Bulking of sand is the phenomenon in which the volume of sand increases, mainly due to capillary action or adding some specific value of water content (ex- 4-5%) to dry sand.

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%

Slaking of clay 

basically, Dry the clay soil below it shrinkage limit. then you suddenly immersed these clay to water,

rear phenomena happen, in which clay suddenly mix (not properly mix like salt and water) with water and clay particles is all around in the water,

this phenomenon called slaking of clay. See fig for better understanding.

If you compare it with plastic clay and clay contain some amount of moisture,

these type of clay not immediately mix in water.