The behavior of static and vibrated granular beds is explored through measurements of the power required to rotate a vane within the granular media and capacitance measurements to evaluate local density. These measurements of “granular rheology” aim to define a quantitative framework for granular bed states and transitions between these states. The effects of bed height, bed diameter, vibration frequency and glass bead size on the observed states and transitions are explored. Deep granular beds are subjected to vibration in the frequency range of 10 Hz to 300 Hz with acceleration in the range 0 to 4.0g. The bed aspect ratio (effective bed height to bed diameter) is varied up to 4.1 with effective bed height range from 0 cm to 23 cm and bed diameter from 5.6 cm to 7.5cm.

Through measurements of vane power and granular density, three granular bed states, the static granular state, the quasi-static state and vibro-fluidized state, along with the transitions between the states are identified. A granular bed state phase diagram is constructed, mapping the effects of vibration frequency and intensity input. Transition to a vibro-fluidized state at a critical dimensionless vibration acceleration is characterized by dramatic decreases in vane power, dynamic zero-shear rate torque and measurable density fluctuations throughout the bed. In the vibro-fluidized state, the vane power and extrapolated zero-shear rate torque are weakly influenced by the vibration force and frequency. The measured vane power becomes invariant with bed height above a critical bed aspect ratio. This phenomenon can be characterized by the Janssen equation, which relates static pressure to the height of the granular media.