Shear Wave Velocity Measurements Before and After Dynamic Compaction of Cohesionless Soil Deposits
Phil C. Sirles*, Geophysicist, U.S. Bureau of Reclamation, Denver, Colorado
Crosshole shear wave velocity measurements were used to evaluate the effectiveness of dynamic compaction of foundation soils at the Jackson Lake damsite, Wyoming. This investigation method quantitatively assesses the change with depth in the low strain elastic properties of the soils after dynamic compaction. Shear wave velocity measurements from three sites show that shear wave velocities increased within the upper 35 feet
(10.7 meters) by approximately 28 percent. Generally, the fine grained silty sand layers showed slightly greater velocity increases than layers with higher percentage of gravels. The investigation demonstrates the ability of crosshole seismic testing to identify changes with depth in the elastic properties of cohesionless soil deposits due to dynamic compaction.