Finite element analysis of the Nerlerk underwater berm failures

• Published in: Géotechnique
• Main Authors: Hicks, M. A., Boughrarou, R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Thomas Telford Ltd. 1998
• Subjects: Earth and Planetary Sciences (miscellaneous); Geotechnical Engineering and Engineering Geology; Canada; Mer de Beaufort; Beaufort Sea
• Online Access: http://dx.doi.org/10.1680/geot.1998.48.2.169; https://www.icevirtuallibrary.com/doi/pdf/10.1680/geot.1998.48.2.169

Finite element analyses have been carried out to investigate the possible causes of failure, during construction, of the Nerlerk underwater berm– a hydraulically placed sand slope, designed to form part of a bottom-founded offshore oil exploration platform at Nerlerk in the Canadian Beaufort Sea. The double-hardening Monot constitutive law has been used for modelling the fill materials, while an elastic–perfectly plastic von Mises idealization has been used for modelling the weak underlying clay layer, on which the structure was founded. The computed results demonstrate that, for conditions of rapid loading, there are three possible failure mechanisms, depending on the shear strength of the clay. All mechanisms result in liquefaction of the Nerlerk fill and are hence consistent with the flat post-failure slopes observed on site. However, the most likely cause of failure seems to be that of limited movements in the clay layer triggering liquefaction in the Nerlerk fill near to the berm crest. This investigation represents a major step forward over previously published back-analyses, in that no prior assumptions regarding failure mechanism have been involved. It is also a significant improvement over conventional slope stability calculations, which, for liquefiable soils, tend to greatly overestimate on-site factors of safety. Des analyses des éléments finis ont étéeffectuées pour examiner les causes possibles de la rupture, en cours de construction, de la berme submergée Nerlerk–un talus en sable remblayé hydrauliquement, qui devait faire partie ďune plate-forme de prospecdon pétroliére sous-marine á Nerlerk, dans la mer de Beaufort, au Canada. La loi constitutive du double durcissement Monot a servi á modéliser les matériaux de remblai, tandis qu’une idéalisation élastique parfaitement plastique de von Mises a servi á mod6liser la couche sous-jacente &coron;argile faible sur laquelle reposait &coron;ouvrage. Les résultats calculés montrent que, dans des conditions de charge rapide, il existe trois ...