Determination of characteristic values for marine clay
Recently, limit state design (LSD) in geotechnical engineering has been developed through LRFD in North America and Eurocode 7 in Europe. LRFD is an approach that estimates resistance by design model and that multiplies resistance factor by calculated resistance to reflect the uncertainty of materials and design models. Whereas, Eurocode 7 employs the partial resistance factor applied directly to each variable in resistance equation that individual soil properties such as cohesion and angle of internal friction are applied. Current methods of estimating characteristic value were discussed with the marine clay of Korea within the framework of characteristic value which has globally argued during the processing of development of Eurocode 7 for geotechnical design. Estimation of characteristic value, an issue of this dispute, affects not only determination of design value applied directly to design of geotechnical structures, but also economic feasibility and stability following results of design. In this paper, the characteristic values for main marine clay were calculated and compared with using some methods proposed. As a result, it was appeared that most of the computed values were close to mean value and less conservative in the order of Student/Ovesen, Schneider and EN 1990. In case of EN 1990 approach, however, it was inappropriate to assess geotechnical design value being calculated less than zero with statistical variability. Also, it was found that current methods have trend of estimating more conservative characteristic values when larger in ground variability.
Development and implementation of Eurocode 7
The development of Eurocode 7, the new European standard for geotechnical design, is traced from the decision of the European Commission in 1975 to establish a set of harmonized technical rules for structural design, known as the Eurocodes, to remove the barriers to trade within the EEC. The stages involved in the development of Eurocode 7 from the first committee meeting in 1981 to the publication in 2004 of EN 1997-1, the European Standard version of Eurocode 7, are outlined. The challenges that had to be overcome in preparing a geotechnical design code that harmonized geotechnical design with structural design within the Eurocode framework are explained. The process of implementing Eurocode 7 as a national standard in each European country through the preparation of National Annexes is outlined. Details are given of Nationally Determined Parameters chosen for the Irish National Annex. The Irish National Annex with the text of EN 1997-1 was published in 2007 as I.S. EN 1997-1 and is the first Irish standard for geotechnical design. The significance of this is that Eurocode 7 can now be used for geotechnical design in Ireland and will be called up in public contracts from 31 March 2010, which is when the Eurocode Era is due to start. The Development and Implementation of Eurocode 7 Orr T.L.L 2 1. Background: 1975-1980 Eurocode 7, the new European code for geotechnical design, is one of the set of 58 Eurocodes for structural, including geotechnical, design throughout Europe. The concept of the Eurocodes arose as a consequence of the European Commission deciding in 1975 on an action programme to remove the barriers to trade in construction within the member states of the European Community. Within this action programme the Commission took the initiative to establish a set of harmonised technical rules, known as the Eurocodes. It was intended that the Eurocodes would, at a first stage, serve as an alternative to the national standards and, ultimately, would replace them. It was also decided to base the Eurocodes on the limit state design method with characteristic values and partial factors. A Eurocode Steering Committee to oversee the work on the Eurocodes was established by the section of the Directorate General for the Internal Market, DG3.1. In 1979 a geotechnical engineer on the Eurocode Steering Committee informed the International Society for Soil mechanics and Foundation Engineering (ISSMFE) of the proposal to prepare a Eurocode for geotechnical design. Professor Kevin Nash, Secretary General of the ISSMFE, wrote to the EC stating that the ISSMFE was keenly interested to become involved in the work on EC 7 and to draft a proposal for Eurocode 7. This paper outlines the stages in the development of Eurocode 7, the challenges that had to be overcome, the process for its implementation in the CEN Member States and the main features of the Irish National Annex for Eurocode 7. 