The shearing and dilatation of dry sand and the 'singing’ mechanism

The state of internal stress existing within a uniformly dilated array of solids undergoing uniform shear, and the relation of the stresses to the dilatation and shear rate, were examined experimentally in a previous paper (Bagnold 1954). Since the dilatation could only be controlled under gravity-free conditions wherein the solids were suspended in a liquid of the same density, the generality of the results remained uncertain. As a test of the generality these results are now applied to the very different conditions in which a mass of dry natural sand is bull-dozed over a single shear surface. When the push is applied by a force which is virtually independent of the motion it causes, e. g. via a long spring, the displacement of the sand mass occurs by a succession of intermittent jumps, each at a velocity which is predictable from the earlier work. It also appears possible from the earlier work to explain the cause of the hitherto mysterious sounds emitted by certain natural sands and to predict the frequencies of the sounds.