Sand has a natural tendency to segregate. When sand is dropped into the center of a bin, the larger particles will move to the sides of the bin. The smaller particles will remain in the center. The wider the grain size distribution in the sand, the greater the tendency to segregate.
Single discharge bins create last sand in, first sand out, commonly called rat-holing. Multiple discharge openings in the bottom of the bin promote even drainage. Variations in grain size distribution may result in variations in mold strength and permeability.