A Centrifuge Study on the Effects of Soil Gradation on Liquefaction Potential and Dynamic Response

Well-graded, cohesionless alluvial soils are common in the foundations of embankment dams and pose a potential liquefaction risk. Current practice to characterize liquefaction potential uses standard or oversized penetrometers and case-history based relationships developed for clean sands. This assumes that a well-graded soil will behave in a similar manner to a clean sand when subjected to cyclic loading. A series of centrifuge tests on coarse-grained soil mixtures was conducted at the UC Davis Center for Geotechnical Modeling to study the effects of soil gradation on liquefaction potential and dynamic response. Four uniformly-graded soils with mean grain diameters (D[sub]50) ranging from 0.18 to 2.58 mm were used to construct five soil mixtures: two uniformly-graded, two gap-graded and one well-graded. All base soils were deposited in an alluvial environment and were not crushed during processing; thus, any variations in minerology or particle shape are assumed to be consistent with natural deposition. Centrifuge models of each mixture were prepared loose (relative density (D[sub]R) < 50%) and shaken with 15 sequential uniform sine wave loading events of varying peak base acceleration (PBA). High frequency dynamic measurements were obtained during loading to track the mixtures’ dynamic response. Densification was tracked using both high frequency data and physical measurements. The high hydraulic conductivity of the coarsest, uniformly-graded mixture prevented significant excess pore pressure generation (i.e.
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