 So, now moving on to what type of structures which can be created by using sheet piles. The first structure which we will create is a cantilever sheet pile alright, because as I described earlier, most of these piles are acting like a cantilever. This is the anchorage and this is the pre portion. So, how this looks like as we discussed earlier, you take a element of the soil, element of the sheet pile, insert it into the soil, this is the ground surface and this becomes the, we call it as a dredged level, because most of the time sheet piles will be inserted into the existing ground by removing this portion of the soil. So, this becomes the dredged level, this is the ground surface and this is the dredged or excavated level. So, this is a simple cantilever sheet pile alright, you are retaining a backfill by using a sheet pile. As I said these systems are not for permanent construction, this is just for temporary constructions up to a limited height. I can complicate the stability problem by introducing the concept of seepage here, which you studied in soil mechanics first course where we studied seepage into the porous media separately, got this point. So, suppose if I say this is the water table, now what is going to happen? The concept of seepage will come in the picture, these flow lines, this you have studied already and then you can do the equipotential lines also. So, basically now you are realizing that what we are doing, we are heading towards totality of the situation and the problem. So, immediately a simple problem which was basically a soil structure interaction has been converted into a soil structure water interaction problem. So, you need not to worry much, what water is going to do, it is going to cause pressure on the sheet pile, clear. We know the port of pressures at each and every point of the sheet pile, we can compute the port of pressure in the form of force, we can include that in the stability analysis as a force component, fine. You remember another problem which we had done in C323, there is a ground surface and the question was how deep I can go without the soil mass capes in. So, you have this sheet pile assembly and then I will do sequential excavation. So, this is gone, this is gone and the question is how deep I can go so that this is the water table, water tables could be different on either side. So that the soil here does not cave in. So, we use the concept of effective stresses over here, you remember. So, we computed the port of pressures by using the flow nets and the moment you have port of pressure you can find out the effective stresses and the moment effective stresses tend to 0, that is the limiting conditions required for D. That means this problem becomes a very interesting problem, D is going to be a function of how many parameters, the porosity which is inclusive of wide ratio, R D of the soil, gamma D of the soil, the type of the soil, hydraulic head, hydraulic gradient, delta H which is going to cause the instability in the trench, correct and length of the flow path. Apart from this anything else, now if you analyze this system in totality we have to talk about the pressures which are going to act on this so that means now this problem becomes this depth of excavation plus D. So, I have one more unknown coming over here which is in the form of D, where D is the depth of embedment. So, so far we had analyzed this system for seepage induced instability without taking into account the earth pressures which are coming on the system. Now we are doing both together, okay. So, we have to use another term as factor of safety for the first time I am introducing this concept and before this we just talked about factor of safety when we are discussing the Mohr-Coulomb envelope that how would you define the factor of safety associated with the material in terms of its shear strength, fine. You can play with this function and you can solve this. A lot of things have been conveyed in one figure, but now I am real I am sure you must be realizing that from theory we are talking about the practice. Now look at this how this problems can be amplified or amplified in the sense suppose if height of retention is more you know I am not very happy with whatever edge I have created or if height of retention happens to be more than 5 to 7 meters what I should be doing the simple logic says put an anchor. So, this becomes an anchored bulkhead. So, this becomes the second type of the sheet pile, all right where what we do is in this system we will introduce an anchor. So, this is what is known as an anchor or a tie rod and tie rod when connected to a anchorage system. So, truly spring this is not an anchor this is an anchor rod or tie rod this is connected to an anchor this is the anchor block. So, this becomes another interesting design problem what should be the length of the tie rod from the free head at what depth I should be using this tie rod what should be the dimension of the anchor block how many number of tie rods are required all right and what should be the spacing. So, now we are realizing this becoming more intricate design problem. So, in a 3D system this is how it will look like ok and this is the drag level this is the ground surface and all these tie rods are going to be like this of certain length centre to centre spacing yes you have done this type of analysis instruction also Perlin stresses is it not a design of Perlin correct is very similar. Now, this phase is holding the earth pressure which is coming from left hand side and trying to deflect the ball on the right hand side this is the problem statement. So, a simple situation like this has been transformed to anchored bulkhead where these are the tie rods which have been used these tie rods could be made up of steel these could be wires all right this could be a wooden block this could be a concrete block this could be a steel rod or whatever sometimes when you see how this rock fall protection systems are being installed ok typical example is Bombay Pune Express highway. So, if this is a slope or a rock mass which is vulnerable to failure and by cutting you have made it let us say very steep ok and now you want to stabilize it. So, the best way would be to create a trench over here and put a running anchor and then this anchor is holding the wire mesh and this wire mesh is this is what is known as high energy panels and they are fitted with anchors soil nails. So, these blocks have very different applications basically they provide anchorage to the entire thing the self weight of this system made up of steel itself is quite high. So, these anchorage systems are very useful all right this is a similarity. The third one could be a braced excavation struts by using struts. So, we have the ground surface and then we are installing two piles excavate it this is another in another way what we have done is we are supporting the excavated slopes so that we can go much deeper and then install the struts over here these are also known as bracing these are known as bracing or struts what is the job their job is first of all if you would not have provided the sheet pile the whole excavation would have kept in all right. Now doing this excavation and providing these sheet piles you are stopping it but even if the depths are too high or the soils have different conditions of drainage or let us say you know type of material which was retaining still they may came in or they may fail. So, for added precaution the more you go deeper they put struts the question is whether these are compression elements or tension elements you have to think carefully check it out all right I know many of you are very good structural engineers here draw the free body diagram and then you will get the answer what this system is going to supposed to do. So, what is the answer these are all tension members they say paradox the soil mass along the wall is pushing this system. So, this system has to apply a tension to support that so all these are tension elements they are not compression elements right. So, this becomes a typical braced excavation we will be discussing a bit about this in C330 metros are mostly done by using this type of system you might have to have struts if you go to a metro station the way it is being done you are excavating out the soil cutting out the rock and then you want to support the you know walls of the rocks or the soil mass and there you require struts this could be columns also many times you use the pillars and to support it then there is another structure which is made up of sheet piles this is what I talked about the cofferdams ok I have already discussed this there could be cellular cofferdams also depending upon the requirement I might be having a cofferdam over here another cofferdam over here for the ease of construction it is very difficult to seal the entire soil mass against seepage alright. So, imagine if you are constructing the sheet piles it is not so easy to avoid leakage of water and when leakage of water takes place or seepage takes place I hope you can realize the points which are in the soil mass may also get washed out these type of failures are very common in coastal regions and I have dealt with several cases where we have to show that the fines have washed out and hence the collapses occurred. So, whatever structures standing over here if the cavity formation occurs the collapse may occur in the due course of time. So, if you want to avoid these type of situations the first thing is you create either piles or the cofferdams and then connect them in this manner it becomes a watertight compartment alright. So, these are techniques which you need not worry about there are experts who can do this expert execution agencies which may give you a completely watertight system and hence no washing of the fines is going to take place. There is another category which is known as diaphragms diaphragm walls. So, these are very thin structures made up of sheet piles alright RCC also and the job is to avoid migration of fines they also look like this the diaphragm wall will look like this they are interconnected and so on made up of the sheet piles temporary supports. So, anything which is very thin and you want to retain it diaphragm walls are being used in the practice. So, in today's discussion what I have done is I have given you a brief background about the sheet piles their types how to use them for construction purpose different examples of what type of structures can be created and the philosophy behind using the sheet piles from next lecture onwards I will go into the analysis part of it. Watch more videos to understand how these systems are created. Thank you.