Soil Exploration MCQ with answer and solution

Concept

Area ratio of a sampler determines the soil disturbance; lower area ratio means less displacement and less disturbance to the soil sample.

Formula

Area Ratio = ((D₂² - D₁²) / D₁²) × 100

Step-by-step solution

1. Understand the definition of Area Ratio in soil sampling: Ar = [(D₂² - D₁²) / D₁²] × 100, where D₂ is outer diameter and D₁ is inner diameter. 2. For an undisturbed sample, the displacement of soil should be minimal. 3. Standard specification states that the area ratio should be ≤ 10% for a soil sample to be considered undisturbed.

Explanation

The area ratio is a criterion used to evaluate the degree of disturbance caused by a sampling tube during soil exploration. For a soil sample to be considered undisturbed, the area ratio should be less than or equal to 10% for soft to firm clays, though up to 20% may be acceptable for stiff soils.

Why the other options are wrong

B: '> 10%' represents significant disturbance. C: '> 25%' is extremely high and causes severe disturbance. D: '≤ 25%' is too high to qualify as a generally undisturbed sample criteria in standard specifications.

Shortcut

Remember: 'Undisturbed = ≤ 10% area ratio'.

Common mistake

Confusing area ratio with cutting edge angle or inside clearance.