Time-Dependent Cone Penetration Resistance of a Postliquefaction Sand Deposit at Shallow Depth

The liquefaction resistance of postliquefaction sand is time-dependent and still largely unknown. In this paper, the time-dependent liquefaction resistance of a postliquefaction sand deposit is studied using 1-g shake table experimental modeling and piezocone penetration testing (CPTu). A uniform liquefiable sand deposit was air-pluviated and fully saturated in a large laminar shear box ($\mathrm{L}\times \mathrm{W}\times \mathrm{H}\text{:}2.29\times 2.13\times 1.83\mathrm{m}$). The sand deposit was subjected to a shaking event in the laminar shear box. Piezometers were embedded at different depths to capture the seismic response of liquefied sand. The measured excess pore pressures were used to verify the occurrence of liquefaction. A series of CPTu tests were conducted to measure the cone penetration resistance, friction resistance, and pore water pressure throughout the depth of the sand deposit prior to shaking and at different elapsed times following the shaking. To capture the sand aging effect after liquefaction, CPTu tests were done at different locations over a total elapsed time of 135 days. This research found that the cone penetration resistance of the sand deposit decreased significantly immediately after liquefaction compared with that before liquefaction. The cone penetration resistance of the postliquefaction sand deposit increased with time; a relationship between cone penetration resistance and time at different effective stresses is proposed. This research suggests that even a short period of time might have a significant effect on soil properties; aging time between earthquake and field tests cannot be neglected and should be documented for better data interpretation.