The analytical models used to design and rehabilitate pavements are becoming more sophisticated. The most appropriate process for verifying the accuracy and usefulness of these new analytical models (as well as for calibrating the parameters involved in these models) is to observe th behavior of pavements in the field. Unfortunately, few devices or techniques are available for determining the displacement of a pavement section under actual loads. In addition, the available methods for monitoring the performance of pavements in terms of displacement are expensive and/or inaccurate. One economical alternative is the use of velocity transducers (geophones). Geophones are quite inexpensive and readily available. In additon, if used properly, geophones can provide quite accurate deflection-time histories.The methodology involved in determining deflection from geophones is complex. Proper mathematical manipulation of the geophone record, using signal analysis techniques and theory of vibration, should be carried out so that the deflection-time history can be accurately determined. Fortunately, the necessary mathematical manipulation can be programmed into a portable microcomputer so that the deflection-time history can be obtained rapidly in the field. This paper presentsan overview of theoretical alternatives available for determining the deflection-time history of pavements using geophones. The limitations and advantages of each alternative are discussed. The practicalproblems that should be addressed in developing a proper algorithm for each alternative are also included. Through an illustrative example and a case study, the versatility of using geophones as a tool for determining the deflection-time history of pavements is demonstrated. This paper appears in transportation research record no. 1227, Rigid and flexible pavement design and analysis: unbound granular materials, tire pressures, backcalculation, and design methods.
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