David Muir Wood will reprise and update his Bjerrum lecture, presented recently in Oslo. The lecture begins with a description of an investigation performed at the WAC Bennett Dam, British Columbia, following the appearance of sinkholes at the dam crest. Investigations showed that there had apparently been movement of fine material out of the core of the dam. To be able to predict the mechanical consequences of such movement of material, a class of soil model that is able to accommodate changes in both density and grading of the soil is required. An outline of features of the Severn-Trent sand model – which incorporates effects of density variation – is presented and a suggestion is made for ways this model might be extended to include effects of changing particle size distribution.
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