There are really three methods, not two.
Rectangular, triangular and prism.
They can be used separately or together. It comes down to conditions and judgment.
Rectangular pressure works as surcharge, as mentioned in the question, or as a worst-case/ conservative scenario.
Triangular methods are easy to calculate. The assumption is that they are pretty close to reality and that quality control of construction and materials represent a larger divergence than the calculation method.
The prism method uses a soils report or calculation to determine the angle of repose for the soil. This is a method that more closely resembles the loading characteristics of the soil in use.
So, it comes down to:
- what are site conditions
- what information is available
- what are structural concerns or priorities
MKDesign 