This is simple test which is used in the field for rough classification of soil.
i) The prepared soil sample is completely dried in the sun or by air drying. Its strength is tested by breaking between the fingers.
ii) Dry strength or resistance to breaking is a measure of plasticity and is considerably induced by the colloidal fraction content of the soil.
iii) If the dry sample can be easily powered, it is said to have low dry strength, whereas, if considerable finger pressure is required to break the lumps, it is said to have a medium dry strength and if it cannot be powdered at all, it is said to have a high dry strength
iv) Dry strength is characteristics of clays of high plasticity. Typical inorganic silts have only a slight dry strength. Silty fine sand and silts have practically the same low dry strength but can be distinguished from each other by their feel during powdering of the dry sample.
Dilatancy Test
This is also a simple test used in the field for rough classification of soil.
i) A 5 cm3 of soil sample is taken and enough water is added to nearly saturate it. The part of soil is placed in the open palm of the hand and shaken horizontally, striking rigorously against the other hand several times.
ii) The pat is then squeezed between the fingers. The appearance and disappearance of water with shaking and squeezing is reffessed to as a positive reaction.
iii) The reaction is called quick, if water appears and disappears rapidly. It is called slow, if water appears and disappears slowly and no reaction if water does not appear.
iv) The type of reaction is observed and recorded; inorganic soils exhibit a quick reaction whereas clays exhibit known to slow.