 So, last class I have discussed about the tension pile and the pile subjected to lateral loads. Now, when the structure which heavily loaded, then we have to go for another type of deep foundation that is called well foundation. So, that is used for a heavily loaded structure like bridge foundation, where we generally use this well foundation. So, today's class I will discuss about various components of well foundation and then how to determine the depth of well foundation. So, now first what are the different types of well foundation as I mentioned that this is used for heavily loaded structure. So, and then what are the different types of well foundation. So, depending upon that construction methodology there are the different type of type of well foundation. So, first we will go so for that is well foundation. Now, first types of well, now first type that is called open cation or open well. Now, in this type that this is our existing bed level below any river. Now, here this one is the water level. So, this is water level, this is the existing base of the water body or the river and then open well the top and bottom is open during construction. So, that means here open well is allowed to sink into the water and this is another and then this portion is filled with concrete. So, that means when it is open type of well that here top and bottom portion is open during construction. That means during construction this top portion this is the top and this is the bottom portion. So, this two portion are open during construction and then this can be circular type and this can be rectangular type also and the process of sinking is continue till the reach the required depth. So, that means this process when it is sink sink into the water. So, it is continue till the required depth is reached. Now, once the required depth is reached then the bottom portion is filled with concrete. So, this when the required depth is reached this bottom portion is filled with concrete and then the ship this is the water portion and the shaft which are filled with sand. Now, once that means during the construction this top portion and the bottom portion are open. Once it is reached at the ground surface or the required depth then bottom portion is filled with concrete and the shaft is filled with sand. Now, advantage of this type of open well that the it can be constructed up to any depth or the up to the required depth and with a relatively low cost condition. So, and the limitation or disadvantage of this open well is the if the boulder deposit is there if the this ground surface or this bottom of the water body is there is boulder deposit represent then this is very difficult to process or progress the construction of this type of well. And then very slow this is this deposit this is very slow construction and concrete seal is done under the water. So, that means once it is reached in the bottom then the concrete sealing is done under the water which is not very effective and that is the advantage and the disadvantage of this open well or open cache. So, next type of the well is that is called box well or floating cache. So, this is second type of well foundation. So, here again if this is water surface and this is the well and this is the ground of the water body this is top bottom. So, in case of first case where the top and bottom both are remain open during the construction, but in this type of well the top is open, but the bottom is closed during construction. So, this is the closed bottom and this is the open top. So, that means this type of well the top open at top and closed at bottom. So, so this is cast in land. So, that means before this is this is as it is closed during the first case the bottom was sealed after it is reached up to the desired depth. So, that means the casting was done under the water which was not so effective for the first case the top well, but in case of bottom box well or floating cache and the construction cast is done in the land because as this is the sealed or the bottom is closed condition and can be used when land is not very that means this can be used when the load is not very heavy and bearing strata is up to a shallow depth. So, that means up to shallow depth this can be done and the advantage of this type of well is that that foundation band has to be prepared before and so that the advantage this advantage is done this this is the construction is done in the land. So, it is effective and the disadvantage is that before the it is placed into the ground the land has to be prepared. So, and the bearing capacity of the base has to be properly calculated. So, that otherwise it it is very difficult to construct this type of well into the soil. So, that means when we calculate the this prepared the bed and then the calculate the bearing capacity all this factor then the scouring of the foundation action has to be incorporated during the calculation. So, next type of well that is first one is the open cache and then the box well and the second one is the pneumatic well. So, this pneumatic well is another type of well foundation. So, that is again this is the water surface and this is ground surface. So, this is constructed in a dry condition. So, in this well the this is excavation is done under the dry condition. So, once the depth required depth is achieved the working chamber is filled with the concrete and the advantage of this type of well that the better control during the sinking and the suspension can be done. The bottom of the chamber can be sealed effectively with concrete under dry condition. So, that means here the first case the concrete bottom of the concrete was sealed under the below the water. So, which is not so effective but here the concrete thing is done the it is bottom of the concrete is sealed under the dry condition which is so effective and the disadvantage is the cost of this type of well is very high and the limit of the depth the penetration below the well is around the 30 to 35 meter. So, that means if we compare the three types of well the first one is the top well where the concrete is done below the water in the wet condition which is not so effective and the second one is concrete is done in the land, but the second one which is applicable if the bearing strata is at the shallow depth and during so and the bearing capacity calculation has to be properly done and the third one is it is also done up to the required depth, but the advantage is that the concreting is done under dry condition which is very effective and the disadvantage and all the advantages explain for the different types of this well in the first case a cost is not high, but concrete is being done in wet condition in the last case it is so high cost is high. So, these are the limitation and the advantages of different types of well and depending upon the cost of the project and the type of the land or the base condition and we have to use the different