 I am here to discuss with you on topic introduction to bearing capacitive soil. Learning outcomes of today's session. At the end of this session, students will be able to explain bearing capacitive soil and its importance in the design of foundations. Let us see what is bearing capacitive soil. Dear friends, bearing capacitive soil is capacity of soil to support the load applied to the ground. The bearing capacitive soil is the maximum average contact pressure between the foundation and the soil, which should not produce shear failure in the soil, ok. So, it is maximum contact pressure between foundation and the soil. In the photograph, you can see uniform pressure acting on soil. Now, what is importance of bearing capacity of soil? Dear students, all sibling structures, whether they are buildings, dams, bridges, etc. are built on soils. A foundation is required to transmit the load of the structure on a larger area of soil, right. The foundation of the structure should be so designed that the soil below does not fail in shear, nor there is the excessive settlement of the structure, ok. And the conventional method of foundation design is based on the concept of bearing capacity, ok. Now, soil when stressed due to loading tends to deform, we know. Now, the resistance to deformation of the soil, it depends upon which parameters or which factors. It depends upon factors like water content, bulk density, angle of internal friction and the manner in which the load is applied on the soil, ok. Now, this maximum load per unit area, which the soil or rock can carry without yielding or displacement is termed as the bearing capacity of soil, remember. Now, soil properties like shear strength, density, permeability, etc. affect the bearing capacity of soil. Dense sand will have more bearing capacity than loose sand, remember, because unit weight of dense sand is more than the loose sand. Now, what is the selection criteria of foundation based on bearing capacity? That we will see. Remember friends, if the bearing capacity of soil is soil at shallow depth is sufficient to safely take the load of the structure, a shallow foundation is provided, ok. Shallow foundation is provided when bearing capacity of soil is sufficient to take the load, right, at shallow depth. Isolated footing, combined footing or strip footing are the options for shallow foundation. We know. These are the options for shallow foundation. Now, deep foundations are provided when soil immediately below the structures does not have adequate bearing capacity, remember. You will have to go for deep foundation in those cases. When soil is not having sufficient bearing capacity, the soil which is immediately below ground. Pile, piers or well are the options for deep foundations. Matte or rough foundation are useful for soil which is subjected to differential settlement or where there is a wide variation in loading between adjacent columns, ok. So, pile foundation is a type of deep foundation. Also piers or well, these are types of deep foundations. Matte foundation or rough foundation is type of shallow foundation, right, and it is provided when differential settlement of the structure is likely to be there. So, this rough foundation will minimize that particular settlement. Now, let us see what is safe bearing capacity of soil. SBC, it is short form. So, SBC can be defined as the maximum load per unit area which the soil will resist safely without displacement, remember, right. The safe bearing capacity is that particular load, maximum load per unit area which this soil will resist safely without any failure displacement. SBC of soil is obtained by dividing ultimate bearing capacity of soil by factor of safety. So, suitable factor of safety is used and ultimate bearing capacity divided by this factor of safety is equal to safe bearing capacity for which the foundation is designed. Let us see some key terms. What is ultimate bearing capacity? It is the maximum pressure that the soil can support, remember. It is the maximum pressure. Now, what is the ultimate net bearing capacity? QU, it is the maximum pressure that the soil can support above its current overburden pressure, above its current overburden pressure. So, overburden pressure is not considered in this particular ultimate net bearing capacity. What is ultimate gross bearing capacity? QU ultimate. It is the sum of ultimate net bearing capacity plus the overburden pressure. It is the sum of ultimate bearing capacity and the overburden pressure above the footing base. So, it is called ultimate gross bearing capacity. What is allowable bearing capacity or safe bearing capacity? It is the working pressure that would ensure a margin of safety against collapse of the structure from shear failure. The allowable bearing capacity is usually a fraction of the ultimate net bearing capacity, remember. And factor of safety is used. What is factor of safety? It is the ratio of the ultimate net bearing capacity to the allowable net bearing capacity or to the applied maximum net vertical stress. So, factor of safety is used to find allowable bearing capacity. And what are the common values of factor of safety used? Those are between 2 to 5 depending upon site conditions. Now, here are safe bearing capacities of some common soils. For example, hard rock according to IS-1904-1978. The hard rock is having 3240 kilo Newton per meter square as its maximum safe bearing capacity. Soft rock like morum and compact gravel 440 kilo Newton per meter square. Coarse sand 440 kilo Newton per meter square. Also fine sand 440 kilo Newton per meter square. Medium sand 245 kilo Newton per meter square. Soft shell stiff clay 100 kilo Newton per meter square. Soft clay 100 kilo Newton per meter square. Very soft clay 50 kilo Newton per meter square. So, these are the common values of bearing capacities of soil. Now, there are different methods of determining bearing capacity of soils, which are those presumptive analysis, the first method. So, from the experience of the geotechnical engineer. Then second, analytical methods. There are analytical methods like Thirzaghi's bearing capacity equation is used for finding. Then plate bearing test or plate load test. This is in situ test, standard penetration test. This is also in situ test taken at site. Then modern testing methods are there. Centrifuge test is there. So, all these are the methods of determining bearing capacities of soil. Here you can see passive zone, active zone and transition zones of the soil pressure distribution below foundation. Bearing capacity failures. Remember friends, a bearing capacity failure is defined as a foundation failure that occurs when the shear stresses in the soil exceed the shear strength of soil. And modes of soil failure are general shear failure, local shear failure and punching shear failure. What is general shear failure? A general shear failure involves total rupture of the underlying soil. And there is continuous shear failure of the soil from below the footing to the ground surface. When the load is plotted versus settlement of the footing, there is a distinct load at which foundation fails. You can find here distinct point of failure in load settlement curve. The bearing stress that causes a sudden catastrophic failure of the foundation. A general shear failure ruptures and pushes of the soil on both sides of the footing. For actual failures in the field, the soil is often pushed up on only one side of the footing with subsequent tilting of the structure. So, this is general shear failure. Now, what is local shear failure? Local shear failure involves rupture of the soil only immediately below the footing. Remember only immediately below the footing. There is soil bulging on both sides of the footing, but bulging is not as significant as general shear. In general shear failure, bulging of soil is significant. Here it is not significant. And it can be considered as a transitional phase between general shear failure and punching shear failure. So, local shear failure will not give you distinct point of ultimate stress. You will have to find it from the graph. This local shear failure occurs for soils that are in a medium dense or firm state. Punching shear failure. So, here the punching occurs. Remember the whole structure subsides below. This is called punching shear failure. Punching shear failure does not develop the distinct shear surfaces associated with the general shear failure. So, this curve also will not give you distinct point where you can find ultimate load. You will have to find a point where curve deviates appreciably. There you will have to locate ultimate stress or bearing capacity of soil. Let us stop while here friends. Here are two questions for you. Write down their answers neatly. Here are the answers. These are the references for today's session. Thank you.