In a comprehensive study, both the compaction-induced vibrations and extent of ground improvement were investigated at a dynamic compaction site. The site of interest was to be compacted by a 16-t (32 kips) weight. First, an attenuation study was conducted to assist in controlling ground vibration from the weight drops. The attenuation study consisted of 20 pilot drops from different heights ranging from 20 to 50 ft. The vibrations were recorded by 20 three-component geophones deployed linearly from 50 to 400 ft from the drop locations. After establishing the site-specific equation of attenuation, weight drop heights were established for different zones based upon the distance to off-site structures. Off-site structures were monitored at select locations during the production phase of the compaction to ensure vibrations were maintained below the established limit. Additionally, pre- and post-compaction measurements of the shear-wave velocity (V_s) were performed using the multichannel analysis of surface waves (MASW) method. MASW is a non-destructive seismic method that measures the dispersion of surface waves (Rayleigh or Love to estimate subsurface stiffness). MASW results indicated that the V_s of the uppermost 8 ft of subsurface increased by up to 300 ft/s, about 60% of its pre-compaction velocity. The next 6 ft exhibited negligible changes in velocity. This agreed reasonably well with the estimated depth of influence for this operation.
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