The researchers tested different densities of sand to see how it affects its strength and behavior under stress. They found that denser sand is less squishy and can handle more pressure before changing shape. Denser sand also expands less and has less negative pressure when squeezed. The angle at which the sand starts to slide is higher when it's denser. In tests where the sand was squeezed from all sides, it compressed more and broke at a lower point compared to tests where it was squeezed from just two sides.