The Nerlerk berm case history: some considerations for the design of hydraulic sand fills

• Published in: Canadian Geotechnical Journal
• Main Author: Konrad, Jean-Marie
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1991
• Subjects: Civil and Structural Engineering; Geotechnical Engineering and Engineering Geology; Beaufort Sea
• Online Access: http://dx.doi.org/10.1139/t91-074; http://www.nrcresearchpress.com/doi/pdf/10.1139/t91-074

Back-analyses of recent large-scale slides during the hydraulic placement of an articial sand island at the Nerlerk site (Beaufort Sea) using different methods have resulted in contradictory conclusions with respect to the state of the fill. All the interpretation methods assume a unique relationship between steady-state strength and void ratio. This assumption is, however, not verified, since steady-state strength depends also on effective confining stress. This paper presents the results of a back-analysis at the Nerlerk site using a modified concept proposed by the author which isbased on nonunique values of steady-state strength for a given sand. It is established that the density conditions at Nerlerk, on average at a relative density of about 40%, and the initial stress conditions are conducive to strain softening, with a steady-state strength corresponding to the minimum strength defined by the LF line. For Nerlerk sand,the minimum undrained strength is about 18% of the steady-state strength determined with conventional methods using high confining stresses. The Nerlerk berm failures were thus "liquefaction" slides induced most likely by progressive straining. Key words: sand, undrained, strength, steady state, hydraulic fill.