IS 2720:1986 Part 11 is the Indian Standard (BIS) for methods of test for soils - determination of shear strength parameters of a soil by consolidated undrained triaxial compression test with pore water pressure measurement. This standard outlines the procedure for conducting a consolidated undrained (CU) triaxial compression test with pore water pressure measurement on soil. It determines the effective shear strength parameters (effective cohesion and effective angle of internal friction) necessary for advanced geotechnical stability analyses.
Describes the procedure for conducting consolidated undrained triaxial compression tests with pore water pressure measurement to determine soil shear strength parameters.
Overview
- Status
- Current
- Usage level
- Specialized
- Domain
- Geotechnical — Soil and Foundation
- Type
- Testing Method
Also on InfraLens for IS 2720
Practical Notes
! Ensure complete saturation of the specimen and de-airing of the pore pressure measuring lines before starting the test, typically verified by a B-value of 0.95 or higher.
! The rate of strain during shearing must be slow enough to allow equalization of pore water pressure throughout the specimen; this is critical in clayey soils.
! Filter paper drains can be used to accelerate the consolidation and saturation phases for highly impermeable soils.
Frequently referenced clauses
soilcohesive soilsandclay
International Equivalents
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Key Values4
Quick Reference Values
length to diameter ratio2 to 2.5
minimum specimen diameter38 mm
maximum particle sizeOne-sixth of the specimen diameter
acceptable B value for saturation>= 0.95
Key Formulas
sigma_1' = sigma_1 - u (Effective major principal stress)
sigma_3' = sigma_3 - u (Effective minor principal stress)
B = Delta u / Delta sigma_3 (Pore pressure parameter B)
A = Delta u / (Delta sigma_1 - Delta sigma_3) (Pore pressure parameter A)
Tables & Referenced Sections
Key Clauses
Clause 3 - Preparation of Test Specimens
Clause 4.2 - Saturation of Specimen
Clause 4.3 - Consolidation
Clause 4.4 - Shearing (Measurement of pore pressure)
Clause 5 - Calculations
Frequently Asked Questions3
What is the standard specimen size for the triaxial test?+
The minimum diameter is 38 mm, and the length-to-diameter ratio should be between 2.0 and 2.5.
How do you verify if the soil sample is fully saturated?+
By conducting a B-value check. A B-value (ratio of change in pore pressure to change in cell pressure) of 0.95 or greater generally indicates full saturation.
Why is the test performed at a very slow strain rate?+
To ensure uniform distribution and accurate measurement of pore water pressure within the specimen without inducing localized pressure gradients.
QA/QC Inspection Templates
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QA/QC templates coming soon for this code.