The load of any structure is finally transmitted to the soil lying below the foundation of the structure. Hence it is essential to know the strength and behavior of the underlying soil.
Bearing Capacity Of Soil:
The maximum load per unit area which the soil can carry without any settlement or displacement is termed as bearing capacity of the soil. Bearing capacity of soil is determined by the following two methods:
1. Dropping weight method
2. Slowly applying load method.
Ultimate Bearing Capacity Of Soil:
The minimum load on unit area causing failure is called the ultimate bearing capacity of the soil.
Safe Bearing Capacity Of Soil:
The maximum intensity of loading that the soil will safely carry without the risk of shear failure is called safe bearing capacity of the soil. It is obtained by dividing the ultimate bearing capacity by a certain factor of safety which is used in the design of foundation. The value of factor of safety varies from 2 to 3 depending upon the nature of the soil.
Maximum Safe Bearing Capacity Of Different Types Of Soil:
1. Soft, wet clay or muddy clay — 5,000 kg/m2
2. Soft clay — 10,000 kg/m2
3. Fine, loose and dry sand — 10,000 kg/m2
4. Black cotton soil — 15,000 kg/m2
5. Moist clay and sand clay Mixture — 15,000 kg/m2
6. Loose gravel — 25,000 kg/m2
7. Medium clay — 25,000 kg/m2
8. Medium, compact and dry sand — 25,000 kg/m2
9. Compact clay — 45,000 kg/m2
10. Compact sand — 45,000 kg/m2
11. Compact gravel — 45,000 kg/m2
12. Soft rocks — 45,000 kg/m2
13. Laminated rock such as sand stone & Lime stone — 165,000 kg/m2
14. Hard rocks such as granite, diorite, trap– 330,000 kg/m2
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