Progressive pressure measurements beneath a granular pile with and without base deflection

This paper describes an experimental investigation to measure the pressure distribution underneath a conical pile of granular material as the pile grows. Several factors have been suggested to explain the pressure dip observed under the apex of a pile but the relative significance of these factors is far from clear. This study was conducted using quite round rough particles in a relatively large scale experiment to avoid the possibility that particle scale effects would mask the macroscopic pressure distribution. A reproducible pressure profile with a significant central dip was observed in each test, which confirms that at macroscopic scale, the pressure dip is a stable and robust phenomenon when the pile is formed from a localised jet. The normalised data provide quantitative information on the vertical force redistribution away from the central zone. The results also show that base deflection is not a prerequisite for the pressure dip, but that it enhances both the magnitude and the width of the dip.