---
title: "Sampler disturbed or undisturbed check"
subject: "Foundation Engineering"
chapter: 2
key: "semester_5/foundation_engineering:sampler-40-42-mm"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/sampler-40-42-mm
site: BCT Engineering
---

# Sampler disturbed or undisturbed check

Foundation Engineering · Chapter 2: Soil Exploration

- Asked in: 2078 Bhadra, 2 marks
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/sampler-40-42-mm
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-2

## Question

The internal diameter of a sampler is 40 mm and the external diameter is 42 mm. Will you consider the sample obtained from the sampler as disturbed or undisturbed?

## Short answer

Area ratio Ar=(42²−40²)/40²×100 = 10.25%. Since Ar slightly exceeds the 10% limit for undisturbed samples, the sample is disturbed.

## Answer

Take the 40 mm as the inside diameter $D_1$ and the 42 mm as the outside diameter $D_3$ of the cutting edge (wall 1 mm thick).

$$
A_r = \frac{D_3^2-D_1^2}{D_1^2}\times100 = \frac{42^2-40^2}{40^2}\times100 = \frac{164}{1600}\times100 = 10.25\%
$$

The limit for an undisturbed sample is $A_r \le 10\%$. Since $A_r = 10.25\% $ is slightly greater than 10%, the sample is classed as **disturbed** (marginal; it may be accepted as nearly undisturbed in soft or stiff clay if the clearances are right, but by the criterion it is not).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. For D1 = 40 mm and D3 = 42 mm, the area ratio is
   A. 5%
   B. 2.5%
   C. 10.25%
   D. 20.5%
   Answer: C. (42^2 - 40^2)/40^2 = 164/1600. (Key point: Calculation)

2. The criterion for an undisturbed sample is
   A. Ar <= 10%
   B. Ar >= 10%
   C. Ar <= 50%
   D. Ar = 0%
   Answer: A. Area ratio should be at most 10%. (Key point: Criterion)

3. The sample is
   A. disturbed, marginally, since 10.25% > 10%
   B. undisturbed, since close to 10%
   C. undisturbed always
   D. cannot be determined at all
   Answer: A. By the criterion it is not undisturbed. (Key point: Conclusion)

## Related in Foundation Engineering

- [Sampler clearances and area ratio (68 mm)](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asampler-clearance-68-70) — Foundation Engineering, chapter 2
- [Disturbed vs undisturbed samples](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Adisturbed-vs-undisturbed-sample) — Foundation Engineering, chapter 2, asked 2×
- [Area ratio of sampler, radius 30 mm](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asampler-area-ratio-radius) — Foundation Engineering, chapter 2
- [Sampler clearances and area ratio (59 mm)](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asampler-clearance-59-63) — Foundation Engineering, chapter 2, asked 2×
- [Sampler clearances and area ratio (69 mm)](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asampler-clearance-69-73) — Foundation Engineering, chapter 2, asked 2×
- [Sampler design parameters and significance](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asampler-design-parameters) — Foundation Engineering, chapter 2, asked 6×

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