A SOIL BEHAVING ESSENTIALLY AS A CLAY, HAVING AN APPRECIABLE PROPORTION OF SAND OR SILT IS REFERRED TO AS A SANDY CLAY OR SILTY CLAY

Clay is usually recognized by its sticky and plastic properties and spacial odour. Clay particles in pure state are soluble in water, or remain as mechanical mixture in suspension in a colloidal state and gradually settle down at bottom in the form of stiff paste. When dry, clay forms hard lumps which can not be broken down and powdered between the fingers, while lumps of silts can readily be broken down and powdered. Difference between clay and silt is not only based on the grain particle size but on the plasticity and shear strength.'Fat' clays are highly plastic and 'lean ' clays are moderately plastic. Colour of clay may be black, white, red or yellow. For many Engineering purposes a perfectly pure clay would be useless as it might be of so fine a texture and so highly plastic that it would shrink excessively on drying. Clay is very absorbent and can swell to double its volume. Clay tends to hold free water in addition to their adhered water and do not drain nor do they dry out rapidly. Clays are subject to a large amount of shrinkage from loss of moisture which may be due to evaporation or transpiration from vegetation. Shrinkage in clays also results from external loadings (or consolidation) as under load the moisture in clay is forced out, and which can be forced out more rapidly if it is mixed with sand. Some clays lose their shear strength considerably when their structure is disturbed, such clays have a low liquid limit. Natural clay deposits may contain up to 70 percent or even more of material belonging to the sand and silt grades. A soil behaving essentially as a clay, but having an appreciable proportion of sand or silt is referred to as a sandy clay or silty clay:-- Er Fateh chand Guleria, RTI welfare Association registered number HPCD, 3552 , Bilaspur Himachal Pradesh phone number, 9459334377