The sliding phenomenon which is reported to impose a restriction upon the slope of slurry pipelines is investigated experimentallv. Two different types of behavior which could be called "sliding" were observed.At pipe inclianations greater than 22" to the horizontal, fully settled layers of solid particles would slide with shear occurring a t or near the pipe wall. The critical angle of inclination increased as the particle size decreased.When the slurry was not fully settled, a natural convective flow process was observed to move the slurry down a pipe incline. This flow occurred at much lower pipe inclinations. Concentration profiles measured near the bottom of a pipe incline showed little effect of slurry type or concentration, provided the slurry contained a significant amount of slowly settling solids. In this case, pipe slope was the most important variable.he experimental work reported in this communi-T cation was stimulated by the statement"' that in the design of the Savage River Iron Concentrate slurry pipeline, pipe slopes were restricted to values less than 14% (9") to prevent sliding of the slurry on the pipe wall a t shutdown. The practical effect of such a restriction could be to increase construction costs of slurry pipelines in hilly terrain. In view of the importance of capital costs upon the economics of slurry pipelines, it was considered desirable to investigate this phenomenon as fully as possible using laboratory scale equipment. It was hoped that laboratory experiments using short lengths of small (2-in I.D.) pipe could establish the effects of slurry type, slurry concentration and pipe slope and could contribute a qualitative understanding of the process. The extremely important variables of pipe diameter and pipe length were not amenable to systematic investigation and no definitive conclusions about these variables can be drawn from the studies reported here. However, it is fortunate that such inferences as may be drawn from the present work suggest that it may well be relevant to the problem of larger, longer pipelines. Experimental studies of the effect of these two variables are currently being planned. Static friction at the pipe wallWhen one considered the angle of internal friction of a fluid-particle mixture of the concentration of a typical settled bed, the original statement was difficult to understand. Since the angle of repose approaches the angle of internal friction fairly nearly and since angles of repose of the order of 30" are not uncommon, even for submerged solid particles, it was very difficult to accept the sliding phenomenon as one which resulted from shear within the particle On a ktudik expkrimentalement le phknomhne de glissement qui, rapporte-t-on, nkessite des restrictions sur la pente des pipe-lines dans lesquels on transporte des matikres solides m suspension. On a observk deux types diffkrents de "glissements".Lorsque les inclinaisons des canalisations exddaient un angle de 22" par rapport B I'horizontale, les couches bien ktablies des matitres solides ont g...

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