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Further guidance still needed for Eurocode 7

The challenges of using Eurocode 7 (EC7) were highlighted by speakers at CIRIA’s Geotechnical Issues in Construction conference held in London yesterday.

Imperial College professor David Potts demonstrated some of the challenges that applying EC7’s partial factors presents to numerical modelling. “They can be used for simple models but using partial factors in more complex models can result in different answers,” he said. “More guidance is needed on how to use EC7 in numerical modelling and modellers need to be sure they understand the impact that partial factors can have on results.”

Bam Ritchies engineering manager Richard Garland said that many designers are still using BS8081, which was first published in 1989, for soil nail and anchor design rather than EC7 because of the lack of guidance. “EC7 is more a set of design rules but BS8081 is more a code of practice,” he said.

“EC7 also introduces leaner design and recommends lower factors of safety with the emphasis on investment in better ground investigation to gain better quality data. The problem with this is that often soil nails and ground anchors are not considered as a solution until after the ground investigation. The approach also doesn’t consider factors that can affect long term strength, such as creep.”

Problems with applying EC7 at the ground investigation stage were also discussed and Black & Veatch principal geotechnical engineer Simon Pryce said that while changes in logging and SPT energy ratios had been adopted there were still issues with the code. “Many contractors are still facing issues with gaining samples called for under EC7 and very few factual reports mention the quality class of samples tested,” he said. “There is also an issue of how to use historical ground investigation data – SPT N values cannot be converted as the energy ratio of the rig is unknown.”

It was suggested that the future ground investigations may need to take the European approach of using more insitu testing rather than relying on sampling for laboratory testing.

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