Soil Exploration MCQ with answer and solution

Concept

The Standard Penetration Test (SPT) yields disturbed soil samples, not undisturbed ones, making option A the incorrect statement.

Step-by-step solution

1. Understand the purpose and procedure of the Standard Penetration Test (SPT). 2. Note that SPT uses a split-spoon sampler driven by hammer blows, which severely disturbs the natural structure of the soil. 3. Conclude that the samples retrieved from SPT are disturbed and cannot be used for laboratory tests requiring undisturbed samples (such as triaxial or consolidation tests), though they can be used for general soil classification. 4. Verify that options B, C, and D are standard correct facts about SPT.

Explanation

In the Standard Penetration Test (SPT), the split-spoon sampler is driven into the soil, which inherently causes significant disturbance to the soil structure. Therefore, good quality undisturbed soil samples cannot be obtained from SPT; only disturbed samples are recovered (which are nevertheless suitable for soil classification).

Why the other options are wrong

B: SPT is economical and less time-consuming/expensive compared to a full-scale plate load test. C: Samples obtained from the split-spoon are widely used for index property tests and soil classification. D: SPT N-values are heavily relied upon for empirical correlations in shallow and deep foundation design in cohesionless (sandy) soils.

Shortcut

Remember: SPT gives disturbed samples. For undisturbed samples in cohesive soils, thin-walled samplers (Shelby tubes) are used.

Common mistake

Confusing disturbed samples obtained from SPT split-spoon samplers with undisturbed samples required for shear strength or consolidation testing.