INTRODUCTION 



Accurate assessment of the condition of Naval shore facilities is a 

 vital aspect of Fleet readiness. More than two-thirds of the Navy's 

 waterfront structures were built before 1950 and are rapidly deteri- 

 orating. Thirty-five percent of Navy piers are wooden superstructures 

 on wooden piles (Ref 1). An economical maintenance management program 

 for these structures requires development of reliable and accurate under- 

 water timber inspection techniques. 



In 1979, the Naval Civil Engineering Laboratory (NCEL) , under the 

 sponsorship of the Naval Facilities Engineering Command (NAVFAC) , initi- 

 ated a project to improve the Navy's ability to inspect and assess the 

 soundness of the underwater portion of wooden waterfront facilities. 

 The state-of-the-art of underwater nondestructive testing (NDT) and the 

 application of existing or potential NDT techniques were to be evaluated. 

 This report presents the results of laboratory and field evaluation of 

 several potential techniques, particularly acoustic NDT techniques. 



BACKGROUND 



Natural materials, such as wood, often vary inherently to a large 

 degree, and prediction of their properties is considerably more difficult 

 than with man-made materials. Distinguishing the natural property varia- 

 tions from any internal damage of the wood under water has been a major 

 effort at NCEL, and several approaches have been investigated. The types 

 of timber damage, the measurement accuracy requirements for timber piles, 

 and the initial concepts for inspecting wooden waterfront structures are 

 discussed in this report. 



DAMAGE 



Structural damage of timber waterfront structures generally falls 

 into one of two categories: mechanical or biological (Ref 1). Mechanical 

 damage usually results from accidental overloads or abrasion. Accidental 

 overloads can occur during construction from excessive pile driving forces 

 or after construction from large impact loads, such as docking ships. 

 Abrasion typically occurs in the intertidal zone and depends upon the 

 amount and type of material or debris in the water. 



Biological damage to wooden waterfront structures results from the 

 activities of living organisms such as fungi, insects (e.g., termites, 

 ants) , and marine borers. Fungi, the cause of wood rot, are low forms 

 of plant life that depend on organic materials for food. Rot damage 

 usually occurs above water in the splash zone and near the pile cap. 

 Insect damage also occurs above water in the atmospheric and splash zones. 



