The strength of bulk materials increases with the addition of moisture and reaches a peak at some point beyond which additional moisture reduces the bulk strength. This point at which maximum strength is achieved can be determined in a Jenike style shear testing machine to enable design for worst case conditions.
The basic idea of the Penetration Method has its origin in this phenomenon. A test sample in a cylindrical vessel is subjected to vertical vibration of acceleration X in 50/60 Hz exerted thereon. To judge liquefaction, a penetration bit of P gf/cm2 as the weight is placed on the surface of the sample. When the penetration depth of the bit exceeds a criterion D mm for T minutes, it is judged that the liquefaction occurred. Otherwise, the moisture content of the sample is less than the FMP.
Low Consolidation Testing:
Flow properties tests are performed using a nike style shear testing machine. These tests the bulk strength and internal friction angles as functions of major consolidation stress for the bulk material, which allows calculation of storage facility design parameters. The consolidation stresses acting in a correctly designed hopper under flow conditions are relatively low. MAasurements of material properties at low consolidation pressures, including determination of compressibility (bulk density as a function of major consolidation pressures) and wall friction, allows calculation of design parameters to define the basic geometry of mass flow hoppers. Variable hopper geometry design charts will provide the necessary information to relate hopper half angles with critical arching dimensions and anticipated flow rates for both a conical and plane flow hopper design.
High Consolidation Testing:
When designing gravity reclaim stockpiles or large funnel flow storage bins, higher consolidation pressures need to be considered. Measurement of the bulk strength at high consolidation stresses allows calculation of draw-down angles and critical rathole dimensions for use in stockpile, expanded flow and reclaim bin design.