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The Structural Engineer, Volume 6, Issue 6, 1928
To The Editor of The Structural Engineer. Sir :- The May issue of The Structural Engineer contained a letter written to you by Mr. Godfrey, in which he attributed the failure of the St. Francis Dam in California to neglect to provide for upward pressure.
THE PRESIDENT said Mr. Snelgrove had given them a very interesting paper, as all would agree; more particularly with regard to that remarkable tank they had seen practically on the ground. It reminded him rather of an interesting little bath he had himself had something to do with, and which had failed for variousreasons. It was not a concrete tank, but a brick-walled bath or tank with a concrete bottom. The owners had endeavoured to make it water-tight by simply concreting up the cracks, and the remarkable thing was that these repairs were quite satisfactory for a few months of the year, and then the tank inevitably gave out when they wanted to use it for a swimming festival. The reason was that the bath was sunk entirely below the ground level, and on two sides there was a little stream from which they derived their water higher up. The stream ran at no great distance from the wall, and in the wet weather the earth was thoroughly saturated, and full pressure was produced against the sides; but when the summer came the earth dried out. You could pnt your hand down between the backing and the side of the tank, and, of course, the pressure of the water did not rest.
Mr. President and Gentlemen, a word of apology is first necessary. It was only after the printing of the programme that I realised that the time allotted this evening would be too short for the purpose of developing the theme I had originally in mind and prepared under the title of this paper. The choice then lay between an abridgement and a selection. By your leave the latter is here chosen, and the intention is now to present brief observations upon certain details of tank design and to describe two examples, of recent date, which, it is hoped, may furnish material for discussion. E. Copeland Snelgrove