Safety of shallow foundations – Limit State Design according to Eurocode 7 vs. alternative design concepts

The main objective of Eurocode 7 was to harmonise geotechnical design in Europe by consistently implementing limit state design. However, Eurocode 7 only provides a framework in which each member state defines the design approach as well as the partial factors according to national design and safety requirements. The design approaches differ in the way partial factors are applied and lead to remarkably different designs especially in the case of shallow foundations under complex loading. Hence, the actual safety of the foundation cannot be reliably determined. In the present paper the correlations between loads and resistances of shallow foundations within Eurocode 7 design are analysed by use of interaction diagrams. The effects of the design approaches on the overall safety are discussed. An alternative design method based on an unique failure criterion for the ultimate limit state is introduced, the implementation of the partial factor concept is discussed.