How do the strength and the cohesion of clay-rich regolith or soil change with the addition of water?

Water lowers the strength and cohesion of clay-rich regolith or soil.

Explanation:

Water can seep into the soil or clay-rich regolith and replace the air in the pore space of the soil or regolith. Water will completely surrounds all the grains of the clay-rich regolith and breaks the bonds in between the grains, that is eliminating all grain to grain contact of the regolith. When the regolith becomes saturated with water, the angle of repose is reduced to very small values and the regolith tends to loose its form.