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.
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)
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.