Seismic Liquefaction of Sand at High Confining Pressure

An examination of dynamic responses of clean sand under high effective confining pressure (σ_v^′) is conducted with two centrifuge tests using laminar container. The centrifuge experiments simulate a 5 m saturated clean sand layer under high effective overburden pressure of 6 atm with the relative density of 40%. To achieve the targeted overburden pressure, a dry layer of lead shot with an appropriate thickness was deposited on the top of the clean sand. Viscous fluid was used for saturation to keep a constant prototype permeability. The centrifuge tests were subjected to 10 cycles sinusoidal seismic motions with a different prototype peak acceleration to study the effects of pre-shaking history. Acceleration, pore pressure build-up and dissipation, and shear wave velocity were recorded during and after shaking. The recorded accelerations were further analyzed using an established system identification (SI) technique to evaluate the cyclic stresses and strains induced in the soil deposit. Furthermore, the effects of pre-shaking history were analyzed in the aspects of excess pore pressure build-up, shear wave velocity changes, and soil deposit densification.