Plasticity Index

UKAS Accredited

Standard(s): BS EN ISO 17892-12:2018+A2:2022
Lab Test
The Plasticity Index (PI) test determines the range of moisture content over which a soil behaves plastically. It is calculated as the difference between the Liquid Limit and the Plastic Limit of the soil. In accordance with BS EN ISO 17892-12:2018+A2:2022, the Plasticity Index provides an indication of soil behaviour, particularly its compressibility, workability, and potential for volume change.

Enquire about this test

The Process

A representative soil sample is prepared and tested to determine its Liquid Limit and Plastic Limit. The Liquid Limit identifies the moisture content at which the soil begins to behave like a liquid, while the Plastic Limit identifies the point at which the soil transitions from a plastic to a semi-solid state. The Plasticity Index is then calculated by subtracting the Plastic Limit from the Liquid Limit.

The Reason

The Plasticity Index helps engineers understand how soils will behave when exposed to varying moisture conditions. Soils with a high PI tend to be more compressible and may be prone to shrink–swell behaviour or settlement. Determining the Plasticity Index is therefore important when assessing soil suitability for construction.

The Application

Plasticity Index testing is widely used in geotechnical investigations and earthworks projects. It helps classify soils and assess their suitability for use in embankments, subgrades, and fill materials. The results also assist engineers in predicting ground movement, settlement risks, and the need for soil improvement or stabilisation.

Frequently Asked Questions

Can Amtest carry out Plasticity Index testing for my project?

Yes. Amtest can perform Plasticity Index testing in accordance with BS EN ISO 17892-12:2018+A2:2022 as part of geotechnical investigations and earthworks testing.

Why is Plasticity Index testing important before construction?

The Plasticity Index helps identify soils that may compress, shrink, or expand with changes in moisture. Amtest testing provides valuable information for engineers designing foundations, pavements, and earthworks.

What types of soil can be tested for Plasticity Index?

Plasticity Index testing is typically carried out on fine-grained soils such as clays and silts. Amtest can assess a wide range of soil samples collected from site investigations or earthworks.

Will Amtest provide results suitable for engineering design?

Yes. Amtest provides clear laboratory reports detailing the Liquid Limit, Plastic Limit, and calculated Plasticity Index to support engineering assessment and compliance with project specifications.

View more Aggregates testing services:

View all

Plastic Limit

Determination of the plastic limit of fine-grained soils in accordance with BS EN ISO 17892-12:2018+A2:2022.
BS EN ISO 17892-12:2018+A2:2022
Aggregates
UKAS Accredited
Lab Test
View Test

Particle Size Distribution

Determination of particle size distribution of aggregates using sieving in accordance with BS EN 933-1:2012.
BS EN 933-1:2012
Aggregates
UKAS Accredited
Lab Test
View Test

Sample Reduction

Sample reduction by riffle box, by quartering, or to a test portion of a specified mass within a small tolerance
BS EN 932-2:1999
Aggregates
UKAS Accredited
Lab Test
View Test

Dynamic Cone Penetration (TRL-DCP)

Rapid measurement of the in-situ strength of existing flexible pavements constructed with unbound materials.
DMRB, CS 229 Data for Pavement Assessment Rev.0: 2020
Aggregates
UKAS Accredited
Lab Test
Site Test
View Test

In-Situ California Bearing Ratio (CBR)

Penetration of soil with a plunger over a standard area. The harder the surface, the higher the CBR percentage.
Aggregates
Site Test
View Test

Constituents of Course Recycled Aggregates

Ensure the quality and compliance of recycled aggregates with our constituents analysis, supporting sustainable and reliable construction practices.
BS EN 933-11:2009
Aggregates
UKAS Accredited
Site Test
View Test

Plasticity Index

A higher Plasticity Index indicates a greater range of water content where soil remains plastic, signifying higher compressibility and potential for settlement.
BS EN ISO 17892-12:2018+A2:2022
Aggregates
UKAS Accredited
Lab Test
View Test

Water Content

Determination of the water content of aggregates in accordance with BS EN 1097-5:2008.
BS 1377-2:2022
Aggregates
UKAS Accredited
Lab Test
View Test

In-Situ Bulk Density Nuclear Method

The in-situ bulk density nuclear method ensures soil compaction meets construction standards by measuring density and moisture directly on-site.
BS 1377-9:1990
Aggregates
Site Test
View Test

Resistance to Fragmentation – Los Angeles Test

Subjects a coarse aggregate sample to abrasion, impact, and grinding.
BS EN 1097-2:2020
Aggregates
UKAS Accredited
Lab Test
View Test
Lab Test
Plasticity Index

The Plasticity Index (PI) measures the range of water content over which soil remains plastic, providing valuable insight into the clay content and compressibility of the material.

The Process

  1. Sample Preparation: A soil sample is dried and sieved to remove larger particles, isolating the fine-grained fraction.
  2. Liquid Limit Determination: The water content at which the soil changes from a plastic to a liquid state is measured.
  3. Plastic Limit Determination: The water content at which the soil transitions from a plastic to a solid state is measured.
  4. Calculation of PI: The PI is calculated as the difference between the liquid limit and the plastic limit: PI = Liquid Limit - Plastic Limit

Why Is This Test Important?

  • Soil Classification: Identifies soil types and their suitability for construction.
  • Compressibility Indicator: Predicts how the soil will behave under load, including settlement risks.
  • Workability: Assesses how easily the soil can be manipulated during construction.
  • Stability Assessment: Determines the soil's resilience to water-induced volume changes.

The Plasticity Index test is crucial for soil analysis in infrastructure projects, ensuring safe and effective construction. Contact us for accurate PI testing and expert guidance.

BS EN ISO 17892-12:2018+A2:2022