| The objective of this research is to extend the frequency range for surface reflection techniques for concrete piles using a three-dimensional guided wave approach. This study was conducted in four stages. First, a PC-controlled test system based on requirements found from results of numerical evaluation is developed and integrated. This test system is able to perform waveform generation, vibration measurement, multiple channel data acquisition, and various data processing and analyzing techniques such as digital filtering, Fast Fourier Transform (FFT), and Joint Time-Frequency Analysis (JTFA). Second, a series of small-scale prototype piles with diameters from 152mm (6 inch) to 457mm (18 inch) were constructed in the laboratory; these piles were later on embedded in the National Geotechnical Experimental Site at Northwestern University. These piles are either intact or contain a designed defect. Third, conventional impulse response tests were conducted on these piles. The results are evaluated by three-dimensional guided wave theory. Finally, the procedures to induce waves with a narrow band of frequency content into the piles were developed. The responses were evaluated by comparing the experimental and theoretical results. For interpreting the data using a guided wave approach, special techniques were developed for measuring the bulk shear wave velocity and identifying the mode attribute of acquired waveforms. Results of the research indicate the theoretical guided wave approach is applicable for interpreting the results for both the conventional impulse response tests and the newly developed frequency-controlled test. A new approach for detecting the locations and types of defect that cannot be identified by the impulse response approach was also proposed. |
