Which of the following parameters is determined by the triaxial test?

Asked in SSC JE 25/01/2018 (Evening)

Detailed Explanation

The triaxial compression test is run on several identical specimens at different cell pressures. Each gives a Mohr circle at failure, and the envelope touching them gives the shear strength parameters.

Why “Shear strength parameters” Is Correct

The output of the test is c and φ (or c′ and φ′, or c_u) — the shear strength parameters. That is its purpose.

Stresses on a triaxial specimen. The cell (confining) pressure σ₃ acts all round; the ram adds the deviator stress σ_d on top. So σ₁ = σ₃ + σ_d is vertical, and the two horizontal principal stresses are both equal to σ₃ (σ₂ = σ₃).

Why the Other Options Are Wrong

A. Hydraulic gradient: Hydraulic gradient is a seepage quantity (head loss per length).
B. Permeability: Permeability is found with constant-head or falling-head permeameters (a triaxial cell can be adapted, but that is not its standard use).
D. Grain size: Grain size comes from sieve and hydrometer analysis.

Key Point

Triaxial test → c, φ (plus pore-pressure parameters and stiffness).

Key Concepts for Students

At least three specimens are tested.
CU tests with pore-pressure measurement give both total and effective parameters.
Stress–strain curves also give modulus of elasticity.

Practice more: this is question 32 in Shear Strength of Soils MCQs – Part 3. Try the whole set and check every answer instantly.