Atterberg Limit

Topics: Arthur Casagrande, Atterberg limits, Soil tests Pages: 7 (2039 words) Published: May 26, 2013
This report is to establish the Atterberg limit of s oil sample after performing and analyzing the tests performed in laboratory. Atterberg limit is used to differentiate between silt & clay , in various categories, and also to establish boundaries between each state of soil, i.e soild, semi-solid, plastic & liquid, and the change in soil behavior. The method of Cone Penetrometer was used to determine the Liquid and Plastic limits of given soil sample. The objective of this test is to derive Plastic and Liquid limits from the results and classify the composition of the soil. The variation in composition of various soils can determine the effect on Atterberg Limit and understanding the plasticity of the soil is of vital importance as it has significance in any project. Background Information:

The Atterberg Limits determines the plastic limits , the water content where soil starts to exhibit plastic behavior, and the liquid limits, where the water content of soil changes from plastic to liquid behavior. These limits are used to determine the consistency of a soil composition at various water content values. The method used to determine the Liquid limit is verified to derive accurate measurement. The Cone Penetrometer test is performed for Liquid Limit in laboratory, Casagrande device method is not described in this report. Generally, in falling cone penetrometer test, the depth of penetration of the cone is measured and a curve of cone penetration against moisture content is produced. Liquid Limit is the moisture content at which the cone penetrates the soil by 20 mm and The Plastic Limit of the samples is found by rolling smaller specimens repeatedly until the specimen breaks at 3.18mm diameter. The water content at this point is the Plastic Limit of the specimen. The theory behind the test is that as the specimen is rolled down, some of the water in the soil specimen dissipates until the specimen breaks off. Since soil in its plastic state deforms without cracking, the point when the specimen does crack determines the moisture content just gone below its plastic limit. Purpose:

The purpose of this test is to determine the Atterberg Limits to classify the type of soil with consistency at different moisture contents. And cracking and deformation of soil at different stages.

It is assumed in the theory that in Cone Penetrometer test the cone has to be lowered to touch the soil surface and then released. The soil reaches its liquid lit when it penetrates the soil by 20mm and this step is repeated atleast four times. As far as Plastic limit is concerned it is mandatory the soil should not crack before reaching the diameter of 3mm, if it does so more water should be added keeping in mind that to add the water in controlled quantity as adding much water can ruin the soil sample.

Liquid Limit:
The test procedure is as follows:
1. At least 250 g of the material passing the 425 µm sieve was obtained and prepared in accordance with AS 1289.1.1. Alternatively, all soil that passed a 425 µm sieve may be used in the natural state without further preparation. 2. The sample was placed in the mixing bowl or on the glass plate and water was added in increments, mixed thoroughly with the palette knives for not less than 3 min after each increment of water. 3.Water was added and mixed until the soil became a thick...
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