Use of geotechnical numerical methods with Eurocode 7

The first extensive coverage of numerical methods in a geotechnical design code has required extensive study within the geotechnical numerical analysis community, focused on the pros and cons of the different factoring approaches to verifying ultimate limit states (ULS) of geotechnical structures. The resistance factoring approach may be used to verify adequate safety against a particular failure form occurring in relatively simple cases, but for more routine designs the material factoring approach (MFA) is considered more suited to numerical methods. The action effect factoring approach (EFA) applies a relatively constant safety margin to structural forces in most cases, but there are some situations where lower than expected ground strength has a significant effect on structural forces and EFA would not provide adequate reliability. Therefore, a dual factoring approach (MFA and EFA) is recommended where the most onerous structural forces obtained from each are used in the verification of structural ULS. A design example using numerical methods as well as conventional calculation methods is used to illustrate some of the issues where it was found that the selection of calculation method had a far greater influence on many of the outputs of design values than the factoring approach.