Comparison of Equivalent Linear Site Response Analysis of Loose Gravelly Soil with Centrifuge Modeling Tests

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The purpose of this study is to compare results of site response analysis with the centrifuge model response of gravelly soils. A series of centrifuge modeling tests were performed at 50-g centrifuge gravitational acceleration to simulate a uniform soil profile subjected to a 1-Hz sinusoidal shaking motion with peak amplitudes ranging from 0.01 to 0.10 g. The soil tested in this study is a gravel-sand mixture of 50% gravel and 50% sand by weight, prepared in a loose condition. Dynamic soil properties of the material were assessed based on several methods, including resonant column, centrifuge bender element, and dynamic response of centrifuge model tests. Equivalent linear site response analysis was performed using DEEPSOIL to analyze the response of the same soil column as the prototype soil modeled in the centrifuge. An overall comparison of results shows that the equivalent linear site response analysis does not provide a good agreement of shear stress and shear strain for the loose gravelly soil observed in the centrifuge tests. At the shaking amplitude of 0.05 and 0.1 g, the shear strain appears to be comparable, but the equivalent linear method underestimated the shear stress. For the shaking amplitude of 0.01 g, the equivalent linear method overestimates surface response acceleration at frequencies higher than 2 Hz due to the variation of shear modulus reduction curve. For the shaking amplitude of 0.05 and 0.10 g, the equivalent linear method underestimates the surface response acceleration because the shear modulus decreases as the number of cycles increases.