As the water content is reduced the soil becomes stiffer and starts developing resistance to shear deformation.  A soil containing very high water content is offers no shearing resistance and can flow like liquids. Primarily for soil identification and classification.

INTRODUCTION  The liquid and plastic limits have been widely used all over the world. Cohesion Limit: It is that moisture content which soil just sticks metal surface such as spatula blade. Sticky Limit: It is that moisture content which soil crumbles just stick together. Shrinkage Limit (SL,W S ) : It is the water content at which the soil stops shrinking further and attains a constant volume. Plastic Limit (PL, W P ) : It is the water content at which the soil just fails to behave plastically. Liquid Limit (LL, W L ) : It is the water content at which the soil on a verge (border) to become viscous fluid. The water contents at which the soil changes from one state to another are known as consistency limits or Atterberg’s limits as shown in Fig.(1). 4 1 ATTERBERG LIMITS DEFINITION Atterberg a Swedish agricultural scientist (1911) developed a method to describe the consistency of fine-grained soils with varying moisture content, and he proposed five “limits” for fine-grained soils with varying water content. The average water content to the nearest whole number should be reported.Lab. The plastic limit should be determined for at least three portions of the soil passing through 425μm IS Sieve. V) Repeat the process at least twice more with fresh samples of plastic soil each time. Iv) Collect and keep the pieces of crumbled soil thread in the container used to determine the moisture content. Iii) Repeat the process of alternate rolling and kneading until the thread crumbles.

Reduce the water content and roll it into a thread again. of the threads can be reduced to less than 3mm, without any cracks appearing, it means that the water content is more than its plastic limit. The rate of rolling should be between 80 to 90 strokes per minute to form a 3mm dia. I) Take about 8g of the soil and roll it with fingers on a glass plate. Mix the soil with distilled water in an evaporating dish and leave the soil mass for naturing. Take out 30g of air-dried soil from a thoroughly mixed sample of the soil passing through 425μm IS Sieve. and about 10cm long PREPARATION OF SAMPLE: Iii) Container to determine moisture content I) Porcelain evaporating dish about 120mm dia. It begins to crumble when rolled into threads of 3mm dia. The plastic limit of fine-grained soil is the water content of the soil below which it ceases to be plastic.

To determine the plastic limit of soil as per IS: 2720 (Part 5) – 1985.

Plastic limit test