Fundamental study on guided wave testing of cylindrical bars embedded in soil

Ultrasonic guided wave nondestructive evaluation technologies of long, small-diameter cylindrical steel bars embedded in soil have been experimentally studied using piezoelectric probes attached to the sides of the bars. On the basis of calculated attenuation dispersion curves for cylindrical steel bars surrounded by soil, 60- and 120-kHz longitudinal [L(0,1)] modes were chosen as guided waves for pulse echo measurements of 13-mm-diameter cylindrical steel bars in terms of their low attenuation. It is shown that the L(0,1) mode can be selectively transmitted and received by appropriate arrangement and control of probes attached to the sides of the bars. Pulse echo measurements were conducted for a 13-mm-diameter cylindrical steel bar embedded vertically to the ground with an underground depth of two meters. The signal-to-noise ratio of the first reflection signal from the bottom end surface of the embedded bar was estimated to be more than 30 dB for both 60- and 120-kHz L(0,1) modes. The evaluated attenuations of the guided waves in the underground part are adequately low for inspecting long bars and consistent with the calculated attenuation dispersion curve. The results indicate sufficient potential for guided wave testing of long, small-diameter cylindrical steel bars embedded in soil.