2. Model Code Stage: 1981 1987 Following the Professor Nash’s letter to the EC, the ISSMFE sought to identify a suitable person to chair a sub-committee to prepare the draft Eurocode 7. Following consultations with geotechnical engineers in Europe, Professor Fukuoka, president of the ISSMFE, asked Professor Nash in 1980 to invite Professor Niels Krebs Ovesen of the Danish Engineering Academy to chair the subcommittee and produce a model code for Eurocode 7. In 1980, invitations were sent to each of the eight geotechnical societies within the nine EEC countries at that time to nominate a representative to this committee. These nine countries were Belgium, Denmark, France, Germany, Ireland, Italy, the Netherlands and the UK; Luxembourg does not have a separate geotechnical society. The first meeting of this committee took place in Brussels in March 1981, by which time Greece had joined the EEC and so was represented at the meeting. Trevor Orr was appointed as the representative of the Geotechnical Society of Ireland on this committee and attended its second meeting in Stockholm in June 1981 during the 11 International Conference on Soil Mechanics and Geotechnical Engineering. The year 1981 was a time of change in the ISSMFE: Professor Nash died unexpectedly and Professor John Burland acted for a short period as Secretary General until Dr. R.H.G. Parry was appointed; Professor Fukuoka was succeeded by Professor Victor de Mello as President. The recently established Eurocode 7 subcommittee caused a problem for the new ISSMFE Steering Committee under Professor de Mello as it was a unique committee and was functioning without the status of a normal ISSMFE technical committee. Also, the members of the ISSMFE Steering Committee felt that the ISSMFE should not be engaged in drafting codes of practice. Hence, on 20 November 1981, Professor de Mello wrote to all the member societies stating that the status of the sub-committee on Eurocode 7 was under reconsideration. Subsequently, on 12 May 1982, John Burland, a member of the Steering Committee, wrote to Niels Krebs Ovesen, as requested by Professor de Mello, suggesting that the committee should be designated an ad-hoc committee consisting of representatives from the nine member societies of the ISSMFE. It was agreed with Krebs Ovesen that when the final draft had been produced it would go to the nine ISSMFE member societies who would express their views on the draft. The draft would then be sent to the European Commission with the views of the member societies. Also the following statement relating to the ad-hoc committee appears in the minutes of the ISSMFE Steering Committee meeting in May 1983: Any publication of this committee should not imply responsibility of the ISSMFE. The withdrawal of ISSMFE sponsorship from the committee, while disappointing, did not in fact affect its work nor did it result in any members leaving the committee. The members were happy to continue working on the ad-hoc committee for their national societies under the leadership of Niels Krebs Ovesen. When Portugal and Spain joined the EEC in 1985, representatives from these countries also joined the ad-hoc committee. Meetings were held in the countries of the committee members so that, as well as drafting the model code, they learnt about the geotechnical practices in the different countries. The eighth meeting was held in Dublin at the Institution of Engineers of Ireland in January 1983. Figure 1 is a photograph of those who attended that meeting. After 22 meetings held in the 6 years between 1981 and 1987, the ad-hoc committee completed its work and submitted the draft model code for Eurocode 7 shown in Figure 2 to the European Commission in December 1987. It is stated in this document that it had been prepared by representatives of the geotechnical societies within the European Communities so that, as agreed by Niels Krebs Ovesen, it is clear it was not an ISSMFE approved document. 3. First Draft Stage: 1988 1989 Once the model code for Eurocode 7 had been submitted, the European Commission then formed a smaller 7-member Drafting Panel to convert the model code into the standard Eurocode 7. Niels Krebs Ovesen was appointed Chairman of this Drafting Panel. Trevor Orr Transactions of Engineers Ireland, 2007 3 Figure 1: Eurocode 7 Ad-hoc Committee members at Meeting in the IEI, Dublin, January 1983
EUROCODE 7: A COMMENTARY
Eurocode 7 part 1 covering geotechnical design was published as a European pre-standard by CEN in October 1994 and by BSI in 1995 as DD ENV 1997-1:1995. Two years later, in 1997, Eurocode 7 Part 1 was subjected to voting and accepted in July 1997 for further development to become an EN (European standard, or Euronorm). Since this process may take several years, the 1995 publication forms the basis of this commentary. The commentary is in five parts: (a) fundamentals; (B) important features of EC 7 part 1; (c) clause by clause commentary; (d) the way ahead; (e) worked examples.