liquid limit and plastic limit test of soil pdf

Liquid limit and plastic limit test of soil pdf

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The authors would like to thank the discusser for his interest in their paper and for his contributions on the mechanisms taking place within the plastic limit test. This, however, depends on the purpose for which a plasticity index is required. While both equations 14 and 15 are statistically significant, it could be argued that these correlations would improve if a plastic limit value based on a strength criterion were available rather than the current one based on ductility.

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The Atterberg limits are a basic measure of the critical water contents of a fine-grained soil : its shrinkage limit , plastic limit , and liquid limit. Depending on its water content , a soil may appear in one of four states: solid, semi-solid, plastic and liquid.

In each state, the consistency and behavior of a soil is different and consequently so are its engineering properties. Thus, the boundary between each state can be defined based on a change in the soil's behavior. The Atterberg limits can be used to distinguish between silt and clay , and to distinguish between different types of silts and clays. The water content at which the soils change from one state to the other are known as consistency limits or Atterberg's limit.

These limits were created by Albert Atterberg , a Swedish chemist and agronomist in Distinctions in soil are used in assessing the soils that are to have structures built on them. Soils when wet retain water, and some expand in volume smectite clay. The amount of expansion is related to the ability of the soil to take in water and its structural make-up the type of minerals present: clay , silt , or sand. These tests are mainly used on clayey or silty soils since these are the soils that expand and shrink when the moisture content varies.

Clays and silts interact with water and thus change sizes and have varying shear strengths. Thus these tests are used widely in the preliminary stages of designing any structure to ensure that the soil will have the correct amount of shear strength and not too much change in volume as it expands and shrinks with different moisture contents.

The shrinkage limit SL is the water content where further loss of moisture will not result in more volume reduction. The shrinkage limit is much less commonly used than the liquid and plastic limits. The plastic limit PL is determined by rolling out a thread of the fine portion of a soil on a flat, non-porous surface. If the soil is at a moisture content where its behavior is plastic, this thread will retain its shape down to a very narrow diameter.

The sample can then be remolded and the test repeated. As the moisture content falls due to evaporation, the thread will begin to break apart at larger diameters. The plastic limit is defined as the gravimetric moisture content where the thread breaks apart at a diameter of 3. A soil is considered non-plastic if a thread cannot be rolled out down to 3.

The liquid limit LL is conceptually defined as the water content at which the behavior of a clayey soil changes from the plastic state to the liquid state. However, the transition from plastic to liquid behavior is gradual over a range of water contents, and the shear strength of the soil is not actually zero at the liquid limit. The precise definition of the liquid limit is based on standard test procedures described below.

A groove was cut through the pat of clay with a spatula, and the bowl was then struck many times against the palm of one hand. Casagrande subsequently standardized the apparatus and the procedures to make the measurement more repeatable. Soil is placed into the metal cup Casagrande cup portion of the device and a groove is made down at its center with a standardized tool of 2 millimetres 0.

The number of blows for the groove to close is recorded. The moisture content at which it takes 25 drops of the cup to cause the groove to close over a distance of The test is normally run at several moisture contents, and the moisture content which requires 25 blows to close the groove is interpolated from the test results. Another method for measuring the liquid limit is the fall cone test , also called the cone penetrometer test. It is based on the measurement of penetration into the soil of a standardized stainless steel cone of specific apex angle, length and mass.

Although the Casagrande test is widely used across North America, the fall cone test is much more prevalent in Europe and elsewhere due to being less dependent on the operator in determining the liquid limit. The values of these limits are used in a number of ways. There is also a close relationship between the limits and properties of a soil such as compressibility , permeability , and strength. This is thought to be very useful because as limit determination is relatively simple, it is more difficult to determine these other properties.

Thus the Atterberg limits are not only used to identify the soil's classification, but it allows for the use of empirical correlations for some other engineering properties. The plasticity index PI is a measure of the plasticity of a soil.

The plasticity index is the size of the range of water contents where the soil exhibits plastic properties. Soils with a high PI tend to be clay, those with a lower PI tend to be silt, and those with a PI of 0 non-plastic tend to have little or no silt or clay.