types of well foundation. Now, next part is that the components of the well foundation so what are the different types of components of the well foundation. So, first for the different types of components first we if we draw that is the first is the pyre or that above that pyre we will we have to place this garter that is the bridge garter that is placed above a bearing. So, this one is the garter this one is the bearing so first this is a bridge garter then this is a bearing then which is placed in a pyre this is top portion then this is the pyre pyre then this various components of this well that will start this is our different components and this is vertical reinforcement of the pyre this portion is this is the concrete then this one is the bottom plug. So, again this is the top plug where again the concrete in is done filled with top plug again this is the bottom plug and here this is sand filling. So, now these are the various components of the pyre so this is the well. So, this is pyre then this one is called as the top plug then this one is bottom plug then this is cutting edge and this is sand filling this one is well cap then this is the body of the well main body of the well that is well staining. Now, these are the various components of the well and now if I draw the section of the same well then we can draw like this these are the horizontal this is vertical reinforcement this is horizontal reinforcement. So, these are the various components so now the purpose of this various type of components. So, when this top filling the this provides contacts between the well cap and the sand filling and this helps to transfer the load which is coming from the structure to the sand filling. So, from here pile cap so it will transfer the load from pile cap to the sand filling that is the purpose of this top plug. Now, the well cap which is made of RCC slab so that is cast with the staining and the well staining that is the main body of this well and the bottom plug after the well is sink up to the desired level then the base is plugged with concrete and this concrete is done for this different types of well it is done in different condition. So, now the cutting edge the purpose of this cutting edge is to cast cuts the soil during the sinking. So, now and this are the various components of this well and the purpose of this components are explained. Now, secondly that during the construction of the excavation of the hole the dredge hole is formed. Now, the definition of this dredge hole is that this is the hole formed during the excavation of the soil and which is filled with sand later on. So, that means during the excavation this hole is formed and this hole is called the dredge hole which is filled with sand later on. So, that means the definition of this one is the hole which is formed due to the excavation of soil during the construction. So, later on it is filled with sand. So, these are the various components. So, this is the x section and these are the horizontal reinforcement and this is the vertical reinforcement which is shown here. So, next part is that what are the various type of shape of the well. So, now the different types of the well that have been explained in the components of the well, now the shape of the well. Now, first that one is called the circular shape of the well or circular well. So, this is type of well that is circular well. So, next one well can be in this form. Well can be in this form. So, this is double d well. Now, well can be in this form also. So, this is dumbbell form of well. So, now, well can be in this form also where this is the circular dredge hole. Now, it can be in this form also. So, the circular dredge hole and this is octagonal shape. So, this is also circular dredge hole and this is octagonal or double octagonal shape. So, these are the various shape of the well. So, depending upon the requirement we have to go for different types of well. Now, the when you construct well we have to keep in mind that the steaming thickness should be sufficient. So, that it can be easily sink into the well and then the dredge hole should be large enough to permit the dredging. So, when another condition is the when you construct the dredge hole that should be large enough and the base of the structure should be sufficiently stable and the size is sufficient to transfer the load. So, this condition you have to taken care when you construct the well. So, next one that will go for that that how we have to calculate the depth of the well. So, now, this if I summarize the other parts that then when the different types of well foundation and these types are in the open well in the box type of well and then the third one is the pneumatic well. So, when we construct this type of well foundation. So, we have to very careful then this the base that we have to construct that should be sufficiently rigid and then that should sufficiently transfer the load from the super structure to the foundation soil. And then depending upon the different types of well then we have to construct it for various different form and various purpose and when these are the various components that will also be designed during the construction of the well. The next we have to be determine the what would be the required depth of a well foundation and how we calculate the depth of the well foundation because the well foundation when you construct in a for a river well then you have to very careful for the scouring effect because that will play a very important role. Then what would be the grip length below the foundation below the scour level then what would be the minimum thickness of the of the or the minimum depth of the foundation that we have to be very carefully designed. So, now the next part that is the depth of the foundation. So, when you construct the depth of the foundation as I mentioned the scouring depth will play a very important role. So, that then this scour depth how we calculate this scour depth because this scour depth means that during this flow of the water the some soil will be taken out by the flow then we have to consider this scouring during our design. So, this scour depth we can calculate that d this scour depth is equal to 0.473 root 3 q y f now where the the and this is d this scour depth is below h f l high flood level. Now, here q is equal to design discharge that is meter cube per second and f is called as less is shield factor that is 1.76 root to the power m where m is equal to mean size of particles in the water millimeter. Now, this when so how we will calculate the design discharge. So, design discharge will calculate. So, that is given parameter. So, that we have to first determine our from the previous history of the site or that is we have to give as a input to calculate the scour depth. So, that maximum discharge or maximum design discharge that we have to consider and then this less is shield function factor will calculate and then