check those lectures again, so coming back to the point, this thin elements are becoming very useful for construction of infrastructure, mostly in soft soils, but please remember one thing, in case of soft soils these structures are not going to be permanent, they are only going to be temporary alright, so they are basically made for temporary retention of soil mass that to not of very big heights, not very large heights, so heights will be roughly 3 to 5 meters, not more than that, but they are very useful for granular materials and then we can design a system in such a manner that I can achieve the certain height, now you can realize intentionally, I did not talk about anything which is beneath the ground, but your concepts of engine mechanics and solid mechanics and basic structural engineering will tell you that this is what is going to give you the embedment and this embedment also mobilizes the moments, so if you now start putting the mechanics here, what you will realize is this portion which is hanging up the ground surface would have a tendency to deflect on the left hand side, why? Because the simple logic says that this is the bulkhead which I have created is going to be under active earth pressure condition, so it is going to apply active earth pressure, now we will further discuss this later, but anyway just for a quick discussion, the embedment is going to come from the resistance which is being offered by the soil mass on the left hand side, so the way I have shown an excavation if you do it like this, I am sure your retaining wall is going to fail. Now this is where we have to apply the concept of optimization of the excavation from the face of the retaining wall, that means there has to be a distance up to which this wall is going to be stable, that means this much of the soil mass which I have created is going to apply a passive earth pressure on the retaining wall, so truly speaking these flexible units which we have inserted into the ground for creating retention or creating excavation, they are known as sheet piles, why wall? Because these are the walls made up of the sheets and they run in several meters or hundreds of meters or tens of meters depending upon your requirement alright, so now you can visualize in the 3D, so these walls will be running up to certain length as far as the property line is concerned and what we are doing is we are utilizing the concept of active and passive earth pressures to analyze the system and of course the stress paths, because without stress paths we cannot compute the incremental changes in the active and passive earth pressures, so all these basic we have discussed in the class fine. Now what you require is the material property, the moment you know the C5 gamma drainage conditions, submergence conditions you can compute TAPP we have done enough analysis, the whole aim is to find out D so that I can say the total height of the wall is equal to H plus some factor you know let us say M times D, so this is some factor which we will be discussing later on alright, so these are basic concepts. Another example you might be doing you might have observed you know trenching operations for laying the pipelines, so this is the ground and normally these pipelines which are carrying water or hydrocarbons, petroleum they are normally buried up to a depth of 3.5 to 5 meters because of different reasons, number 1 to stop any type of burglary you know tapping of fluids unauthenticated, so suppose if I want to lay a pipeline over here how would I do this? You have to do a trenching operation, now trenching means you have to remove this material, we studied the concept of Z critical, you remember what is Z critical? The height of vertical cut in a C5 soil, so this is the unsupported height of vertical cut, so this we have studied already, the idea is if I am going beyond if Z is greater than ZCR what it corresponds to, this corresponds that you require some additional protection or support so that the trench remains stable, otherwise what will happen? Because of the earth pressure the trench will cave in, so this part also I am going to discuss in subsequent lectures where I will be talking about why bracing are required, why supports are required, what is the concept of slurry trenches and how to make the trenches stable, this will follow subsequent, there is another application of shear strength theory, so I am sure you must be realizing that there are a lot of applications of shear strength theory, so those of you who were under impression that this course is only conceptual or theoretical I am sure that you must be realizing now this is becoming more and more practical now, you can create a situation using the concepts which you have studied so far you can apply them and you can create a system infrastructure, so coming back to this point the best thing would be if this is the situation and you want to stop caving in what I should be doing, the best way would be if this is the ground surface you drive in 2 sheets sheet piles and this much and remove the soil mass and then find out where should I lay the pipeline or any utility for that matter, fibre optics cables, okay, underground pipelines, yeah drilling wells, so then you have to go much deeper, much much deeper, correct, so there could be any application for that matter, what you have to do is use the same concepts. Now, these piles or these flexible structures or the elements are made up of different types of materials, these the type of materials or the materials used could be material used for making sheet piles, so