A pile of sand with water content of 10 is placed next to a

A pile of sand with water content of 10% is placed next to a pile of clay soil with exactly the same water content. If water flow between two soils is allowed, please indicate the water flow direction (i.e. sand to clay, or clay to sand, or no water flow) and present your reason

Solution

Flow will be from sand to clay, because the void ratio or void space in clays is large when compared with sand. The reason is the micro-structure of the clay, and therefore it has a larger water holding capacity. Also the pores are generally not interconnected, and therefore the water is not free to move out.

On the other hand, the water in the sand is loosely held and can move under the effect of gravity alone.