The unconfined compressive strength test is a/an:

Asked in SSC JE 2009

Detailed Explanation

In the unconfined compression test, a clay cylinder is compressed axially to failure within a few minutes, with no confining pressure and no drainage arrangement.

Why “Undrained test” Is Correct

Because the clay has no time to drain, the water content stays constant: it is an undrained test. It is in fact a special case of the UU triaxial test with zero cell pressure.

Unconfined compression apparatus (schematic). A cylindrical clay specimen sits between conical seatings and is compressed by turning the handle. The proving ring measures the load and a dial gauge measures the shortening. No lateral (cell) pressure is applied, so σ₃ = 0 and q_u = 2c for a φ = 0 clay.

Why the Other Options Are Wrong

B. Drained test: No drainage occurs during the short test.
C. Consolidated undrained test: There is no consolidation stage at all.
D. None of the above: It is an undrained test.

Key Point

UCS = UU with σ₃ = 0 → qu = 2cu.

Key Concepts for Students

Strain rate typically 0.5–2% per minute.
Used for saturated, intact clays.
Sensitivity is found by repeating on a remoulded specimen.

Practice more: this is question 46 in Shear Strength of Soils MCQs – Part 4. Try the whole set and check every answer instantly.