Advanced laboratory characterization of a fine marine sand from Dunkirk, France

Dense fine marine sand is encountered at the Dunkirk ZIP Les Huttes test site located in northern France that has been employed extensively for research into pile behaviour. Laboratory testing of the sand is required to fully characterise site conditions and determine parameter inputs for analysing the field pile experiments. This paper summarises some of the comprehensive laboratory testing programmes undertaken to investigate the sand’s mechanical behaviour, including stress-strain relationships, stiffness and strength anisotropy, cyclic behaviour, and interface shear properties. The paper first reviews the site’s geotechnical conditions and their potential variations over time. The stringent laboratory requirements that are necessary for the accurate measurement of shear stiffness, strength, and creep strains are then discussed, before presenting illustrative results regarding the sand’s small strain stiffness and time-dependent behaviour. The importance of reproducing site conditions and stress states are also addressed in relation to integrating the laboratory research with field observations and analyses of both recent and historical piling experiments at the Dunkirk test site.