[mithun]

What is ultimate bearing capacity of soils ??

Ultimate bearing capacity of soils - The loading intensity which causes soil rupture and lateral displacement resulting in rapid sinking of the loaded area into the ground. The intensity of loading, at the base of foundation, at which soil support fails in shear is called ultimate bearing capacity of soils.

It is the theoretical maximum pressure which can be supported without failure.


When excessive load is transmitted to the soil by structural foundation, the settlement of the foundation takes place which is dangerous for the stability of the structure. The settlement due to load can be because of

(i) the soil below footing gets compressed by certain amount and

(ii) The concentrated stresses developed can be so high as to cause actual rupture (shear failure) and displacement of soil below.


Building Structure mostly fails due to unequal settlement or differential settlement.

[mithun]

[/b] Permissible Settlement or Allowable Bearing Capacity
No structural damage to interior finish or partition walls etc. occurrs in buildings investigated at angular distortion smaller than 1:300. For any given structure there is certain amount of settlement either uniform or differential or both which can be tolerated without creating unsafe conditions. This is termed as permissible settlement.

OR

[b]Safe Bearing Capacity of Soils
The maximum intensity of loading that the soil will safely carry without risk of shear failure is called safe bearing capacity of soil. This is obtained by dividing the ultimate bearing capacity by a certain factor of safety, and it is the value which is used in the design of foundation. The factor of safety normally varies from 2 to 3.

Allowable bearing capacity is the ultimate bearing capacity divided by a factor of safety.

This value varies from 50 mm to 100 mm for different type of structures, foundations (isolated or raft) in different types of soils.

[Manish Jain]

Ultimate Bearing Capacity (UBC):  The intensity of loading, at the base of foundation, at which soil support fails in shear is called ultimate bearing capacity of soils. 
It is the least pressure which would cause shear failure if the supporting soil immediately below and adjacent to a foundation. The ultimate bearing capacity is defined as the maximum gross pressure intensity at the base of the foundation at which the soil does not fail in shear. When the term bearing capacity is used, it may be understood to be the UBC

Safe Bearing Capacity of Soils (SBC):
The maximum intensity of loading that the soil will safely carry without risk of shear failure is called safe bearing capacity of so/I. This is obtained by dividing the ultimate bearing capacity by a certain factor of safety, and it is the value which is used in the design of foundation

Allowable Bearing Pressure (ABC):
It ¡s the maximum allowable net loading intensity which can be applied to the soil taking into account the ultimate bearing capacity, the amount and kind of settlement expected and the ability of the given structure to withstand the settlement. It is, therefore, dependent upon both the sub-soil and the type of building proposed to be erected thereon.