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UBC Theses and Dissertations

The microstructure and critical state locus of gap-graded Bennett south moraine sand Swerid, Amy J.


This thesis presents an experimental study carried out on gap-graded materials obtained from the W.A.C. Bennett Dam south moraine borrow source (BSM sand). The experimental work was carried out within a critical state framework to inform the development of a future critical state type model to quantitatively predict the effect of internal erosion in embankment dams under the mechanism of internal instability. An index void ratio testing program was carried out on gap-graded BSM sand to characterize the sand in loose and dense states, and assess the effect of changing finer fraction content on the void ratio of a gap graded mixture. The results of index testing were compared to those of similar gap-graded mixtures and found BSM sand has similar index properties to other binary mixtures. Index test results were used to characterize the microstructure of the gap-graded mixture in loose and dense states. Monotonic triaxial compression testing was carried out on three gap-gradations of BSM sand to: develop the critical state locus (CSL) for the gradations, assess the effects of changing finer fraction content on the CSL in a gap-graded BSM sand, and compare the results to similar gap-graded mixtures. It was found the CSL shifted upwards with decreasing finer fraction while maintaining the same general shape, similar to the behavior of other gap-graded mixtures. The equivalent intergranular void ratio was applied to the extrapolated critical state points obtained for all three tested gradations. It was found all gradations converged to a unique CSL with an excellent fit to the experimental data. This is similar to the behavior reported for other gap-graded mixtures. The findings of this study indicate the equivalent intergranular void ratio can be a useful tool in future constitutive model development.

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