Discussion of “Minimum and Maximum Densities of Granular Materials” by G. R. Mehdiratta and G. E. Triandafilidis

Abstract

The discussers raise points relating to the need for a new standard that would obviate the excessive amounts of poorly controlled vibration common in U.S. test methods. It is noted that maximum dry density can often be obtained with completely dry material. It is also noted that the depth of material in the container being vibrated has a significant effect on the density; for greater depths of material a greater amplitude of vibration was required to achieve the maximum density. It is pointed out that during vibration of well-graded materilas there is a tendency for the finer particles to work their way downward to the lower parts of the sample. Observations made during the compaction of laboratory samples of a crushed limestone aggregate are used to illustrate these points. It is concluded that the specification of simple harmonic motion of the soil container for compaction of granular materials by vibration would be much simpler to perform if instead of using several frequencies and amplitudes of vibration, a single frequency with a steadily reducing amplitude were specified. The method can be adapted for well-graded material, but allowance must be made for the downward movement of fine particles during compaction. The author responds to the points raised by the discussers regarding the migration of coarser particles to the top, the observations made on the limestone aggregate, the progressive reduction of amplitude and ellimination of the need for performing tests at different amplitudes, and the topic of confinement.