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Correspondence

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.