Effect of Eccentricity and Boundary on Jet Formation of Soft Fine Sand

Abstract

Very soft fine quartz sand is prepared in a fully decompactified state by using a sieve. After flattening the sand surface, a steel ball is dropped on the sand bed. On impact of the steel ball, fine soft sand is blown away in all directions and a transient impact crater forms. In the process of splashing, the soft sand surface first rises and then falls under the function of surface wave and air pressure. When the sand surface falls, a granular jet emerges and is driven straight into the air. After reaching the highest point, the jet goes downwards into the soft sand, thus leaving a central sand pile on the ground. Then, after a while, the air bubble beneath the sand horizontal level rises slowly towards the surface, causing a granular explosion. In addition, the eccentricity of falling point, lateral boundary material and gas permeability of bottom boundary are changed to investigate the influence on the formation of the jet.