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To the EDITOR of The Structural Engineer. SIR,-In your March issue was published an interesting letter from Mr. Ewart S. Andrews dealing with a problem in connection with retaining wall design, which although frequently arising, in practice is not adequately dealt with in text books.
Mr. MACLEAN GIBSON emphasised the importance of mass in concrete roads. The statements made in this paper with regard to mass concrete roads, he said, were somewhat on the lines of the statements made in a paper which he himself had read before the Yorkshire Branch of the Institution in 1929 (and which was published in the April and May, 1929, issues of The Structural Engineer). In that paper he had referred to some laboratory experiments which had indicated the degrees of compression when certain stresses were imposed on concrete of varying grades and of varying depths. The successful mass concrete roads referred to in that paper were 9 ins. thick, and he did not think my road would be successful unless it had considerable mass; if it were to withstand the shocks imposed by heavy traffic it must have weight. After all, one did not install a machine on a light reinforced slab; one would place it on a mass concrete bed, and bed it down. With regard to joints, he said that on some roads which had cross joints he had stood with one leg on one side of a joint and the other leg on the other side of the joint, and had felt himself sway as a lorry had passed by. Such roads were not very successful. One of the most successful lengths of road he knew of, however, was a road at Hull constructed on the Walker-Weston system; this was constructed five or six years ago, and not a halfpenny had been spent on it since. Its length was not much more than a quarter of a mile, but he travelled over it frequently, and could attain a speed of 50 miles per hour in a car without feeling any effects of the joints. That was a tribute to interlocking joints and short strips. The strips were not longitudinal, but slightly diagonal, and at intervals of about 13 or 14 ft. The road being wide, one did not notice any effects due to the joints when passing over them. There was a very great difference between this portion of the road and the tar Macadam portion, which latter portion had been repaired about six times. Even running on the road was of very great importance, but a great many roads were in his opinion, wrongly designed, inasmuch as the designers had incorporated the old-fashioned practice of constructing a fall to the gully. There were gullies along roads, at intervals of 50 or perhaps 100 ft., and often there were humps between the gullies and a fall to each gully. When motoring along such roads, within 4 or 5 ft. of the kerb, one could feel the waves due to these humps and falls, and he considered that the principle was wrong. His view was that the gutter should be a definite channel next the kerb, and it need not be more than 14-in. deep. No one used the part of the road which was within 9 ins. of tho kerb, except when pulling up, and if a channel 14-in. deep were provided the moisture would have no difficulty in getting away. With regard to Mr. Walker's statement that the efficiency was only 25 per cent. at a corner of a slab, in a road where there was a centra
STRUCTURAL engineering is a term or title often incorrectly interpreted. There was a tendency at one time to use it in particular reference to static structures in steel and reinforced concrete, because, with the growth of these forms of construction, specialisation of production and of professional services in connection therewith, became distinctive, particularly in relation to building. F.E. Drury