Condition Assessment of Installed Timber Piles by Dispersive Wave Propagation

Abstract

Timber piles are widely used for supporting bridges, piers, wharves, and other marine structures. As they age, it becomes critical that their in situ condition be assessed so their remaining service life can be evaluated. Current inspection methods involving visual examinations and sounding tests are unable to quantitatively disclose a pile's degree of deterioration, depth of penetration, or remaining load-bearing capacity. Years of exposure to wood-decomposing fungi and weathering may have substantially decreased a pile's effective cross-sectional area, so that the pile can no longer function as originally intended. A study was conducted in which nondestructive dispersive wave propagation tests were applied to both laboratory pile models and field timber piles. The laboratory models consisted of acrylic cylinders having different wall thicknesses to simulate various levels of internal deterioration and timber posts with drilled holes to simulate damage created by marine borers. Seven installed and two uninstalled field timber piles were tested. Laboratory experiments indicated that the dispersive wave propagation test is an excellent means for evaluating the degree of hollowness and borer damage. Field experiments further verified the applicability of the dispersive wave propagation in finding the condition of the installed timber piles. The approaches found to be promising for the condition assessment were (a) phase velocity comparison between the first pass and the return pass and (b) wave speed versus test location. The general trend of the dispersion field in condition assessment is the higher the wave speed, the better the condition.