What Are Atterberg Limits Test? | Uses of Atterberg Limits Shrinkage Limit | Liquid Limit | Plastic Limit
What Are Atterberg Limits Test? | Uses of Atterberg Limits Shrinkage Limit | Liquid Limit | Plastic Limit
What Are Atterberg Limits?
Atterberg Limits is a set of tests used in geotechnical engineering to test the particle size of soil aggregates.
It is a basic indicator of a fine-grained soil’s essential water content: its shrinkage limit, plastic limit, and liquid limit.
The idea is that the soil will behave differently when wet and dry, this can help to identify the soil type.
A soil can occur in one of 4 stages depending on its water content: solid, semi-solid, plastic, or liquid. The consistency and behavior of a soil differs in each condition, as do its physical properties.
As a result, the boundary between each state can be determined based on a change in the behavior of the soil.
The tests are often performed as a sequence of steps to provide a more accurate result and these steps are:
• The liquid limit is the point at which the soil changes from freely flowing to a dough-like material.
• The plastic limit is the point at which the soil changes from a paste-like material to a viscous liquid.
• The shrinkage limit is the point at which the soil changes from a rubber like material to a viscous liquid.
• The swelling of clay is defined as the amount of water it takes to make the soil’s volume swell.
The Atterberg limits can be used to differentiate between silt and clay, as well as distinct types of silts and clays.
The water content at which soils transition from one state to another is referred to as the consistency limit or Atterberg’s limit.
History of Atterberg Limits
Albert Atterberg, a Swedish chemist and agricultural scientist, was the first to identify the boundaries of soil consistency for the classification of fine-grained soils in 1911.
discovered that plasticity is a distinguishing feature of cohesive (clay and silt) soils and proposed classifying soils with particle sizes of 2m (0.002mm) or less as clays.
In the early 1930s, Karl Terzhagi and Arthur Casagrande recognized the need of defining soil plasticity for use in geotechnical engineering applications.
Casagrande improved and standardized the experiments, and his methods are still used to measure the liquid, plastic, and shrinkage limits of soils.
Soil characteristics are used to evaluate soils that will have structures constructed on them. When wet, soils hold water and some expand in volume (smectite clay).
The extent of expansion is proportional to the soil’s ability to absorb water and its structural make-up (the type of minerals present: clay, silt, or sand).
These tests are mostly performed on clayey or silty soils because they stretch and shrink when the moisture content changes.
Because clays and silts mix with water easily, their sizes and shear strengths fluctuate.
For this reason, these tests are commonly applied in the preliminary stages of planning any structure to check that the soil has the appropriate amount of shear strength and does not change volume excessively as it expands and shrinks with varying moisture levels.
Importance of Atterberg Limits Test
Geotechnical engineers must examine soils intended to support structures, pavements, or other loads in order to forecast their behavior under applied stresses and changeable moisture conditions.
Soil mechanics experiments in geotechnical laboratories assess particle size distribution, shear strength, moisture content, and the possibility for cohesive soil expansion or shrinkage.
The moisture contents at which fine-grained clay and silt soils transition between solid, semi-solid, plastic, and liquid states are determined through Atterberg limits experiments.
Shrinkage Limit
The shrinkage limit (SL) is the water content at which the soil transitions from semi-solid to solid.
With additional drying of the material, the volume of the soil mass ceases to change at this moisture content.
Shrinkage limits are adopted rather less frequently than liquid and plastic limits.
Liquid Limit
The liquid limit (LL) is the water content at which soil transitions from a plastic to a liquid state when the soil specimen is just fluid enough to close a groove when jolted in a specific manner.
Plastic Limit
The water concentration at the transition from a plastic to a semi-solid state is referred to as the Plastic Limit (PL). This test is repeatedly wrapping a soil sample into a thread until it crumbles.
Atterberg Limits FAQs
1. What is the purpose of Atterberg limits?
The purpose of Atterberg limits is to show you how individual soils change from one state to another. This will help to identify the soil type and its most stable state.
2. What are Atterberg limits?
Atterberg limits is a set of tests used in geotechnical engineering to test the particle size of soil aggregates.
Soil characteristics are used to evaluate soils that will have structures constructed on them. When wet, soils hold water and some expand in volume (smectite clay).
It will help to identify the different states that a soil can exist in (solid, semi-solid, plastic, or liquid) based on its water content.
