Dynamic Compaction of Granular Soils

Dynamic compaction was used to improve foundation conditions beneath a large warehouse in Indianapolis, Ind. Approximately 15 ft of fine to medium sand above the water table was densified significantly by dropping a 6.5 ton weight from a height of 40 ft. SPT and cone penetration tests were made before and after compaction to determine the level of improvement. Field measurements were also made using a seismograph to establish the level of vibration produced by each tamp at various distances away from the impact. It was concluded that the depth of significant influence using falling weights as a technique of dynamic compaction is about half that previously considered attainable. The level of compaction achieved was found to be related to the product of the energy per drop times the total energy per unit area: which corresponds to an N value of approx 30 to 35.