Discussion

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.

To the Editor of The Structural Engineer. Sir,-I have read with considerable interest the paper by Lt.-Col. J. Mitchell Moncrieff relating to earth pressure theories, published in the Journal dated March 28. I beg to refer to his remarks on page 71 concerning the road bridge over the River Tyne at Newburn. Col. Moncrieff would like to know why the average frictional resistance was less at 474 ft., 62 ft. and 65 ft., than at 22 ft., 20 ft. and 21 ft. I venture to suggest that lateral pressure does not always increase with depth as commonly supposed, except in the case of a perfectly dry granular material, and that to a certain degree the reverse is found when there is cohesion; in other words it is cohesion that increases with the depth, due probably to the greater compactness of the material, brought about by the increased weight, and also to the fact that the portion closer to the surface is subject to atmospheric changes, ground water.

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