This standard prescribes the method to determine the shear strength parameters (cohesion and angle of shearing resistance) of soil using the triaxial compression test under unconsolidated undrained (UU) conditions. It is primarily used to evaluate the short-term stability of cohesive soils under rapid loading conditions.
Covers the determination of shear strength parameters of soil under undrained conditions using the triaxial compression test.
Quick Reference Values
Length to diameter (L/D) ratio2.0 to 2.5
Minimum specimen diameter38 mm
Maximum particle size1/5th to 1/6th of specimen diameter
Standard rate of strain (plastic failure)1 to 2 percent per minute
Key Formulas
Axial strain (ε) = ΔL / L0
Corrected Area (A) = A0 / (1 - ε)
Deviator Stress (σ1 - σ3) = Axial Load / Corrected Area (A)
Major Principal Stress (σ1) = Deviator Stress + Confining Pressure (σ3)
Practical Notes
Always check rubber membranes for pinhole leaks before conducting the test to prevent premature drainage or failure.
Undrained tests (UU) are fast and do not allow pore water dissipation, making them ideal for assessing short-term, end-of-construction stability in clays.
Ensure the specimen ends are perfectly flat and perpendicular to the axis to avoid eccentric loading and uneven stress distribution.