This cheat sheet contains a method for calculating a drained bearing capacity in accordance with BS8004, which is non-contradictory complimentary information to BS EN 1997.
The method is similar to the one set out in Annex D of BS EN 1997-1, but includes some additional factors to account for depth, ground inclination and rigidity of the base.
If the resultant load on a foundation is within the middle third, then the true pressure distribution across the base will peak at one side and vary linearly across the base to a lower value on the opposite edge. However, bearing capacity factors are based on a uniformly loaded area. Therefore, the first step of the calculation is to calculate the equivalent uniformly loaded rectangular area, which gives the effective bearing pressure.
The drained bearing resistance is calculated by determining the bearing capacity factors Nq and Ngamma, and applying factors for:
- Foundation shape
- Inclination of load (due to horizontal forces)
- Depth of embedment into the ground
- Base inclination
- Ground/surface inclination
- Rigidity of foundation
Values for most factors have been pre-calculated.
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