What type of sample is needed for consolidation testing of clay?

• A. Disturbed sample
• B. Undisturbed sample
• C. Granular sample
• D. Saturated sample

Answer: (B)

Consolidation testing is critical for understanding the compressibility and settlement behavior of clay soils. For this testing, an undisturbed sample is essential because it preserves the natural structure and water content of the soil. Clay is particularly sensitive to disturbances; when a sample is disturbed, it can alter the soil's properties significantly, such as its density, structure, and moisture content.

An undisturbed sample maintains the in-situ conditions, allowing for accurate measurement of the effective stress and the rate of consolidation when subjected to loading. The consolidation process relies on the ability to measure how much volume change occurs in response to an applied load, which can only be correctly observed with a sample that reflects the soil's natural state.

In contrast, disturbed samples do not accurately represent the in-situ condition and thus do not yield reliable results in consolidation tests. Granular samples may be more applicable to coarse materials rather than clay, and while saturation can affect the test results, it is the preservation of the soil structure through undisturbed sampling that is critical for accurate consolidation testing.