Searching for the Sand-Pile Pressure Dip

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Science  02 Aug 1996:
Vol. 273, Issue 5275, pp. 579-580
DOI: 10.1126/science.273.5275.579b


For the past 15 years, physicists have tried—and failed—to explain a perplexing mystery of granular mechanics: A conical pile of poured sand does not exert its maximum pressure on the ground in the middle, directly under the apex, but in a ring around the center point; there is actually a dip in pressure in the middle. Now a group of British and French researchers has proposed a new model of sand piles, in which the main compressive stresses lie along fixed parallel lines. These stress lines, angled precisely halfway between the slope of the pile surface and the vertical, steer the pile's weight away from the center, giving a central pressure dip. Despite its simplicity, the model does a respectable job of reproducing experimental data.