Atterberg Limits Of Soil Analysis

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3.0 DETERMINATION OF CONSISTENCY LIMITS OF A SOIL

3.1 Introduction
3.1.1 Objective
To determine the Atterberg Limits of Soils
3.1.2 Learning Outcomes
Understand the Principle of Consistency and Atterberg Limits of Clay Soils
Describe the Atterberg Limit Tests and their uses
Perform the tests and obtain the Atterberg Limits
Calculate some Indices (Flow Index, Plasticity Index and Toughness Index) for the Clay Soil

3.1.3 Consistency indices
Fine-grained soils are formed in nature by the gradual deposition of soil particles from suspension in water. In the process of settlement, consolidation and drying out, the material passes through several well-defined states, namely: liquid suspension; viscous liquid; plastic solid; semi- plastic solid;
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Find the relationship between water content and number of blows
3. Draw flow curve
4. Determine the liquid limit
3.2.2 NEED AND SCOPE
The Liquid Limit is an important parameter that can be used to understand the stress history and general properties of the soil on the construction site. It can be used to estimate the compression index of a soil which is used in settlement analysis If the natural moisture content of soil is close to liquid limit, the soil can be considered as soft; if the moisture content is less than the liquid limit, the soil can be considered as stiff; however if the moisture content is much less than liquid limit, the soil may become brittle and stiffer.
3.2.3 Principle
The Liquid Limit (LL) is the boundary between the liquid and plastic states of a soil. It is the minimum moisture content at which the soil will flow under its own weight. As obtained from the standard test, it is defined as the water content at which a trapezoidal groove of specified shape (12.5 mm) cut in moist soil, held in a special cup, is closed for 10 mm of its length after 25 taps on a hard rubber plate. The liquid limit is directly proportional to the compressibility of the soil. At this limit the soil possesses low shear

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