40 The Day the Earth Shook: Controlling Construction-Induced Vibrations in Sensitive Occupancies 323 Fig. 40.1 Construction equipment used as vibration generators 0.01 0.1 1 10 100 1000 10000 100000 1000000 1 10 100 1000 L1 Particle Velocity, micrometer/s Distance from Source (m) Backhoe Caisson Driller Vibratory Roller Backhoe Fit Caisson Fit Roller Fit Fig. 40.2 L1 particle velocity with distance that was driven back and forth over the newly-refilled, caisson-drilled hole. The three different pieces of equipment were considered to be representative of the types to be used for different phases of future construction. The L1 vertical particle velocity at each accelerometer location is shown in Fig. 40.2. As can be seen in Fig. 40.2, the 120-m data point has significantly higher vibration amplitudes than the locations closer to the vibration source. This was explained by the fact that the 5, 10, 15 and 20-m measurements were all taken on the parking lot asphalt or sidewalk, while the 120-m measurement was taken on grass. As such, the soil at the 120-m location could be considered “free soil”, while all other locations were on compacted soil. The density and wave speed of the “free soil” are less than the compacted soil and thus allows for the amplitudes of vibration to increase in order to conserve the intensity of vibrational power flows. Given that all the equipment in the building would be located on compacted soil below the foundations of buildings, only the 5, 10, 15 and 20-m accelerometer locations were used to calculate propagation curve fits. In addition to measuring vibration within the rooms where sensitive equipment is installed, accelerometers were placed in the adjacent bays to quantify the vibration reduction within the building over distance. The L1 particle velocity found in one
RkJQdWJsaXNoZXIy MTMzNzEzMQ==