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This paper describes the major aspects of a computerized field vibration measurement system. By using this system, construction-induced vibrations were monitored along the ground surface and with depth within the soil profile. Vibrations were measured by 3-D surface geophones and 3-D bore-hole geophones, and directly recorded and processed by an automated computer data acquisition system. This data acquisition system includes a notebook computer, a PCMCIA data acquisition card, and “virtual instrument” programs developed in the LabView Window environment. The appearance and operation of these “virtual instrument” programs imitate actual instruments, and replace conventional oscilloscopes, voltmeters, counters, and tape recorders. The same computer and data acquisition board can be used to perform different functions by simply changing computer programs. Therefore, the concept of “virtual instrument” can be used to reduce the equipment cost and improve versatility.
The vibration frequency, wave speed, and peak particle velocity were analyzed by the “virtual instrument” programs developed. This system was used to measure the pile driving vibrations in Selma, NC. Within the soil profile, vibration attenuation with depth in both the horizontal and vertical directions was investigated and compared with Rayleigh wave attenuation function in the vertical direction. In this paper, details of the equipment setup, testing procedures, analytical methods, and testing results are provided.
vibration measurement, data acquisition, virtual instrument, frequency, wave speed, attenuation
Project Engineer, Hayward Baker Inc., Santa Paula, CA
Professor, North Carolina State Univ., Raleigh, NC