Soil descriptions based on PI: [8]. The liquidity index LI is used for scaling the natural water content of a soil sample to the limits. The consistency index Ic indicates the consistency firmness of a soil. That means soil is in the liquid state. More over, sum of Liquidity index and Consistency index equal to 1 one. The curve obtained from the graph of water content against the log of blows while determining the liquid limit lies almost on a straight line and is known as the flow curve.

Where 'I f is the slope of flow curve and is termed as "Flow Index" [9]. The shearing strength of clay at plastic limit is a measure of its toughness. It is the ratio of plasticity index to the flow index. It gives us an idea of the shear strength of soil. The activity of a soil is the ratio of plasticity index to the clay size fraction.

If activity is less than 0. If activity exceeds 1. If activity lies within the above values then the soil is moderately active. From Wikipedia, the free encyclopedia. Geotechnical characteristics of a soil related to its water content.

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Forces Effective stress Pore water pressure Lateral earth pressure Overburden pressure Preconsolidation pressure.

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Contents [ hide show ]. The consistency and behavior of a clayey soil is different as are the engineering properties at varying degrees of moisture content. Thus, the boundary between each state can be defined based on a change in the clay's behavior. Swedish scientist Albert Atterberg was the first person to define the limits of soil consistency for the classification of fine-grained soils and later, they were refined by Arthur Casagrande. Depending on the water content of a soil, the soil may be in one of four states: solid, semi-solid, plastic and liquid. The Liquid Limit LL or w LL , also known as the upper plastic limit, is the water content at which the soil changes from the liquid state to a plastic state. It is the minimum moisture content at which a soil flows upon application of very small shear force.

Soils intended to support structures, pavements, or other loads must be evaluated by geotechnical engineers to predict their behavior under applied forces and variable moisture conditions. Soil mechanics tests in geotechnical laboratories measure particle size distribution, shear strength, moisture content, and the potential for expansion or shrinkage of cohesive soils. Atterberg limits tests establish the moisture contents at which fine-grained clay and silt soils transition between solid, semi-solid, plastic, and liquid states. In , Swedish chemist and agricultural scientist Albert Atterberg was the first person to define the limits of soil consistency for the classification of fine-grained soils. Karl Terzhagi and Arthur Casagrande recognized the value of characterizing soil plasticity for use in geotechnical engineering applications in the early s. Casagrande refined and standardized the tests, and his methods still determine the liquid limit, plastic limit, and shrinkage limit of soils.

Undrained shear strength of a soil at the liquid limit water content can be considered to be around 1. Plasticity index of soils has been defined by one school of thought as a range of water content producing a fold variation in their undrained shear strength. The undrained shear strength-water content relationship has been found to be linear in the log—log plot for a wide range of water contents beginning from around the plastic limit to near the liquid limit. Normalization of undrained shear strength—water content relationship in a log—log plot has led to the conclusion that the water content at the liquid limit and at the plastic limit, obtained by cone penetration, could also be uniquely related. This contradicts the original understanding of Atterberg limits, namely liquid and plastic limits which are two independent parameter not related at all. Undrained shear strength of a soil from water content around the liquid limit to water content around the plastic limit can be determined by the fall cone test.

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The Atterberg limits are a basic measure of the critical water contents of a fine-grained soil : its shrinkage limit , plastic limit , and liquid limit. Depending on its water content , a soil may appear in one of four states: solid, semi-solid, plastic and liquid. In each state, the consistency and behavior of a soil is different and consequently so are its engineering properties. Thus, the boundary between each state can be defined based on a change in the soil's behavior. The Atterberg limits can be used to distinguish between silt and clay , and to distinguish between different types of silts and clays.

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2 comments

  • Melanie C. 06.05.2021 at 09:08

    Organic soils in particular undergo changes as a result of oven-drying or even extended air-drying. Other soils containing clay may agglomerate, lose absorbed.

    Reply
  • Centola L. 12.05.2021 at 05:41

    Determination of Plastic Limit is as important as Liquid Limit so as to ascertain Plasticity Index, Ip of the soil. The plastic limit of a soil is the moisture content.

    Reply

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