OUR HARBOUR WORKS.

Auckland Star, Volume XXXIX, Issue 183, 1 August 1908, Page 4

OUR HARBOUR WORKS.

We are far from desiring to jaise any sort of "scare" about the condition of the wharves and other works that the Harbour Board now has under construction; but it seems to us that the report just furnished to the Board by the acting engineer supplies some very substantial food for reflection. Mr Powell was instructed by the Board to report upon certain alleged defects in. our harbour works, to which the Board's attention had been called by Mr Bradney, and his comments upon them are such as to deserve careful consideration at the hands of those responsible for the permanency and efficiency of our wharves and jetties. We may say at once that there is nothing sensational in Mr Powell's report; that is to say, it does not justify any serious apprehension as to the stability of the wharves, for the present. But the condition of things that it discloses certainly raises once more in an acute form the all-important questions on which we have frequently dwelt in these columns —whether ferroconcrete has been used on a large enough scale and for a sufficient period of time to prove itself an unqualified success for the special purposes for which it is being used here, and whether, if it is still in the experimental stage, we are justified in committing ourselves entirely and solely to its use without leaving ourselves any chance of revising our judgment, and withdrawing in time if the experiment should prove a failure?

Throe of tlie points with which Mr Powell's roport deals are not directly concerned with the value of ferro-eoncrete as material for piles or wharves. The. shattering of certain piles in the new Railway Wharf appears to have been due to the structural weakness'of the wharffront, which is now to be strengthened. Instead of the Spring buffer pites -origin" ally specified in the contract, to s.ive tho face of the wharf, solid fixed fenders have been substituted, apparently by agreement between the Board's Engineer and the Ferro-eoncrete Company; and we presume that there are sound technical reasons for the change. But by far the most important feature of the report is the section headed "damage to concrete by rusting, of steel." On May 19, Mr Powell found '"rather serious evidence" of such corrosion in piles and beams of the Railway Wharf, and on July 20, on a second visit, he found that

"many spots had developed into cracks, the rusting evidently having gone on rapidly in the meantime.*' Similar marks were found in the under-struc-tuxe of the new Queen - street Wharf and the Ferry Jetty ; and the report adds that "places that were broken out, cleaned and plastered tip two months ago have again developed signs of rusting, in some cases to the extent of cracking the cement." Mr Po-well, however, considers that there i 3 not the slightest ground for alarm as to the security of these structures, for the reason that "in no instance in any of the -wharves examined is there any sign of rusting that can be attributed to the steel in any of the piles where the original concrete is existing." The rust marks and consequent cracks occur only in broken sections of the piles; "and it is found invariably that whero rusting occurs the steel approaches too near the surface." We presume that this means that in Mr Powell's opinion there is no danger of corrosion where tho air and water have not been able to get at the steel rods through crack's. At tße same time the report specifically states that a thickness of 11 inches of concrete is needed -to secure-thc steel absolutely against risk. "This is the figure given in our specifications," says Mr Powell," and if rigidly adhered to would avert all trouble." As Mr Powell has found 133 rust marks on piles and 117 on diagonal braces directly due to the steel in the Railway Wharf alone, we ■fear that the only possible inference is that careful attention has not always been paid to what he describes as a "sufficient margin for safety."

We have no doubt that Mr. Powell's opinion as to'the stability of these wharves is sound and satisfactory so far as present conditions go. But the suggestion that adequate precautions have not been taken to protect the steel rods from all risk of corrosion in case of accidental cracks or fractures is certainly very disquieting and it appears to us fully to justify the proposal put forward by Mr. Bradney for a complete investigation of the facts, or at least a discussion by the Board of the whole position.