Field Testing on active isolation of vibrating foundations in Middle-frequency range

Open or in-filled trenches are usually used for suppressing disturbing ground vibrations induced by various man-made sources such as construction activities, transportation systems and power plants. However, using a trench to suppress low-frequency excitations, may be either impractical or inefficient. This study evaluates different mitigation strategies to suppress middle-frequency ground vibrations (i.e. between 25 and 40 Hz), generated by a rotating mass vibrator mounted on a shallow foundation in the field. The mitigation strategies encompassed placing isolating materials including sand-rubber mixture (SRM) in bags and block-type EPS geofoam, in sidewalls and bottom of a cubic pit excavated underneath the vibrating foundation and then backfilling the pit. Using EPS geofoam resulted in up to 30% and 20% reduction in ground vibration amplitudes of vertical and horizontal components, respectively. However, SRM-filled bags provided better efficiency which increased with rubber content. For instance, up to 40% and 50% reduction were observed, respectively in vertical and horizontal ground vibrations, when a SRM mixture with 25% rubber content was used. The excavation depth in current study was comparably lower than that of an open trench, for the same vibration reduction level, and thus considerably reduced the earthwork volume.