48 



ENGINEERING SECTION 



By R. M. Neily and W. H. KiRKHRmE 



with special collaboration from 



F. D. Mattos, H. E. Squire and C. L. Hill 



CHAPTER V 



THE ENGINEER'S RESPONSIBILITY IN 

 MARINE STRUCTURAL PROBLEMS 



It is likely that no type of structure is subjected to such severe and adverse con- 

 ditions as that serving in sea water. The superstructure involves all the problems of 

 those built on land, and the substructure, in addition to being constructed on a com- 

 plex and uncertain foundation, must be capable of resisting the action of tidal currents, 

 waves and storms, impact of ships, abrasion of floating objects, severe weathering 

 action, chemical action of sea water and, in the case of timber substructures, the rav- 

 ages of marine borers. These structures constitute a most necessary and vital element 

 of industry and commerce; they involve the expenditure of great sums of money; 

 they are expensive to maintain; and, when once established, their deterioration is 

 extremely serious, not only because of the direct cost involved but because of the 

 interruption of operation when repairs and replacements are necessary. The obscured 

 and uncertain condition of the substructure presents many obstacles to design, con- 

 struction and maintenance; it sometimes results in sudden failure of the structure, 

 entailing a loss of life and property which could have been avoided had the condition 

 been known. 



The average organization financing a new project demands that type of construc- 

 tion which gives the desired facility at the lowest first cost. In the case of marine 

 structures a lowest first cost usually iuAolves untreated timber piling. The facts that 

 other structures in the vicinity have been built with such substructure material and 

 with apparent success, that no borer attack may have been observed, or that the attack 

 may seem to have been negligible, are by no means sufficient warrant for the conclusion 

 often drawn from them that the borers can be disregarded and that unprotected timber 

 is adequate. It has been amply demonstrated that absence of borers in the past is no 

 assurance of their continued absence. The>- are sufficiently distributed along all sea 

 coasts to appear anywhere and some of them can exist in salinities as low as 5 parts in 

 1,000; sporadic infestations often occur in regions previoush- unmolested; conditions 

 of salinity sometimes change, as for example in river estuaries, increase of salinity 

 bringing with it borers; and it is known that substructures of untreated timber can 

 be destroyed in a few months, the attack being often unnoticed until actual collapse 

 occurs. Teredo navalis settling in the breeding season of July and August has in fact 

 caused the destruction of unprotected piling by the end of October. 



Under these conditions it is ob\ious that a critical responsibility rests with the 

 engineer. Where borer infestation is possible and timber is in\olved, an understanding 

 is required not only of substructure practices but of essential facts respecting the meth- 

 ods of attack, habits, breeding, and life history of the borers themseh-es. If a new 

 project is contemplated, the limited life of untreated timber in that location must be 

 demonstrated and proper protections or substitutes recommended; if the structure of 

 unprotected timber exists, means must be instituted to note carefully the advent of 



