1PORTABLE SEISMIC ACQUISTION SYSTEM (PSAS) FOR PAVEMENT MASW

A seismic method (e.g., surface- or body-wave method) has been often used in pavement engineering to evaluate such critical constructional parameters as the E-modulus and Poisson’s ratio. Conventional method usually uses one or two-channel recording device (e.g., dynamic signal analyzer) for data acquisition whose cost is by no means trivial. In addition, recent appli-cations with the multichannel approach have drastically improved the effectiveness of the seis-mic method in general and proven a greater potential of the method than ever. A true multi-channel approach, however, would require a multichannel recording device (e.g., a 48-channel seismograph) and so-many accelerometers deployed simultaneously. The high-cost aspect of seismic method would make this otherwise-effective method excluded from consideration during the early stage of project planning. Instead, we propose a cheap, compact, and convenient seismic system that can be used with either conventional or multichannel approach. This Portable Seismic Acquisition System (PSAS) consists of a laptop computer, one or two accelerometers, and a hammer. A 16-bit PC-card (PCMCI bus) readily available nowadays is equipped into the computer as a data acquisition board. With this system, the multichannel measurement is simu-lated through repetitive generation of seismic waves along a linear survey line at different distances from the receiver fixed at a surface point. Data can be processed directly in the field on the same portable computer, only seconds after data acquisition. In combination with the robust dispersion curve analysis by the multichannel approach, this system creates new possibilities for seismic non-destructive testing (NDT) of pavements with on site evaluation. Data acquisition flow chart, signal conditioning, triggering, and other key features of the system are explained. We also present a case of evaluating pavement concrete thickness, E-modulus, and Poisson’s ratio directly in the field using the proposed system