Area ratio of sampler, radius 30 mm

Short answer

Inside diameter D1=60−2×2.25=55.5 mm, Ar=(60²−55.5²)/55.5²×100=16.87%. Not recommended for undisturbed sampling because Ar >> 10%, causing excessive soil displacement.

Determine the area ratio of a sampler having an external radius of 30 mm and a wall thickness of 2.25 mm. Do you recommend this sampler for obtaining undisturbed soil samples and why?

External radius 30 mm gives outside diameter $D_3 = 60$ mm. Wall thickness 2.25 mm gives inside diameter

D_1 = 60 - 2\times2.25 = 55.5\ \text{mm}

A_r = \frac{D_3^2-D_1^2}{D_1^2}\times100 = \frac{60^2-55.5^2}{55.5^2}\times100 = \frac{519.75}{3080.25}\times100 = 16.87\%

Answer: $A_r = 16.87\%$ .

Recommendation: not recommended for undisturbed sampling. The area ratio is more than 10% (limit 10%, or 20% at most for stiff soil), so the thick wall displaces too much soil and disturbs the sample. It is fit only for disturbed or stiff-soil sampling.

✓ Answer checked by Claude Sonnet 5.5

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