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DEM, dams and dikes

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Embankment dams and flood embankments are probably the largest, man-made, structures that comprise particulate materials (soil). The talk will focus on internal erosion, a phenomenon where water seeping through the embankment can erode some of the embankment materials and pose a risk to embankment integrity. Two key mechanisms will be considered: (1) the performance of filters which layers of sand and gravel placed to prevent erosion of low permeability, fine-grained material and (2) seepage induced internal instability, a mechanism which involves preferential erosion of the finer grains in the embankment filter and transition materials or in the embankment foundation. Considering firstly filter performance, engineers have long recognized the importance of the size of the narrowest points in the void space, which are called constrictions or pore throats. Hitherto attempts to estimate constriction sizes have relied on a number of unproven hypotheses. DEM enables a direct measurement of the sizes of the constrictions in virtual filter samples. Micro Computed Tomography data can be used to confirm the relevance of DEM -derived data. Network analysis can be used to understand the basic mechanisms involved in filter performance. In a gap-graded material, where there are a mixture of coarse and finer grains, there can be significant inhomogeneity. The amount of the overall stress transmitted by the finer grains can be very small, particularly when the proportion of finer grains in the material is small. Consequently these materials can fail lower hydraulic gradients that are typically considered safe in engineering design. DEM simulations have been used to examine in detail the relationship between this stress inhomogeneity and both the proportion of finer grains and the size of the coarse grains relative to the finer grains. Coupled DEM -CFD simulations have then confirmed that the proportion of stress in the finer grains influences the likelihood that these grains will be transported under the action of seepage flow.

This talk is part of the BPI Seminar Series series.

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