how to distinguish silt and clay from atterberg

At certain moisture contents a soil that contains appreciable quantities of clay can be deformed and remolded in the hand without disintegration. The property of plasticity is characteristic of clays and may be used as the basis for a simple field test. The reaction is described as rapid, slow or none. Usually, the greater the proportion of clay in the sample, the slower the reaction to the test. Then if the soil pat is deformed, in some instances by squeezing and in others by stretching, the water flows back into it and leaves the surface with a dull appearance. If the soil is silty, water rises quickly to its surface and gives it a shiny or glistening appearance. The back of the hand is then lightly tapped. In this test a small amount of soil is mixed with water to a very soft consistency in the palm of the hand. Since silts are considerably more permeable than clays, the dilatancy or shaking test may also be used to distinguish between the two materials. A clay fragment can be broken only with great effort, where as a silt fragment crushes easily. The effort required to break the fragment provides a basis for describing the strength as ver low, low, medium, high or very high. It is then broken and a small fragment about 1.0 cm in size is pressed between thumb and forefinger. A small briquette of the soil is molded and allowed to dry in the air. The dry strength provides one basis for distinction. Let us discuss each one of them one by one. There are 4 nos of field test that we can easily conduct on the field to identify silt & clay. Furthermore, since both are microscopic, physical properties other than particle size must be used as criteria for field identification. The distinction between silt & clay cannot be based on particle size because the significant physical properties of the two materials are related only indirectly to the size of particles.

How to distinguish silt and clay from atterberg