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To Determine Liquid Limit of Soil & Plastic Limit of Soil 

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Apparatus


Related Pages  Significance and UseThis testing method is used as an integral part of several engineering classifications systems to characterize the fine‑grained fractions of soils and to specify the fine‑grained fraction of construction materials. The liquid limit, plastic limit and plasticity index of soils are also used extensively, either individually or together, with other soil properties to correlate with engineering behavior such as compressibility, permeability, compactibility, shrink‑swell and shear strength.
This test method covers the determination of the liquid limit, plastic limit and plasticity index of soils. The liquid and plastic limits of soils are often referred the as the Atterberg limits.  
Procedure for Liquid Limit TestSee Also: Definition of Liquid Limit  Background of Liquid Limit Test.
Note: The liquid limit is the water content at which it will takes 25 blows to close the groove over a distance of 13 mm. Run at least five tests increasing the water content each time. As the water content increases it will take less blows to close the groove. Observations & Calculations:
Plot the relationship between the water content, w, and the corresponding number of drops, N, of the cup on a semi‑logarithmic graph with water content as the ordinates and arithmetical scale, and the number of drops on the abscissas on a logarithmic scale. Draw the best fit straight line through the five or more plotted points. Take the water content corresponding to the intersection of the line with the 25 drop abscissa as the liquid limit, LL, of the soil. GraphFollowing is the graph of relation between water content and number of blows Precautions
Applications
Limitations of Liquid Limit TestProcedure for Determination of the Plastic LimitSee Also: Definition of Plastic Limit
Note: Repeat this procedure three times to compute an average plastic limit for the sample. Calculations
Compute the average of the water contents obtained from the three plastic limit tests. The plastic limit, PL, is the average of the three water contents.
Calculate the plasticity index as follows: PI = LL ‑ PL where: LL = liquid limit, and PL = plastic limit. Precautions
Observations and calculations:
Average plastic limit = (1.13 + 1.7)/2 =1.15%  
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