how we calculate the m. So, that means the particle size of that area. So, that means soil. So, we have to collect the soil sample for the required depth and then from this soil sample we have to go for particle distribution analysis. So, that grain size distribution analysis that depending upon which type of soil it is. So, I have to go for the sieve analysis or I have to go for the high depth analysis. So, we have the grain size distribution curve. So, once we have the grain size distribution curve then from that grain size distribution curve we can determine what would be the m value. But once we get that grain size distribution curve then we have the grain size distribution so that means here if I draw the grain size distribution curve. So, this is the the particle size which is millimeter. So, that is in the log scale and this is the percent finer. So, we have this type of curve we will get. So, that is the grain size distribution curve and from this grain size distribution curve, we have to calculate the mean size of particles in what is the mean size of this particle and we can take the weighted average of this particle size. So, there will be basically a particle size and from there we calculate what is the average of the particle size of this that area and from that particle size will that will be use as m value and then from using that m value, we can calculate what would be the seal factor F. So, this design discharge as input F we can calculate based on the particle distribution curve or that we have to done by the particle distribution analysis and from that test we can determine the m value and then from that m value we will determine the F and from there we will get the scour depth. What is the scour depth required? Now, once we get the scour depth, then another length that is required is the grip length and now grip length is generally is given by one third of D max. D max means maximum scour depth. Now, according to the IS code that this D max should not be less than 2 meter for pierce and abutment with arches or I mean this grip length that should not be less than 2 meter for pierce and abutment with arches on that should not be less than 1.2 meter for an abutment with other structure. Now, this D max is the maximum scour depth that what will be a maximum scour depth that for IS code also recommends some values that mean that the grip length that we have to provide additional that is one third of the D max. Now, for the D max IS code that IS 3 in 9, 5, 5, 1967 that is recommends some maximum scour depth of the scour value and that depends on the different types of the section of the river in the in state section that this maximum D max is given the 1.27 of D. So, D is given that is the maximum depth of scour depth that we have calculate and this is D max. Similarly, for a moderate bend this value is given by 1.5 D. So, for severe bend this is 1.75 D for right angle bent that is given 2 D. So, depending upon the C P G state section then this will be given as so that the source that is taken is Ranjan and Rao 2000 book. So, now in the state portion if the section is state then we have to provide D max value is 1.27 D and therefore, the moderate bend we have to provide D max is 1.5 D and for severe bend so that is 1.75 D and right angle bends to be 2 D. So, depending upon the section of the river how much D you have to consider so that we can calculate. So, from this one we can calculate the D max and then we have to calculate D you have to calculate for the scour depth and the seal factor does mention. So, for depending once we can one process is we can determine the F value from the laboratory test. So, what would be the F value that we can determine from the laboratory test as I explained then again size distribution analysis you can determine the F value. We can determine the M value and from that M value we can determine the F value. Another option that for different tables and is available tables are available for different types of soil what would be the F value. So, that we can also use are better is we can test the soil from that area from the site and from that testing data we can determine the what would be the M value and based on that we can determine the F value. So, F value we can determine and from there we can determine D value. Now, from this difference type of section we can determine the D max value and then that mean the D max is generally varies 1.27 times to 1.75 or 2 of the D and then from there we can determine the grip length the grip length will be one third of the D max. So, now the what is the minimum depth of the foundation. So, that means it is recommend again I score recommend that the minimum depth of foundation is 1.33 times of the depth of the foundation. So, once we have the D max then what would be the minimum depth of the foundation. So, grip length that we have to add with the foundation with the depth of the foundation. So, that means the minimum depth of the foundation will be as one third is a grip length. So, that will be 1.33 times of the D max. So, below the high flood level. So, once we get the D max or depth of the foundation. So, say the minimum depth of the foundation is the D. So, that is the or the depth of the foundation is the D. So, this is D is the depth of the foundation of the well then at depth what would be the load carrying allowable load carrying capacity of the soil. So, again for this I s 3955 1976 they propose that this will be the depth of the foundation. So, that is at 5.4 n square B plus 1600 plus n square into D. So, by which we can determine what is the allowable load carrying capacity of the soil at the depth of the foundation D. So, now where this q a is the allowable load carrying capacity. So, which is given in kg per meters kg per meter square. This is kg per meter square and then the B is given that is the smaller diameter of the well meter of well section in meter and D is the depth of the foundation below scour level. So, that is in meter and here n is corrected SPT value. So, if I know that this B section and this n is the corrected SPT value then we can determine what would be the allowable load carrying capacity of the soil at the depth D below the scour level. So, now and then we can use that whether the load which is coming on the soil is greater than q a or not. If it and then we apply again we have to apply the factor allowable safety and then we have to check whether the load which is coming on the soil which is greater than of this load or not. Then if it is greater than we have to again redesign these things for the for that particular soil and at that depth. So, and this way we can determine what would be the depth of the foundation. We can determine the required depth of the well foundation and at depth what would be the bearing capacity of the soil and then we have to check during the design this bearing capacity of the soil is good enough to resist the load