Eurocode 7: difficulties for designers in its practical application
28 June 2016
This research is being conducted on behalf of Dr Trevor Orr of Trinity College Dublin who is also a member of the CEN SC7 committee responsible for the revision of Eurocode 7. The aim of the project is to investigate how Eurocode 7 is currently being used in practice in Ireland while also examining how the design code has affected geotechnical engineering design in this country.
Eurocode 7 is the European standard for geotechnical design and became the Irish Standard for geotechnical design in 2010. The geotechnical design standard sets out a methodology on how to address the uncertainty and risk involved in geotechnical engineering design. Eurocode 7 is a single code comprising two parts covering all aspects of design for different types of geotechnical structures, including geotechnical investigations and the determination and selection of geotechnical parameters.
The code includes sections on areas such as the basis of geotechnical design, spread foundations, pile foundations, anchorages, retaining structures and embankments, hydraulic failure and overall stability as well as on geotechnical data, supervision of construction, monitoring and maintenance, fill construction, dewatering, ground improvement and reinforcement.
The role of Part 2 of Eurocode 7 is devoted to laboratory and field testing. It is primarily to cover the planning of the tests, their evaluation and, finally, the derivation of values of geotechnical parameters. These are the basis for the characteristic values to be determined by Part 1 as input to design models.
Eurocode 7 is based on the Limit State Design concept and characteristic values and the world’s first geotechnical design code to share a common philosophy with the design methodology for structures (Ibrahim et al, 2013). The head Eurocode, EN 1990 – Basis of design, provides the design principles and requirements for structures. This is adopted in Eurocode 7 for geotechnical design, which is the limit state concept used in conjunction with the partial factor method (Orr, 2012).
The use of Limit State Design philosophy in geotechnical design means an increased agreement and understanding between geotechnical and structural engineers, as well as consistent levels of safety and serviceability. This should result in more economical designs, while offering a clearer distinction between Ultimate Limit State (ULS) and Serviceability Limit State (SLS) than in working state design because they are defined clearly within the code.
Background to research
Eurocode 7 adopts a different design philosophy than previously used in geotechnical design practice in Ireland. The code’s use of separate limit states and partial factors, rather than global factors of safety or working stresses, are a change from traditional geotechnical design practice in Ireland. This requires a change in conceptual approach: instead of finding a collapse load and factoring it, it is necessary to define actions (loads) and resistances for the problem to ensure the actions are less than the resistances.
To ensure reliability of the design, partial factors are applied to the actions and resistances/material properties. It presents a unified set of principles for all geotechnical design and connects the divide between geotechnical design and superstructure design that previously existed (Driscoll et al, 2008).
Unlike the Eurocodes for structural materials, Eurocode 7 leaves the method used for calculations of allowable values to the judgment of the designer. This is due to the fact that different calculation models are used in the different CEN countries and rather than include particular models in the code text, it was decided instead to select the most commonly used and best agreed models (Orr, 2012a).
Eurocode 7 provides numerous lists of items to be considered and to be taken into account or checked in a geotechnical design. Through these checklists, Eurocode 7 identifies what has to be achieved, but generally does not specify how. Hence, the code involves a risk-analysis approach to design that requires engineers to identify all the different hazards involved.
Due to this open interpretation of Eurocode 7, there is currently no general indication of the design methods used by practising engineers, as Eurocode 7 focuses more on the management of the design process than on the details of the design calculations.
It has been shown in previous research conducted after the implementation of Eurocode 7 that some challenges existed with its practical application. Any investigation in Ireland on its practical use after the code’s implementation in 2010 was restricted, due to the decline in construction activity during the economic downturn at the time.
Consequently, the purpose of this research is to investigate how the code is currently being used in Ireland and to examine if there is any misinterpretation or lack of experience which may result in errors in design. It is intended to look at items such as:
- What methods are being used to check and verify limit states?
- What calculation models are being used?
- Are long-term evaluations of performance being conducted?
We intend to examine if there are any difficulties in applying the code in practise for items such as:
- How is soil variability taken into account when selecting soil parameters?
- Are site investigations being carried out for temporary structures?
- What calculation models are being used for pile designs?
It is also intended to examine the current challenges in using numerical methods in accordance with Eurocode 7 for a number of different practical geotechnical problems, looking at items such as:
- What design approaches are being selected and why?
- How are water pressures being treated in design situations?
- What are the factors of safety that designs are typically resulting in for the common types of geotechnical structures such as spread and pile foundations?
It is proposed to review how the code is currently being used for typical design situations and complete a comparison with how it was intended to be used, while discussing the effects this has on the resulting geotechnical designs.
In order to prepare for the revision of Eurocode 7 in 2020, there is a need to investigate its current use in engineering practice today. There is no broad picture of how Eurocode 7 is currently being used in Ireland or what difficulties designers are facing six years after its implementation. This project will address the gap in information and provide a research-based insight into the use of Eurocode 7 in engineering practice. The research will see if engineers are designing in complete compliance with Eurocode 7 or just in accordance with its principles.
Conclusions and survey link
In conclusion, the intention of this research project is to illustrate some of the difficulties that engineering consultancies are experiencing in the practical application of Eurocode 7. It is intended to examine if geotechnical designs have become more economical than the previous traditional method of design using a global factor of safety. This research will facilitate feedback from practising engineers within Ireland which may in turn contribute to the development of the next revision of Eurocode 7 in 2020 to generate a more user-friendly design standard.
If you could please click on the link below and complete the survey to help facilitate the research it would be greatly appreciated (it should take no longer than 20 minutes). Everyone who completes the survey will be entered into a draw for a €200 One4All gift voucher. Please feel free to distribute this survey to fellow engineering colleagues for completion. A sincere thank you for your consideration and hopeful participation.
Author: David Fitzpatrick chartered engineer, Wexford
Driscoll, R., Scott, P. and Powell, J., (2008). EC7-implications for UK practice. Construction Industry Research and Information Association, London, UK, Ciria Report C, 641.
Ibrahim, A.M., Malik, I. and Omar, O.A., (2013). Pile design using Eurocode 7: A case study. Journal of Civil Engineering and Construction Technology, 4(3), pp.70-80.
Orr, T.L.L., (2012). Implementing Eurocode 7 to achieve reliable geotechnical designs. Modern Geotechnical Design Codes of Practice: Implementation, Application and Development, 1, p.72.
Orr, T.L.L., (2012a). How Eurocode 7 has affected geotechnical design: a review. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 165, 337-350.