Geotechnical design according to Eurocode 7 and French national standards

Eurocode 7, published in France in 2005 for part 1 and in 2007 for part 2, deals respectively with geotechnical calculations and soil investigation for geotechnical studies. Together with the other so-called "structural" Eurocodes, it enables the justification of foundations for buildings, bridges, towers, masts and chimneys, retaining screens and their anchorages, retaining walls and various earth structures (embankments, cuttings, reinforced earth walls, nailed walls, etc.). Earthworks and certain types of structures, such as dams and tunnels, are not covered by Eurocode 7.

To be applicable in France, Eurocode 7 – Part 1 is accompanied by a national appendix and six national application standards:

• NF P 94-261 standard for surface foundations;

• NF P 94-262 standard for deep foundations;

• Standard NF P 94-270 for reinforced soil structures;

• Standard NF P 94-281 for retaining walls;

• Standard NF P 94-282 for retaining walls;

• standard NF P 94-290 for earth structures.

In the short term, these six standards will replace older normative texts such as fascicule 62 Titre V or DTU 13.12 and 13.2. They are already applicable, however, and transcribe the principles of justification of geotechnical structures according to Eurocode 7 in line with French practice.

With regard to the design of geotechnical structures, the main change brought about by the application of Eurocode 7 and its national application standards is the systematic use of justification formalism for serviceability limit states and ultimate limit states. Various combinations of actions are considered, and partial coefficients must be applied to the actions and resistances to justify the projected structure with sufficient safety. It is essential to specify that these changes do not introduce any modifications in the overall safety levels previously considered, except when the revision of calculation models has led to proposed optimizations.

This chapter describes the general content of Eurocode 7, with particular emphasis on Part 1. The dimensioning of foundations and supports is described by presenting in succession the standards NF P 94-261, NF P 94-262, NF P 94-282 and NF P 94-281. In each case, the most important aspects of dimensioning are highlighted, so as to give the reader a global and practical vision of this body of texts.