As a result of segregation, even the presence of as little as 10% fines (-5 mesh) in an ore can lead to serious flow problems in stockpile reclaim via tunnel systems. If the fines are cohesive and gain strength as a function of consolidation pressure, then ratholes may form above discharge hoppers, severely reducing the live capacity of the stockpile, or arches may form across hopper outlets, leading to flow stoppages.
Jenike & Johanson performed a series of tests on scale models of a variety of large storage piles. The purpose of these tests was to compare and measure the live capacity for a pile comprised of coarse, free-flowing material with the capacity of a pile comprised of the same material mixed with different percentages of fines.
We found that when no more than 5% fines was added to the coarse product, complete draw down occurred and the live capacity could be accurately calculated using a 3D CAD program based on knowing only the measured “drawn down” angle of repose. By knowing the properties of the bulk solid, a gravity stockpile reclaim system was correctly designed providing the most economical and effective method of reclaiming the stockpile.