Fundamental issues in developing a code of practice for geotechnical design – Eurocode 7
Dr Brian Simpson
As Eurocode 7 becomes more widely used in Europe and elsewhere, questions raised by designers have highlighted issues that require further debate and clarification. Most of these have existed in geotechnical engineering for many years, in one form or another, but the advent of a new code, providing a common language, has brought them into sharper focus. Some of these issues will be considered: the selection of characteristic and design values of soil parameters, design in situations dominated by water pressures, the relevance of the EQU limit state and the use of numerical analysis for ULS design.
The selection of parameter values for calculations frequently leads to debates among geotechnical designers. Eurocode 7 attempts, in an rather qualitative way, to point towards a target reliability for characteristic values, while providing a framework in which the precious expertise of individual engineers can be fully exploited. Problems of water pressures and the EQU limit state have a lot in common: how to make provisions for safety in situations where forces largely balance one another and material strength plays a small, but often vital, part. Numerical models are now widely used to study serviceability, but their use in checking ultimate limit states has been questioned; how are partial safety factors to be applied, at what point in staged calculations, and can they be used with advanced non-linear models of soil behaviour? Each of these issues will be discussed and some practical solutions suggested.
Eurocode provides a generalised and very flexible approach that is as applicable to Australasian practice as it is in Europe or the UK. It provides an alternative to local codes and can be employed in situations where local codes are not available or not applicable. The design issues that Brian discusses are also entirely relevant to local practice.
Dr Brian Simpson is an Arup Fellow, a principal of Arup Geotechnics and an Honorary Professor at the University of Nottingham, UK. He has worked on a wide range of geotechnical and ground- structure interaction problems, maintaining particular interests in numerical modelling, retaining structures and tunnels. He presented the BGA Rankine Lecture in 1992 and a State-of-the-Art report on Geotechnical Analysis and Design at the 2009 international conference of ISSMGE. Since the early 1980’s, he has been involved in the development of Eurocode 7 (Geotechnical Design), having been a member of its drafting panels and vice-chairman of the CEN (Comité Européen de Normalisation) committee on Eurocode 7 (SC7). He has authored two commentaries on Eurocode 7 and several papers on various related issues. He is the current chair of ISSMGE Technical Committee TC205 on Safety and serviceability in geotechnical engineering and of the BSI committee on geotechnical codes, B/526. He is often the UK delegate to SC7 and is a member of several of the “Evolution Groups” set up to propose further developments of Eurocode 7.
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