Sand Aging Field Study

Aging effects in sand, such as increases in penetration resistance with time after deposition, densification, and/or liquefaction, are known to occur in situ, but the causes of these effects are not fully understood. Nonetheless, these effects have important ramifications in earthquake engineering. First, the lack of understanding of the phenomenon is an impediment to quality assurance/quality control (QA/QC) for ground densification projects aimed at mitigating the damaging effects of liquefaction. This can be understood by considering that most liquefaction evaluation procedures correlate liquefaction susceptibility to in situ indices, such as penetration resistance (SPT and CPT) and small strain shear wave velocity (V_s), all of which are influenced by aging. Consequently, it is unclear as to how long after ground densification QA/QC in situ tests should be performed to ensure that the densification was sufficient to mitigate liquefaction susceptibility. Presented herein is an overview of an ongoing sand aging field study where liquefaction is being induced by explosives, vibrocompaction (using a vibroflot), and a NEES vibroseis in a heavily instrumented sand deposit. The state and properties of the sand are being monitored as a function of time after the disruption of the soil structure.