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, saturated sand deposits at two sites were disturbed using explosives, an Impact PierTM mandrel, or the UTexas NEES vibroseis (T-Rex). One site is located in Griffin, in, where explosives at T-Rex were used, and the other site is in New Madrid, MO, where the Impact PierTM mandrel was used. Subsequent to the disturbance, a series of in-situ tests were performed, to include cone penetration tests (CPT), at varying time intervals (weeks, months, years) to monitor for aging effects. the reason for using the three 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 and the Impact PierTM mandrel 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. However, a laboratory study is currently ongoing to more fully understand these field observations.