Screening of Surface Wave in Soils

Field model tests were performed to determine the effectiveness of trenches in shielding against vibrations transmitted through the ground. In tests designated as active isolation, annular trenches surrounding a vibrating footing were used to reduce the amplitude of vibrations transmitted away from the footing. In tests designated as passive isolation, straight trenches were used as barriers at a distance from a vibrating footing to shield a designated zone. Two indicators of screening effectiveness were studied: (1) The degree of reduction in vibration amplitude, and (2) the shape and extent of the screened zone. In all tests the shallowest trench which provided a prescribed degree of shielding was determined. Trenches were compared on the basis of dimensionless geometrical parameters formed by relating trench dimensions to the wave length of the Rayleigh wave. The relative effectiveness of open trenches and sheet-wall barriers of the same size was also studied.