---
title: "Disturbed vs undisturbed samples"
subject: "Foundation Engineering"
chapter: 2
key: "semester_5/foundation_engineering:disturbed-vs-undisturbed-sample"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/disturbed-vs-undisturbed-sample
site: BCT Engineering
---

# Disturbed vs undisturbed samples

Foundation Engineering · Chapter 2: Soil Exploration

- Asked in: 2080 Baisakh, 2+2 marks; 2078 Bhadra, 2+1 marks (asked 2 times)
- Video: [Disturbed and Undisturbed Samples | Madhukant Goyal (IES) | #AlphaConcepts](https://www.youtube.com/watch?v=LkJM2d2RLr8) — Alpha Learning
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/disturbed-vs-undisturbed-sample
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-2

## Question

Differentiate between disturbed and undisturbed soil samples. What are the factors affecting the quality (disturbance) of a sample?

## Short answer

Disturbed samples lose natural structure, are obtained with augers or split spoons, and suit classification tests. Undisturbed samples retain structure and moisture, are taken with thin-walled samplers, and allow strength and consolidation tests. Quality depends on sampler design, insertion method, soil sensitivity, stress relief, and handling.

## Answer

| Point | Disturbed sample | Undisturbed sample |
|---|---|---|
| Structure | Natural structure and density destroyed | Natural structure, density and moisture largely retained |
| Representative? | Yes, constituents are present (mixed) | Yes, in structure and content |
| Collection | Auger, split spoon, test pit by hand | Thin-walled Shelby tube, piston sampler, block sampling |
| Tests possible | Grain size, specific gravity, Atterberg limits, compaction | Shear strength, consolidation, permeability, unit weight |
| Cost | Cheap, easy | Costly and needs care |
| Use | Classification and identification | Design parameters |

#### Factors affecting the quality of a sample
- **Sampler design:** area ratio, inside and outside clearances, cutting edge sharpness.
- **Method of boring and advancing** (water jets, disturbed bottom of hole, bottom heave).
- **Method of sampling:** pushing vs hammering, speed and rate of insertion.
- **Type of soil:** soft sensitive clays and loose sands are easily disturbed.
- **Stress release** when the sample is taken out, and possible swelling.
- **Handling, transport and storage:** vibration, moisture loss, rough handling, time delay, extrusion method.

## Check yourself

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

1. Which tests need an undisturbed sample?
   A. Grain size and Atterberg limits
   B. Shear strength, consolidation and permeability
   C. Specific gravity only
   D. Compaction tests
   Answer: B. These properties depend on natural structure and density. (Key point: Undisturbed tests)

2. Undisturbed samples are typically collected by
   A. auger cuttings
   B. thin-walled Shelby tube, piston sampler or block sampling
   C. split spoon blows
   D. hand mixing in test pit
   Answer: B. Thin-walled tubes and block sampling preserve structure. (Key point: Collection)

3. Which soils are easily disturbed during sampling?
   A. Hard rock
   B. Dense gravel
   C. Soft sensitive clays and loose sands
   D. Dry stiff boulders
   Answer: C. Soft sensitive clays and loose sands lose structure with little disturbance. (Key point: Disturbance factors)

4. Which factor affects sample quality?
   A. The colour of the tube paint
   B. The name of the project
   C. The day of the week
   D. Sampler design, such as area ratio and clearances
   Answer: D. Sampler geometry, boring method, handling and storage all affect disturbance. (Key point: Quality factors)

## Related in Foundation Engineering

- [Sampler disturbed or undisturbed check](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asampler-40-42-mm) — Foundation Engineering, chapter 2
- [Why undisturbed samples are required](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Awhy-undisturbed-samples) — Foundation Engineering, chapter 2
- [Factors affecting bearing capacity; water table](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Abearing-capacity-factors-water-table) — Foundation Engineering, chapter 6, asked 5×
- [Representative vs non-representative samples](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Arepresentative-samples) — Foundation Engineering, chapter 2
- [Factors affecting selection of pile type](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-type-selection-factors) — Foundation Engineering, chapter 8

## Related in other subjects

- [Soil moisture forms; factors affecting CWR](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Asoil-moisture-forms-cwr-factors) — Irrigation and Drainage Engineering, chapter 2
- [Cost vs value; factors affecting valuation](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Acost-vs-value-factors) — Construction Management, chapter 13
- [Quality; QA vs QC; factors in Nepal](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aquality-qa-qc-nepal-factors) — Project Engineering, chapter 4
- [Differentiate quality control and assurance](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aqa-vs-qc-differentiate) — Project Engineering, chapter 4