Use of the utexas vibroseis in the neesr sand aging field experiment

The objective of this study is to develop a better understanding of the mechanisms and implications of time-dependent changes in the state and properties of recently disturbed sands (i.e., sand "aging"). Particular emphasis is placed on the use of the UTexas NEES vibroseis in this 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. As part of this study, two separate regions of a saturated sand deposit site in Griffin, IN were disturbed using explosives and the UTexas NEES vibroseis (T-Rex). Subsequent to the disturbances, in-situ tests were performed, to include cone penetration tests (CPT) and shear wave velocity measurements, at varying time intervals (weeks, months, and years) to monitor for aging effects. The reason for using the two methods to disturb the deposits is because each method induces different levels of strains, affects the soil state differently, and/or introduces foreign elements into the soil (e.g., blast gases from explosives). Consequently, further insights into the underlying mechanisms of sand aging can be gained. In the area where explosives were used to disturb the soil, increases in CPT tip resistances were observed as a function of time after disturbance. However, in the area where the vibroseis was used, no increase in CPT tip resistance was observed as a function of time after disturbance. This is thought to be due to the relatively low level of strain induced in the soil during the vibroseis shaking.