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Common construction activities such as caisson drilling, excavations and soil compaction may produce ground vibrations that are potentially damaging to nearby structures. Vibration-induced damages may range from cosmetic hairline cracking in wallboard and stucco to structural damages that may threaten the integrity of the structure. To minimize potential for property owner claims related to damage associated with vibrations, we recommend that ground vibrations be evaluated and monitored. Vibrations that may be disturbing to humans may have characteristics that do not threaten any portion of a structure. Likewise, vibrations with potentially damaging characteristics may be largely imperceptible by humans. Quantitative measurements of ground vibrations at a construction site may be used to determine if activities exceed threshold levels which could cause property damage to nearby structures. Thus, claims attributed to vibration damage can be evaluated with quantified vibration monitoring.
Implementing an appropriate strategy for ground vibration evaluation and monitoring on a site-specific basis may vary with site conditions and construction activities. Techniques and recommended procedures have been defined by various state, federal and international agencies. Criteria have been established by AASHTO, ACI, USBM and other agencies to quantify vibration levels considered capable of causing damage to structures. Modern equipment is capable of recording the waveform as well as the relative levels of the vibrations. The waveform records allow the ability for the operator to discern whether the vibrations are of a transient or steady-state nature. It has been found that for given levels of particle velocity, steady-state vibrations are capable of causing far more damage than transient or impulse signals. During the course of daily monitoring, a continuous record of construction-generated signals is recorded and events near critical levels are recorded in greater detail. A Field Activity Log is maintained to describe construction activities at given times throughout each day. Notes are taken to describe any activity considered potentially able to produce relatively larger impulses or vibration signals. Based on these records, it can be determined if ground vibrations generated during construction activities reached levels which would potentially damage adjacent structures. It is the responsibility of the owner, or of his representative, to take the necessary steps to see that the contractor and subcontractors modify activities in the field to control vibration levels. |
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