ERTC10 Evaluation of Eurocode 7, is one of the European Technical Committees of the ISSMGE
Together with several other ERTCs, ERTC 10 was involved in organizing a number of workshops on Eurocode 7 and geotechnical design during the ECSMGE in Athens in 2011
A report by Trevor Orr summarizing these workshops was written for Volume 4 of the Conference Proceedings, pages 573-584: “Experiences with the implementation of Eurocode 7”.
Workshop before XVI ECSMGE – September 2015
A joint workshop between ERTC 10: Evaluation of Eurocode 7 and the ISSMGE Technical Committees TC205: Safety and serviceability in geotechnical design and TC304: Engineering Practice of Risk Assessment and Management and ISO19900 – General requirements for offshore structures, was held on Sunday 13 September 2015 just before the ECSMGE in Edinburgh. The following report of the joint workshop is based on notes prepared by Brian Simpson, Chair of TC205.
The programme of the workshop lasted from 10am to 5pm, with a break in the early afternoon so that delegates could also attend the workshop of ERTC7 – Numerical analysis. It consisted of three sessions:
- Ground anchors and foundations
- Design dominated by water pressure
- Characteristic values (with ISO 19900)
Despite the difficulty of having the sessions in advance of the main conference, and parallel with many other TC workshops and the Council meeting, about 30 delegates attended and took part in vigorous discussion. Before the main meeting began, as an audience had arrived early, Brian Simpson showed a presentation that had been sent in by Prof Martin Ziegler, who unfortunately was unable to attend. Noting that “none of the current design approaches [in EC7] is perfect”, Prof Ziegler proposed a return to the “original” formulation, retaining separate factors on materials, resistances, actions and action effects.
- Ground anchors and foundations (chair: Colin Smith)
A significant debate during the recent development of Eurocode 7 has been the difference in approach taken to design of ground anchors and tension piles, which, in some circumstances, perform very similar functions. In particular, all ground anchors are required to be individually tested, but tension piles are not. Adriaan van Seters recommending that acceptance testing be implemented on micropiles as it is on anchors.
Brian Simpson presented a summary of the work of SC7 Evolution Group 1, on a new Section 8 on Ground anchors. Eurocode 7 takes no account of calculation as a design verification of anchors, relying entirely on the results of testing. The terminology used in the new section was explained by thinking through the “Life story of a ground anchor”, including, testing, preloading and use during its design life. Simpson noted the UK has found that when the new section is used in combination with factored variable loading (surcharges), the results are too conservative.
Trevor Orr spoke about Irish practice for the design of anchors, in particular the allowable creep rates adopted. Tim Lansivaara questioned some of the factors of safety required for anchors, especially whether proof loading to high factors is really necessary. In very soft soil it is not possible to stress anchors in retaining walls to such high factors without causing passive failure.
- Design dominated by water pressure (chair: Trevor Orr)
Brian Simpson presented some recent thinking on the “HYD” limit state (hydraulic heave), showing that water pressures must be assessed cautiously, taking account of the worst credible distribution of permeability, and that factors of safety are of little use in correcting for poor assessments of water pressure.
Bernd Schuppener presented a German perspective which aimed to ensure that however safety formats are changed the resulting design is unaffected and remaining the same as for previous German standards. Hence the DA2* approach is preferred, with partial factors chosen to be equivalent to previous global factors. The need for “robustness” in design was acknowledged, one speaker noting the need to design for the theft of dewatering pumps!
- Characteristic values (chair: Lovisa Moritz)
This workshop was joined by Joek Peuchen on behalf of ISO 19900, General requirements for offshore structures. Hans Schneider presented a review of recent developments in the thinking of EC7’s Evolution Group 11, Characterization. He discussed the characterisation of brittle soils such as quick clays for the purposes of design calculations and presented statistical approaches to derivation of characteristic values of soil strength in cases where a limited number of test results is to be combined with pre-existing knowledge.
Joek Peuchen said that resistance factoring is favoured in ISO 19900, in order to geotechnical uncertainties such as uncertainty of the zone/shape/volume of soil involved in a limit state. The representative value of resistance, which is to be factored, is not clearly defined, as has been attempted for characteristic values are in Eurocode 7. However, he considered that both Eurocode 7 and ISO 19900 provide inadequate or ambiguous guidance to practitioners for determination of characteristic values of soil properties. The ISO was intended to be consistent with ISO 2394 – Reliability of structures – released in 2015, but this is work in progress.