Shake Table Testing: A High-Resolution Vertical Accelerometer Array for Tracking Shear Wave Velocity

Abstract

Dynamic ground and ground-structure responses are heavily dependent on the soil shear wave velocity. During seismic excitation, soil stiffness inferred from the shear wave velocity (Vs) might change significantly and affect the overall system response. In this study, an instrumentation and analysis framework was developed to allow for continuous estimation of Vs during dynamic/seismic excitation. The framework is presented along with representative applications during shake table testing of saturated sand strata. For that purpose, results from two different 1-g shake table tests conducted in a laminar soil container are examined and analyzed. In this context, evolution of the soil Vs profile during the shaking event is tracked and documented. The experimental setup, test procedure, and test results are described. Time histories of Vs at different depths within the sand strata are discussed. Overall, the developed techniques can be conveniently included in routine 1-g and centrifuge shake table experimentation efforts, when properly accounting for the differences between sizes of 1 g and centrifuge models.

Centrifuge Shake Table Tests on Rocking Footings on Sand

“…For the relatively tall, slender model footing under consideration, the rotational flexibility of the soil reduces the natural frequency more so than the translational flexibility. Given typical shear wave velocities (Vs) near 100 m/s, for recently placed Ottawa F-65 sand reported by Zayed et al (2021), the natural frequency of the 250 mm high (Hsoil) sand deposit in the laminar container would be approximately 4Hsoil / Vs = 100 Hz. Conveniently then, the sand deposit's natural frequency closely mirrors that of the model footing.…”

“…In this study, Ottawa F-65 sand was chosen owing to its uniformity and thorough characterization in literature (e.g., Bastidas 2016;Zayed et al 2017;Zayed et al 2021). In developing the pluviation technique, passing the sand through a pair of sieves (No.…”

Seismic Response of Rail Embankments

“…The selected rail embankment specimen has a weight of approximately 550 kN (container weight not included). Although the weight surpasses the recommended capacity of the shake table by about 35%, previous tests have also been performed on this range of payloads (e.g., Zheng et al 2019;Zayed et al 2020).…”

“…After construction of the rail embankment specimen, a series of earthquake motions and sinusoidal motions with different frequencies were applied. Although the shake table could be operated in displacement or acceleration control, experience with previous studies involving heavy payloads on the UCSD Powell Laboratory shake table (e.g., Zheng et al 2018Zheng et al , 2019Zayed et al 2020) indicate that the shake table performs better when operated in displacement control. Before each applied earthquake or sinusoidal motion, a white noise motion with small amplitude was applied to the rail embankment specimen for system identification as permanent deformations may lead to a change in the dynamic deformation response.…”