more challenging. Arching can be analyzed by measuring
the cohesive strength of the material. First, the flow function
of the material (i.e., the cohesive strength vs. consolidating
pressure) is measured through laboratory testing. This test
is also conducted according to ASTM D-6128 using a direct
shear tester (2). As in the wall friction test, consolidating
forces are applied to material in a test cell, and the force
required to shear the material is measured. This information
directly relates to a material’s ability to form a cohesive arch
or a rathole. Once the flow function is determined, minimum
outlet sizes required to prevent arching can be calculated
using the design charts published by Jenike (1). Reference 3
provides the step-by-step Jenike method for hopper outlet
calculation based on a material’s cohesive strength.