What type of soil sample is typically used for grain-size analysis and specific gravity determination?

• A. A) Disturbed soil sample
• B. B) Undisturbed soil sample
• C. C) Mixed soil sample
• D. D) Composite soil sample

Answer: (A)

For grain-size analysis and specific gravity determination, a disturbed soil sample is typically preferred due to its practical collection and handling characteristics. Disturbed samples are collected from various depths or locations within a soil profile and can provide a more representative mixture of soil particles for laboratory analysis. This is essential because the goals are to examine the distribution of grain sizes and to determine properties such as specific gravity, which rely on the characteristics of the soil matrix as a whole.

In contrast to disturbed samples, undisturbed samples aim to preserve the original structure and natural moisture of the soil, which is crucial for certain tests but can complicate grain-size and specific gravity analysis, as their manipulation might alter the natural particle arrangement. Mixed and composite samples could also introduce variability that makes it difficult to correlate results to specific soil layers or conditions. Thus, disturbed samples strike a balance between representativeness and ease of analysis for the intended testing objectives.