Basic results from full-scale tests at Fort Drum

This paper summarizes the principal results from two sets of full-scale tests of high-energy blast sound-absorbing surfaces. Test I involved two 3.66-m-square pits over which charges of military C-4 explosive were detonated. Pit 1 had a top layer of coarse gravel, a middle layer of pea gravel, and a bottom layer of coarse sand; Pit 2 had a homogeneous layer of pea gravel. Data from pressure gages at a distance of 2.6-m indicated that Pit 2 absorbed the sound of the blasts relative to the blast sounds measured over a grassy Reference Site, while Pit 1 was not absorptive at this distance. At a distance of 15 m, the opposite was true. The same trend that was evident at the 15-m distance was also evident at the 250-m distance, to a lesser extent. Test II involved plowing the ground in a region extending from a blast site. The plowed ground attenuated the blast sound at all frequencies of interest at distances up to 100 m. At distances greater than 100 m, the sound exposure level of the blast waves was attenuated for frequencies greater than 100 Hz but increased for frequencies less than 100 Hz. Some of the low-frequency data from both Tests seemed to implicate ground elasticity effects. Overall these tests indicate that the reduction of blast sound by local sound-absorbing surfaces is feasible and should receive further development.