This standard specifies the laboratory method for determining the shear strength parameters of soils (cohesion and angle of internal friction) using a direct shear apparatus. It provides step-by-step procedures for unconsolidated-undrained, consolidated-undrained, and consolidated-drained tests.
Specifies the method for conducting direct shear tests on soil samples to determine shear strength parameters (cohesion and angle of internal friction).
Quick Reference Values
typical small shear box size60 mm x 60 mm
typical minimum specimen thickness20 mm
minimum thickness to maximum particle size ratio6
maximum particle size for 60mm box4.75 mm
Key Formulas
Shear Stress (τ) = Applied Shear Force / Area of cross-section
Normal Stress (σ) = Applied Normal Load / Area of cross-section
τ = c + σ * tan(φ) — Mohr-Coulomb failure criterion
Practical Notes
Direct shear test forces the failure plane to be predetermined and horizontal, which may not always be the weakest plane of the soil specimen.
Pore water pressures cannot be measured during this standard test, making effective stress parameters difficult to reliably obtain for saturated clays.
Ensure the gap between the upper and lower halves of the shear box is slightly larger than the maximum particle size to prevent friction between the metal box halves during shearing.