Cpt-based Ultrasonic Probe for P-wave Reflection Imaging of Embedded Objects

نویسندگان

  • Scott J. Brandenberg
  • Joseph Coe
چکیده

The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the State of California or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Abstract: An ultrasonic p‐wave reflection imaging probe is developed and utilized to non‐ invasively image the geometry of a deep foundation supporting a bridge pier. The source ultrasonic transducer emits compressive waves into saturated soil that subsequently transmit to and reflect back from an embedded object, and the receiver transducer measures the reflections which are used to construct an image. The components of the system, including the custom transducer probe and data acquisition hardware, were integrated with the nees@UCLA cone penetration testing (CPT) truck. The transducers have a central frequency of 100kHz, and have a diameter‐to‐wavelength ratio of more than 3 in soft saturated soils with p‐wave velocities similar to water (i.e., 1500m/s). The large diameter‐to‐wavelength ratio gives the transducers a directivity pattern that controls the rate at which wave amplitude attenuates with distance. The transducers are impedance matched to water, and are therefore reasonably efficient transmitters in saturated soil, but inefficient in unsaturated soil. The probe was utilized to successfully image a pile foundation in very soft saturated clay, but returns were not recorded in stiffer and/or unsaturated soils. Causes of the poor returns include the scattering effects of large soil particles, coupling between the transducers and the soil, and drift of the probe out of alignment with the pile foundation. The probe could be very useful for non‐ destructive quality assurance of structural elements constructed in‐situ in soft saturated soils, 2 and provides higher resolution measurements of the shape of the embedded object compared with other available methods.

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تاریخ انتشار 2010