Encyclopedia of Engineering Geology

2018 Edition
| Editors: Peter T. Bobrowsky, Brian Marker

Plasticity Index

  • Jeffrey R. KeatonEmail author
Reference work entry
DOI: https://doi.org/10.1007/978-3-319-73568-9_223


The plasticity index ( PI) is calculated as the numerical difference between the liquid limit ( LL) and plastic limit ( PL); PI = LLPL. These three parameters collectively are the Atterberg limits (ASTM 2010). The liquid limit and the plasticity index are the axes of the plasticity chart (Fig. 1), which is used in engineering to classify fine-grained soils, which are defined as soils with 50% or more passing the #200 sieve (ASTM 2011). The #200 sieve has 200 openings per inch, or 200 openings per 25.4 mm, with 0.074-mm openings (ASTM 2009). Particles that pass through a #200 sieve are classified as fine-grained (silt, clay), and typically referred to as “fines,” whereas particles that are retained on a #200 sieve are classified as coarse-grained (sand, gravel, cobbles, boulders). The Atterberg limits test also is performed on the matrix of coarse-grained soils, which is the fraction of a soil sample that passes the #40 sieve (0.42-mm diameter openings; medium sand size and...
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  1. ASTM (2009) Standard test methods for particle-size distribution (gradation) of soils using sieve analysis. American Society for Testing and Materials Test D6913-04(2009)e1. http://www.astm.org/Standards/D6913.htm. Accessed April 2016
  2. ASTM (2010) Standard test methods for liquid limit, plastic limit, and plasticity index of soils. American Society for Testing and Materials Test D4318-10e1. http://www.astm.org/Standards/D4318.htm. Accessed April 2016
  3. ASTM (2011) Standard practice for classification of soils for engineering purposes (Unified Soil Classification System). American Society for Testing and Materials Test D2487-11. http://www.astm.org/Standards/D2487.htm. Accessed April 2016

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© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Amec Foster WheelerLos AngelesUSA