Engineering & geotechnics
Atterberg Limits & Plasticity
Liquid limit from the flow curve, class from the plasticity chart.
Fits the Casagrande flow curve to find the liquid limit at 25 blows, combines it with the plastic limit, and reports plasticity, liquidity, consistency and activity indices with the USCS fine-grained class on the plasticity chart.
Overview
Enter each cup trial as blows and water content. The tool fits water content against log blows, reads the liquid limit at 25 blows, and checks the one-point method. Plastic-limit trials are averaged.
What you enter · What you get
What you enter
- Cup trials: blows and water content
- Plastic-limit trials
- Natural water content and clay fraction (optional)
What you get
- Liquid limit, plastic limit, plasticity index
- Liquidity and consistency indices
- Flow and toughness indices, activity
- USCS class on the Casagrande chart
How it works in the field
Enter cup trials
Enter plastic-limit trials
Read the class
Method and equations
Plasticity chart
Casagrande’s A-line separates clays from silts; the U-line marks the upper bound of natural soils.
A: PI = 0.73 (LL − 20) · U: PI = 0.9 (LL − 8)
Indices
PI = LL − PL · LI = (w − PL)/PI · CI = (LL − w)/PI · A = PI / %clay
Who uses it
Soil-mechanics laboratoriesGeotechnical engineersStudents
Standards and references
- ASTM D4318-17. Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils.
- ASTM D2487-17. Standard Practice for Classification of Soils for Engineering Purposes (USCS).
- Casagrande, A. (1948). Classification and identification of soils. Transactions ASCE, 113, 901–930.
- Skempton, A.W. (1953). The colloidal activity of clays. Proc. 3rd ICSMFE, 1, 57–61.
Results support professional judgement. They do not replace a licensed engineer’s or geologist’s sign-off.
At a glance
- Category
- Engineering & geotechnics
- Runs on
- Phone, tablet and desktop browser
- Export
- PDF report, PNG charts, CSV
- Access
- Subscribers
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