2014-069 - Final Environmental Impact Report No. 2014-01

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HARBOR BLVD. MIXED USE TRANSIT CORRIDOR PLAN FINAL FIR CITY OF SANTA ANA 5. Environmental Analysis NOISE cause annoyance due to noise generated from vibration of a structure or items within a structure. This type of vibration is best measured in velocity and acceleration. The three main wave types of concern in the propagation of groundborne vibrations are surface or Rayleigh waves, compression or P- waves, and shear or S- waves. Surface or Rayleigh waves travel along the ground surface. They carry most of their energy along an expanding cylindrical wave front, similar to the ripples produced by throwing a rock into a lake. The particle motion is more or less perpendicular to the direction of propagation (known as retrograde elliptical). ■ Compression or P -waves are body waves that carry their energy along an expanding spherical wave front. The particle motion in these waves is longitudinal, in a push -pull motion. P -waves are analogous to airborne sound waves. ■ Shear or S -waves are also body waves, carrying their energy along an expanding spherical wave front. Unlike P- waves, however, the particle motion is transverse, or perpendicular to the direction of propagation. The peak particle velocity (PPV) or the root mean square (RMS) velocity is usually used to describe vibration amplitudes. PPV is the maximum instantaneous peak of the vibration signal, and RMS is the square root of the average of the squared amplitude of the signal. PPV is more appropriate for evaluating potential building damage, whereas RMS is typically more suitable for evaluating human response. The units for PPV and RMS velocity are normally inches per second (in /sec). Often, vibration is presented and discussed in dB units in order to compress the range of numbers required to describe the vibration. In this study, all PPV and RMS velocity levels are in m /sec, and all vibration levels are in dB relative to one microinch per second (abbreviated as VdB). The threshold of perception is approximately 65 VdB. Typically, ground borne vibration generated by human activities attenuates rapidly with distance from the source of the vibration. Even the more persistent Rayleigh waves decrease relatively quickly as they move away from the source of the vibration. Therefore, manmade vibration problems are usually confined to short distances (500 feet or less) from the source. Construction operations generally include a wide range of activities that can generate ground borne vibration. In general, blasting and demolition of structures generate the highest vibrations. Vibratory compactors or rollers, pile drivers, and pavement breakers can generate perceptible amounts of vibration at up to 200 feet. Heavy trucks can also generate ground borne vibrations, which vary depending on vehicle type, weight, and pavement conditions. Potholes, pavement joints, discontinuities, differential settlement of pavement, etc., all increase the vibration levels from vehicles passing over a road surface. Construction vibration is normally of greater concern than vibration of normal traffic on streets and freeways with smooth pavement conditions. Trains generate substantial quantities of vibration due to their engines, steel wheels, and heavy loads. Page 5.94 PlaceWorkr