Measurements of velocity and pressure of a collapsing granular pile

This paper proposes a synchronized measurement method of analyzing collapsing granular piles using a highspeed camera and a grid-based tactile pressure sensor. The method is developed with a pressure sensor comprising 2016 individual sensels and a granular pile consisting of approximately 24,000 ceramsite spheres. Geometric, kinetic, and mechanical quantities (i.e., packing fraction phi, mean speed (nu) over bar, and pressure P) are simultaneously measured for a more detailed analysis of collapse processes. Collapses last for about 33T(C). where the characteristic time T-C = root h(0)/g, h(0) is the initial height of the granular pile, and g is acceleration due to gravity. The failure angle is measured as phi(f)approximate to 51 degrees. The relation between packing fraction and flow speed in mu(I) rheology, which is a previous theoretical predication, is validated in the experimental measurements of this work. Pressure distributions beneath the granular pile are recorded in time. Results show that the probability density function of the scaled contact pressure exhibits the power-law for small stresses, whilst a Gaussian distribution for large pressures beneath the granular pile at the initial state. As the pile is agitated, a large drop in pressure is observed during the stage when many particles fall freely, and pressure propagation is compared with mean speed. (C) 2016 Elsevier B.V. All rights reserved.