we know sand is not plastic in nature, assuming dry sand placed on the ground where the capillary action occurred.
Due to this action water start uplift throw sand particle. and the sand becomes damp.
in this damp sand, cohesion(attraction of water molecule) develop throwout capillary rice.
this attraction prevents sand particle to taking a stable position. because in the previous lesson we know capillary water produced upward pressure.
from the all above definition we say the volume of the sand increase due to damping, this increased volume is called bulking of sand.
also, note that if you increase more water than a reasonable amount,
capillary action destroyed and volume decrease.
you can check bulking of sand at home by adding some water to sand,
bulking is maximum at water content around 4-5%