Explanation

1. Dispersive clays are a particular type of soil material in which the clay fraction erodes in the presence of water by a process of de-flocculation. This de-flocculation occurs when the interparticle forces of repulsion exceed those of attraction so that the clay particles go into suspension, and if the water is flowing, as in a crack in an earth embankment, the detached particles are carried away and piping occurs.

2. Expansive clay is clay soil that is prone to large volume changes (swelling and shrinking) that are directly related to changes in water content. Soils with a high content of expansive minerals can form deep cracks in drier seasons or years; such soils are called vertisols.

3. Varved clay is a clayey sedimentary soil, formed in glacier lakes, with visible layering.

• It is composed of two periodically repeated layers: dark (silty-clayey) and bright (silty-sandy) ones.
• During warm periods, when the glacier was melting, deposits were carried into the lake where coarser particles were deposited and composed light varves. In cold periods, when the lake was frozen, fine particles precipitate forming dark varves