typically these are of stainless steel with a very sharp cutting edge, alright, so I will show you some videos today, so suppose if this is a thin element and if I make a very sharp cutting edge over here, this becomes a typical sheet pile, so what I have to do, keeping in view the stiffness of this element, I can push this element or the sheet pile inside the ground and this becomes a system like this, this is the art of installation of sheet piles and we are lucky that nowadays there are many specialized companies who are doing this work, design part you can take care of, analysis part you can take care of, execution part can be done by these companies, their expertise, these could be also made up of timber or wood, you must have seen in old constructions, people use wooden logs, a beautiful example of this would be dolphins, so dolphins are the type of structure which are used for offshore structures, alright, so stainless steel can be used, timber wood can be used, it could be a composite material also, nowadays we have so many types of composites, alright, they can be used, PVC can be used particularly for the landfills, a big problem with the landfills is you know if there is a landfill, lot of leachates come out, so leachates are the chemical species which drain out or which come out of the landfills because of the percolation or rainfall, okay, so suppose there is a facility like this and I do not want the leachates to spread out into the geoenvironment because most of the time there will be water table here, okay, so I hope you can realize the moment the leachates seep down into the soil mass, they will have a tendency to pollute the water table and the water table will be moving type, we have done this in hydraulic conductivity when you are discussing about the permeability of the soil mass, you know second 5th, 6th lecture of CE323 where you are talking about the hydraulic conductivity, so if you have a moving or flowing water table, this situation is going to be extremely hazardous, what should we do then? Contain the leachates migrating out, the simple example would be or simple solution would be insert sheet piles, okay and in plan how it is going to look like, it is going to look like a big space which you have created, alright, so I have created a confinement again by using small, small segments of the sheet pile, so you might be having the segments of let us say 2 to 3 meters wide and normally the length is, lengths are about 5 to 7 to 10 meters depending upon the material which you are using, I can put them together and I can create a cofferdam, is this part okay, so this is the design aspect, how we are going to use the basic elements and the concepts of geotechnical engineering to create a retention system, alright. So these type of joints are especially provided by the manufacturers and then you can easily create such type of systems which are almost watertight, so this is something which is latest in the geotechnical engineering application where the landfills are also being contained by using PVC sheet piles, okay, this becomes a typical cofferdam, so cofferdams are normally a type of a structure which are created for doing offshore related construction where you want to divert the flow of water or you want to create a space which is free of water, so suppose if there is a river which is flowing, alright, this is the river, this is the river bed and I want to construct a bridge over here, so for constructing the bridges we need the pairs also, these are supports, now where they are going to sit, they are going to sit somewhere over here, so this becomes the foundation, how do you create this foundation on blackboard or in piece of paper is very easy to do, but suppose if you are doing it in the real system where the soil is somewhere here let us say, it could be rock also, what we will do is we will create a copper facility somewhere like this, so it resembles the situation what I have created over here, so once you create a space, drain out the water from here by using pumping or say pump out the water and then this becomes a space where you can work, so most of the bridges in the terrain where rivers are flowing they are constructed like this by creating a copper dam, diversion of water, so I am diverting the water, creating a space which is free of water and I can work over there, so I am sure you must be realizing there is a lot of application of simple concepts of geotechnical engineering, you know starting from this to that end, so depending upon the materials which are used for making sheet piles, their design will get changed, their cross sections will be different, the methodology of installation would be different, so truly speaking sheet piles are classified based on what is the function they are going to perform, all right, retention of what, different types of materials, okay, so this is based on what is that you are trying to retain, this is the classification based on the type of material which is used, all right, you must have noticed that in villages particularly in parts of Rajasthan and other areas where stone is freely available what they do, they make slabs of stones and they insert them into the ground, so this could be made up of stones also, stones, slabs, all right, big rock mass they will cut in small pieces where they become slabs and these slabs are inserted into the soil mass, so I think this is what the basics are, it could be concrete also, yes very right, so this could be made up of concrete also, yes, so here you can put one more category as concrete, true, thank you.