Which of the following statements is/are true for Unconfined Compression Test (UCT)? i. UCT is a special form of triaxial test in which the confining pressure is zero ii. UCT can be conducted only on sandy soils which can withstand without confinement
- AOnly (i)Correct
- BOnly (ii)
- CBoth (i) and (ii)
- DNeither (i) nor (ii)
Solution
Concept
Characteristics of unconfined compression test
Formula
NONE
Step-by-step solution
1. Unconfined compression testing is a simplified form of triaxial compression test where lateral confining pressure is equal to zero. 2. UCT is performed exclusively on intact, cohesive soils (clays) that can stand unconfined without collapsing, not on cohesionless sandy soils. 3. Therefore, statement i is true and statement ii is false. Answer: A
Explanation
The unconfined compression test is a special variation of a triaxial compression test where the lateral confining pressure is zero. This test requires cohesive soils that can stand unsupported, making it unsuited for cohesionless sandy soils that collapse without lateral support. Consequently, statement i is true and statement ii is false, making option A correct.
Why the other options are wrong
B) UCT cannot be conducted on sandy soils because cohesionless soils cannot stand unsupported without lateral confinement. C) Statement (ii) is false as UCT is performed on cohesive clay soils rather than sandy soils. D) Statement (i) is correct because UCT is indeed a triaxial test with zero confining pressure.
Shortcut
UCT is for cohesive clay soils (not sand) with zero confining pressure.
Common mistake
Selecting option C by assuming the test applies to sandy soils, ignoring that unconfined sand cannot stand without lateral pressure.
Correct answer: A) Only (i)