Train [14] conducted tests on simple free flowing materials
(i.e. glass balls, lead shot and sand) to minimize the
complications due to shape and surface characteristics. Four
methods were used, including measuring the angle of repose of
a pile formed on a fixed bed, free-standing pile formed by a
fixed funnel, the angle for particulate materials to slide by tilting
a rectangular box, and the angle formed by materials in a
revolving cylinder. His results showed that the angle of repose
tested using the first and second methods (static angle of repose)
were lower than the third and fourth (dynamic angle of repose)
methods. Chowdhury et al. [15] determined the angle of repose
of a pile of grams formed by slowly moving the filling spout
upward as the pile was formed. He found that the angle of
repose increased nonlinearly with increase in moisture content
(MC). Another angle of repose found in the literature is the“emptying angle of repose”. The emptying angle of repose as
defined by Stroshine [16] is the angle made by bulk materials
after it empties from a flat bottom bucket with a circular orifice.
The emptying angle of repose is different from the previous
definitions of the angle of repose. The angles of repose using the
various methods described previously provide the relative
behavior of the bulk material under various test conditions and
are applicable to various bulk handling scenarios. One of the
practical applications for the use of the piling angle of repose is
in the determination of the footprint and headroom of a flat
storage structure for bulk solids, as well as the locations of
overhead and floor conveying systems to transport the bulk
solid into and out of flat storage structures. Flat storage
structures are particularly used for storage of non-flowing bulk
solids such as bulk biomass particulates (wood chips, chopped
and ground plant biomass) and distillers dried grains with
solubles (DDGS) because they enable the use of mobile loaders
to sweep these solids into transport containers and unloading
conveying trenches.