Experimental realization of incipient active failure in sand heap by seismic loading

Abstract

Sand heaps avalanche when a static angle of repose is exceeded, and freeze at a dynamic angle of repose. The stress distribution in a planar sand heap stabilized at the angle of repose with an incipient active failure condition, by which the material is on the verge of failure everywhere, was examined. At the time of construction, the vertical pressure was initially not in the incipient failure. A slight amount of seismic loading using the sinusoidal motions of a shaking table was set up with just enough energy to rearrange the sand particles, to erase the formation history, and to fluctuate local density inside a sand heap without an excessive loss of mass. During the experiments, laser displacement sensors and pressure gauges were employed to monitor the vertical displacements above and the vertical pressures below the sand heap respectively. The non-linear differential equations, characterizing the stress distribution in an active sand heap, were formulated under the Mohr–Coulomb failure criterion and numerically solved by the Newton method. Bulk solids started flowing after the state of incipient failure; therefore, the experimental vertical pressure profiles were found to gradually conform to the theoretical vertical pressure profiles if the sand heap was subjected to sufficient excitation.