Acoustically Coupled Ground Motion under Controlled Conditions: Trial Study

摘要

A series of ground-motion experiments was done in the Frost Effects ResearchFacility at CRREL in 1985 and 1986 to determine the suitability of the FERF for studies of ground motion induced by low-frequency acoustic sources. A special method of freezing the contents of a FERF test basin by circulating frigid air was effective in freezing sand to a depth of 53 cm. The reverse means of thawing the sand, exposing it to the ambient temperature air in the FERF, did not allow for expeditious warming of the sand during winter months. Acoustically coupled ground motion was measured for sand conditions of dry, unfrozen; dry, frozen; saturated; and hard frozen. Ground-motion amplitude was 30-40% lower in saturated sand than in dry, unfrozen sand. This depth-dependent reduction is attributed to reduced air permeability in the saturated sand. The amplitude of acoustically coupled ground motion in hard frozen sand (sand frozen when wet) was 80-90% lower than in dry, unfrozen sand. Acoustic-to-seismic coupling, Frozen ground, Ground-motion amplitude.