The accuracy needed could be established based on the criteria for 

 maintenance. The degree of damage determines the method of repair. 

 Piling is wrapped when damage is between 5 and 15% of the cross-sectional 

 area. When damage is between 15 and 50%, the piling is repaired with 

 grout or concrete. When damage exceeds 50%, the piling or the damaged 

 area is replaced with wood or concrete (Ref 3) . For both economic and 

 safety purposes, the accuracy required should be between 10 and 15%. 

 After 15% cross-sectional area loss, the strength of the pile is affected 

 and the cost for repair increases. 



Current methods of inspecting waterfront structures do not meet the 

 accuracy required to prevent unexpected or catastrophic failures, par- 

 ticularly in critical waterfront facilities that directly impact Fleet 

 operational readiness. Current methods of inspection include visual 

 surveys, incremental coring, resistance probing, and hammer sounding. 

 In addition, ultrasonic inspection of wood piles is currently being used 

 by Agi and Associates, a consulting firm located in Vancouver, British 

 Columbia, which has often inspected Navy facilities. 



Visual inspection, the most common method of inspecting underwater 

 structures, is an essential part of any structural survey and can provide 

 information on defects and external condition. However, numerous defects 

 are not visually detectable, particularly in timber waterfront structures. 

 Pilings that appear to be sound may suffer over a 50% loss in cross- 

 sectional area from marine borer infestation. In core sampling one or 

 more small diameter cores are removed for examination to determine the 

 internal condition of the piling. Core samples indicate the pile condi- 

 tion in the exact location of the core. The major disadvantage of incre- 

 mental core inspection is the small probability of intersecting a mollusk 

 tunnel unless the infestation has reached advanced stages. Resistance 

 probing and hammer sounding give only gross indication of internal condi- 

 tion and are typically only successful in identifying extensive deteri- 

 oration. 



The ultrasonic equipment used by Agi and Associates was developed 

 by B.C. Research of Vancouver, British Columbia. B.C. Research studies 

 revealed that the remaining cross-sectional area could be correlated 

 with the ultrasonic measurement only to within 25%. This is due to the 

 inherent variations in wood strength and the effects that differing 

 eccentricities of the damage in the cross-sectional area have on the 

 buckling and bending moments for the pile (Ref 4) . The detailed capabil- 

 ities of the ultrasonic inspection technique used by Agi and Associates 

 are discussed in this report in the section on Commercial Ultrasonic 

 Capabilities Demonstration. 



POTENTIAL TECHNIQUES 



Passive Sonic Testing 



During research to determine growth rates of Bankia and Teredo, 

 Professor E.C. Haderlie of the Naval Postgraduate School, Monterey, 

 Calif., found he could detect the presence and location of borers in 

 timber laboratory test panels. The borers were detected by listening 



