The purpose of this lab experiment is to classify soil using two testing methods, which are Mechanical Sieve (ASTM D6913), and Hydrometer (ASTM D7928). Different classes of soil behave very differently. So classifying a soil enables engineers to understand possible failure mechanisms and corresponding design methodologies.
Liquid limit(LL) is the moisture content between liquid and plastic states. It is the water content at which a pat of soil cut by a groove in the casa grande apparatus, requires 25 blows to flow together for a distance of 13 mm (1/2 inch).
Plastic limit(PL) is the state changes between plastic and semi-solid. It is defined as the moisture content at which a thread of soil will just crumble when rolled to a diameter of 1/8 in. (3.2mm).
It is important to know the liquid limit and plastic limit of the soil to classify fine grained soil and toughness of the soil.