Dynamic response of saturated dense sand in laminated centrifuge container

A highly instrumented centrifuge experiment was conducted at the Univ. of California at Davis, to investigate the seismic response of a saturated dense sand stratum. Nevada sand at about 100% relative density was employed in a laminated (flexible shear beam) container to simulate one-dimensional site response. Among the total of 27 imparted earthquake-like shaking events, peak accelerations near ground surface ranged from 0.03 to 1.7g (in prototype scale), covering linear to highly nonlinear scenarios. This comprehensive set of recorded downhole accelerations is utilized herein to identify variation of shear modulus and damping ratio with shear strain amplitude. The estimated modulus reduction and damping ratio display a confinement dependence. At shear strains below about 0.2%, modulus variation is found in reasonable agreement with the formulae of Hardin-Drnevich and the modulus reduction bounds of Seed-Idriss, while damping is generally higher. At shear strains larger than 0.2%, the shear-induced dilation tendency maintained secant shear modulus at about 20% of its initial value, with a 20% damping ratio approximately. In earlier laboratory experimental studies on loose to medium-dense sands, Vucetic and Matasovic also reported similar trends. Based on the findings, a two-phase (solid and fluid) fully coupled nonlinear finite element program is calibrated and used to conduct numerical simulations of representative weak to strong shaking events. The computational results are in good agreement with the recorded counterparts, and satisfactorily reproduce the important dilation effects.