which is coming from the structure. And then now so again we have mentioned that we have to design these components very accurately because we have some different components of the well foundation. And then when we are constructing the well foundation there should be a lateral load which is coming from the in terms of water pressure or that means these things we have to consider during the design because this q a that I mentioned that is the bearing capacity. But when you design the total well foundation then you have to design some other components of load because that is the water pressure will come then the seismic load that may act during the life period of this well. So, that means the dead load then the those load live load that will come during the construction period during the lifetime of this well. So, that means we have to consider all these things during the design of the well. So, that means that this only bearing capacity calculation that is not enough to design of different components of the well. So, that is the bearing capacity that will give whether fine this load which is coming on the soil which is capable this soil can take that load or not at that depth. So, and depending upon the site conditions we have to then increase the load if it is not sufficient increase the depth of the well if the it is not sufficient to carry that load at the required depth. So, these things now the forces of different forces that is acting that are acting on the well foundation. So, that is different forces if are. So, these forces includes that the wind force that acts on the well foundation the wind force then the seismic force then the force due to the water current current then the force due to the buoyancy then force due to the temperature variation in the next to the force due to the earth pressure. So, these are the forces generally acting on a well foundation and definitely the traffic force load that is also acting on the well foundation in additional to that if it is in the curve then the centrifugal force will also act into the well foundation. So, when we design this well foundation we have to consider all these forces which are acting on the well foundation during design and this lateral earth pressure this earth pressure is the basically the lateral earth pressure which is acting on the well foundation due to the soil surrounded by the well. Now, when these all combination of force we have to apply and then based on then we can calculate what would be the net horizontal force that is acting on the well what is the moment that is acting on the base of the well then what is the vertical or downward force that is acting on the well including the self weight of the well. So, these forces we have forces to be considered during the design of a well foundation. Now in this class I have also discussed about the dimension part then the depth part and now these forces we have to consider during the design and now the design methodology that are available. So, that is basically there are few methods that is available one is Tazakhis method. So, another is the first method for the design when you are talking about the design of a well foundation then we are talking about the lateral stability of the well. So, what how we can check whether the well is stable under lateral force or the combination of force or a force a moment whether the well is stable or not. So, this lateral stability of this well we have to check whether this well is stable or not now the different analysis are available that is for the Tazakhis analysis then the pender's analysis then Banerjee and Ganga Padda's analysis IRC also a common one design or lateral stability check methodology and that is IRC 45. So, by using these methods we can check whether the well which is laterally stable or not and that among this methodology I will discuss about this IRC method and that will be discussed in the next class. Then how we can check the lateral stability of the well how we can check then because this lateral stability are basically from the moment that is coming. So, that means the resisting moment that should be greater than the moment which is acting on the well or the base of the well and another check that the bearing capacity check that means the load which is acting or the stress which is acting on the soil. So, soil should be able to carry that stress. So, that means the we have to check whether that moment which is applied in the well that should be a counterbalance by the well foundation. So, that means that is one check moment check another one the that soil pressure that is sufficient the soil pressure which is coming on the soil. So, that means soil is sufficient to carry that load and then we have to check another condition the horizontal force which is acting. So, that means that should be a counterbalance or a resisting force we have to that sufficient to counterbalance that horizontal force. That means we have to check whether horizontal force which is for horizontal force checking have to check for the moment which is acting and have to check whether soil pressure is acting on the base of the soil which is sufficient or not. So, once we design or we check all these things then after this checking of this well foundation we can say now this dimension we can provide for this particular condition. So, first we have to consider this load or combination of loads and then based on that we consider what would be the net horizontal pressure or force what is the moment net moment acting on the base of the well and then based on that we have to consider the what is the net vertical force that is acting on the well. So, vertical force horizontal force and then the moment that is acting on the base those we have to calculate and then we have to check whether this thing soil can able to take this vertical state acting on the soil that is able to take on soil is able to take on not. So, that means that means the check that is we have to consider that for this purpose that what are the check that means the first check is with the summation of the vertical force and the next one summation of the horizontal force and the next one summation of the moment. So, we have to check all these three things that means the this this is the total downward or force that is including the base reaction and side friction then W H is the net lateral earth pressure including friction that can be at side and base and net one is the summation of the moment including the lateral earth pressure and the friction side and the base. So, these are the force that the three equilibrium condition that means sigma v vertical force summation of the horizontal force and the summation of the moment that we have to check and according to that we have to check whether the well can resist this horizontal force and the soil can resist this vertical force or the stress which is acting on the soil and the moment which is acting on the well.