In geotechnical engineering, bearing capacity is the capacity of soil to support the loads applied to the ground. The bearing capacity of soil is the maximum average contact pressure between the foundation and the soil which should not produce shear failure in the soil. *Ultimate bearing capacity (q _{f})* is the theoretical maximum pressure which can be supported without failure;

A costly foundation failure is shown in the figure above.

There are three modes of failure that limit bearing capacity: general shear failure, local shear failure, and punching shear failure.

Other methods proposed for bearing capacity of shallow foundations are: Terzaghi's bearing capacity method which is the earliest method proposed in 1943, and Meyerhof's method (1951, 1963).

Brinch Hansen (1970) provided equations to estimate limit bearing capacity for two separate cases of strength parameters: (1) f> 0, and (2) f= 0 (undrained clay). In addition, for each of these cases there are two separate subcases: (a) Either no horizontal component of load or there is a horizontal component of load and it is in the direction of the width of the footing only; or (b) there is a horizontal component of load in the direction of the length of the footing, or in both directions (width and length of the footing). Equations to estimate limit bearing capacity are provided in the following sections for each of these situations.

In all cases, the limit load that can be carried at the bearing level is given by the following equation

Q_{bL} = q_{bL} x A_{f}

In all equations given below involving B and L, if there is eccentricity at the bearing elevation, use B_{eff} in place of B and L_{eff} in place of L, where B_{eff}= B– 2e_{B}, and L_{eff}= L– 2e_{L}. In the unusual case where L– 2e_{L}< B– 2e_{B}, use B_{eff}= L– 2e_{L }and L_{eff}= B– 2e_{B}

where

q_{0} = effective stress at the bearing level for an effective stress analysis, and = total stress at the bearing level for a total stress analysis

Nq = e^{ptanf} tan^{2}(45+f/2)

Nc = cot f ( Nq – 1)

Ng = (Nq-1) tan (1.4f)

In this case you must check for q_{bL} separately in the directions of the width and length of the footing. Use q_{bL} equal to the smaller of the two values.

where

q_{0}= total stress at the bearing level

where c_{a} = adhesive stress acting on the base of footing, which is usually in the range of (0.5 to 1.0) S_{u}.

For a rough base, use c_{a}=S_{u}.

In this case you must check for q_{bL} separately in the directions of the width and length of the footing. Use q_{bL} equal to the smaller of the two values.

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