Presented by Armin W. Stuedlein, PhD, P.E., F.ASCE

This Presentation describes a series of dynamic, in-situ tests conducted within natural soil deposits to deduce their seismic and post-seismic responses and presents side-by-side comparison to the results of cyclic and post-cyclic laboratory test programs and/or laboratory test-based models to establish the similarities and differences between the two techniques. The deposits investigated included a low plasticity silt deposit at mean depth of 2.5 m, a moderate to high plasticity silt deposit at a depth of approximately 10 m, and a medium dense sand deposit at a depth of about 25 m. Two methods for applying seismic loading in-situ were deployed: vibroseis shaking and controlled blasting. In-shaking responses considered include relationships between direct simple shear- (DSS-) equivalent shear strain and maximum and residual excess pore pressure, and cyclic resistance. Post-shaking responses are compared in terms of settlements and volumetric strains to general and site-specific post-cyclic volumetric strain models for the medium dense sand and medium to high plasticity silt deposits, respectively. The post-shaking monotonic undrained shear strength of the medium to high plasticity silt deposit is compared to a site-specific post-cyclic strength model. Key issues surrounding the differences between laboratory and in-situ testing are identified and highlight relevant factors contributing to observed similarities and differences in the observations, including use of reconstituted specimens, and the effects of multidirectional shaking, partial drainage, and excess pore pressure redistribution – effects which are difficult to simulate in the laboratory.