3. Are there different types of Atterberg limits?
There are different types of Atterberg limits depending on the type of test:
• The shear strength limit is the point at which the soil changes from elastic to plastic, or from plastic to viscous. This is determined by the soil’s shear strength.
• The liquid limit is the point at which the soil changes from freely flowing to a dough-like material.
• The plastic limit is the point at which the soil changes from a paste-like material to a viscous liquid.
• The shrinkage limit is the point at which the soil changes from a rubber like material to a viscous liquid.
4. How do the different types of Atterberg limits work?
The different types of Atterberg limits work in the same way. The soil performs a series of tests, depending on its type, to determine whether it can be classified as solid or semi-solid.
• The liquid limit is the point at which the soil changes from freely flowing to a dough-like material.
• The plastic limit is the point at which the soil changes from a paste-like material to a viscous liquid.
• The shear strength limit is the point at which the soil changes from elastic to plastic, or from plastic to viscous.
5. What are the different types of Atterberg limits?
The different types of Atterberg limits are as follows:
• Shear strength: When a material breaks, it will deform under pressure and change volume. In this state, there is no permanent deformation. This is commonly used to identify how a soil will behave when loaded.
• Liquid limit: The liquid limit is the point at which the soil changes from freely flowing to a dough-like material.
• Plastic limit: The plastic limit is the point at which the soil changes from a paste-like material to a viscous liquid.
• Shrinkage or shrink/swell: This test indicates if the solid particles in the soils can change volume with changing moisture levels.
6. What are the three 3 Atterberg limits?
There are three important Atterberg limits: shrinkage limit (SL), plastic limit (PL), and liquid limit (LL).
The shrinkage limit is the water content at which the volume of the soil starts to increase.
The plastic limit (PL) is the water content at which the material starts showing plasticity.
The liquid limit is the water content at which the material will flow like a liquid.
7. How do I determine test results for Atterberg limits?
To determine test results for Atterberg limits, you need to know the soil’s grain size distribution. You can then use a table or chart to find out the Atterberg limits of that soil type.
8. What is plastic limit?
In a standard test, the plastic limit is the water content at which a soil-water paste transforms from a semisolid to a plastic consistency when rolled onto a 3.175-mm (1/8-inch) diameter thread.
9. What is shrinkage limit?
In a standard test, the shrinkage limit is the water content at which the volume of the soil starts to increase, and expands when it is rolled onto a 3.175-mm (1/8-inch) diameter thread.
10. Where is shrinkage limit useful?
This limit is required for investigations into the swelling and shrinkage properties of cohesive soil.
The shrinkage factor contributes in the construction of structures composed of or resting on this soil.
It aids in identifying the suitability of soil as a building material for foundations, roadways, embankments, and dams.
11. What is plasticity index?
A soil’s plasticity index is the numerical difference between its liquid and plastic limits, and it is a dimensionless number. Moisture content is a factor in both the liquid and plastic limits.
12. How are Atterberg limits calculated?
Atterberg soil indexes mathematically compare test values to indicate distinct plasticity and consistency qualities.
Plasticity index calculated
The plasticity index (PI) is defined as the difference between the liquid and plastic limits (PI = LL-PL). Soils with a high PI tend to be clay, those with a low PI likely to be silt, and those with a plasticity index of 0 (non-plastic) tend to be devoid of silt or clay.
Plasticity Index = Liquid Limit – Plastic Limit
Liquidity Index (LI) Formula
The liquidity index (LI) is calculated by subtracting the plastic limit from the sample’s natural water content and dividing by the plasticity index. Soils having a Liquidity Index of 1 or higher are closer to liquid. A Liquidity Index (LI) of 0 or lower implies that the soil is tougher and brittle. The Liquidity Index predicts soil qualities at various moisture levels.
LI = (PL − Natural Water Content) ÷ PI
Soil Formula Consistency Index (CI)
The consistency index (PI) is calculated by dividing the liquid limit of the soil minus the natural moisture content by the PI. It is related to the LI and serves as a measure of relative shear strength. As CI grows, so does the soil’s stiffness or shear strength.
CI = (LL − Natural Moisture Content) ÷ PI
13. Where are Atterberg limits most commonly used?
Atterberg limits are the most common location for moisture content tests, especially for assessing soils that cannot be compacted into a benchtop laboratory.
can also be used in different industries that require information about the soil’s behavior when placed under stress.
