Identifying and Assessing Timber Piles Damaged by Teredo Navalis 'Shipworm'

The structural integrity of timber piling is susceptible to degradation by wood boring organisms. Crustacean wood borers known to engineers as Limnoria, which consume the outer surface of timber piling are easily detected during traditional, topical inspection methods. Wood boring molluscs however, present challenges which are not addressed by traditional inspection methods. Wood boring molluscs infest and consume timber, almost exclusively in the underwater zone, without any immediate, detectable damage at the outer surface of the piling. Teredo navalis, the most prolific of the Teredinidae family of wood boring molluscs, has seen a major resurgence on the New York City waterfront in the last thirty years. During a year long period beginning in the spring of 2010, an experimental method of detection, the 1456 Penetration Test, was developed at a site on the New York City waterfront. 5096 timber pilings were probed and analyzed by several inspection dive teams under the guidance of engineers. Hundreds of these piles were later cut and repaired, whereupon the original timber was removed for analysis of internal damage by Teredo navalis. Piling of damage levels reported anywhere from 0% to 100% section loss were included in this process. The variety of sections documented provides a significant opportunity to report on the accuracy of the 1456 Penetration Test. 100 of the sections documented at the site are presented and compared against the experimental inspection method. Statistical analysis is used to model the accuracy of the 1456 Penetration Test method. A discussion on the evolution, biology and behavior of Teredo navalis is included to provide engineers with valuable insight to the pattern and damage encountered in the field. Finally, formulae regarding the structural damage measured via the 1456 Penetration Test are derived and presented, providing engineers with a reliable method of analysis which can be performed in real time during any implementation of the field inspection procedure.