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Liquefaction Resistance of Chlef River Silty Sand: Effect of Low Plastic Fines and other Parameters

Keywords: silty sand , residual strength , fines content , undrained tests , liquefaction

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Abstract:

Silty sands are the most common type of soil that could be involved in both staticand earthquake-induced liquefaction. Most of the recent earthquakes have revealed theliquefaction of silty sands. Therefore, the selection of the appropriate undrained residualshear strength of liquefied soils to be used in the assessment of the post-liquefactionstability of earth dams and other earth structures is becoming a major challenge. A seriesof undrained monotonic and cyclic triaxial tests were carried out on reconstituted saturatedsamples of sand with variation in the fines content ranging from 0 to 50% for themonotonic tests and from 0 to 40% for the cyclic ones, in order to study the influence offines fraction and other parameters on the undrained residual shear strength andliquefaction potential of loose, medium dense and dense silty sand samples (Dr = 12%,50%, 60% and 90%). The results of the monotonic tests show that the stress-strain responseand shear strength behaviour is controlled by the percentage of fines fraction and thesamples become contractive for the studied relative densities (Dr = 12% and 90%). The undrained residual shear strength decreases as the global void ratio decreases and thefines content increases up to 30% fines content. Beyond that, it decreases with increasingthe global void ratio and the fines content. Moreover, the undrained residual strengthdecreases linearly as the fines content and the inter-granular void ratio increase. Cyclictest results show that the increase of the fines fraction accelerates the liquefactionphenomenon for the studied amplitude and the liquefaction resistance decreases with theincrease of the global void ratio and the loading amplitude. We notice that the reduction inthe liquefaction resistance of Chlef sand-silt mixtures becomes very marked for the smallercyclic stress ratios CSR = 0.15 and 0.25.

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