Partial factors: where to apply them?

The application of partial factor design in geotechnics has been under debate for several decades. Although the approach has some obvious, and generally accepted, benefits, it has proved very difficult to reach agreement on where in the calculation process partial factors should be applied. In this paper, it is argued that four issues should determine the point in calculations at which factors are applied: • the factors should directly cover the principal uncertainties involved in the calculation, whilst also adequately covering secondary uncertainties • the factors should lead to designs in which both geometry and strength are adequate and compatible • the factors should not be applied to quantities which may become negligible as a result of a balance between loads (actions)