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Determination of the effect of the slenderness ratio on the results of the triaxial test depends, theoretically, on the boundary conditions induced by (a) shape of the test specimen, (b) manner of the transmission of the external load, and (c) deformations. From a practical point of view enough length should be available to develop two complete cones of failure and the length of the specimen should equal the diameter times the tangent of (45 +ø/2) °. Most workers in the field of triaxial testing of soils accept a slenderness ratio of from 1.5 to 3.0. With slenderness ratios greater than 3, there is a danger of side buckling. With ratios less than 1.5, the whole sample is restrained by the friction of the end loading plates. A 1:5 ratio of particle size to specimen diameter has been developed for sands and may also be applicable to gravels. In the field of bituminous testing a 1: 2 ratio has been found to give sufficient accuracy and a reproducibility for most design and control purposes. An elastic analysis of the triaxial shear test indicates that the absolute dimensions of the cylinder are of no significance and that the stresses depend only on the slenderness ratio. However, experience in the laboratory indicates that the results on the same material with equipment of various dimensions may be quite diverse.

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Proceedings of the Iowa Academy of Science





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©1966 Iowa Academy of Science, Inc.



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