The 'sample disturbance' in soil sampling is measured by 'area ratio' Ar defined as:
Choose the correct answer
Ratio of sample length to tube length
(De²−Di²)/Di² × 100% — area ratio < 10–15% required for undisturbed (high quality) sampling
Ratio of sample mass to tube mass
Ratio of water content to plastic limit
Correct Answer
B. (De²−Di²)/Di² × 100% — area ratio < 10–15% required for undisturbed (high quality) sampling
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Area ratio Ar = (De²−Di²)/Di² × 100% where De = external diameter, Di = internal (cutting tip) diameter of sampler. For undisturbed samples: Ar < 10–15% (IS 2132). High Ar → soil displaced → disturbed sample → inaccurate lab results. Thin-wall Shelby tube: Ar ≈ 10%. Standard split-spoon (SPT): Ar ≈ 112% (very disturbed — not for testing, only classification).
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