---
title: "Maintaining OMC in the field"
subject: "Soil Mechanics"
chapter: 5
key: "semester_4/soil_mechanics:optimum-moisture-maintain-field"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/optimum-moisture-maintain-field
site: BCT Engineering
---

# Maintaining OMC in the field

Soil Mechanics · Chapter 5: Soil Compaction

- Asked in: 2078 Poush, 1 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/optimum-moisture-maintain-field
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-5

## Question

Is it practically possible to maintain the optimum moisture content during compaction at field? Give reason.

## Short answer

It is not fully possible to maintain exact OMC in the field, but can be kept within ±2%. Reasons: evaporation, rain, non-uniform borrow soil, differences between lab and field compaction energy, and lag in moisture testing.

## Answer

It is **not fully possible** to maintain the exact optimum moisture content in the field, but it can be kept within about $\pm 2\%$ of the OMC.

Reasons:
- Water content changes after sprinkling, because of evaporation by sun and wind or addition by rain during hauling, spreading and rolling.
- The borrow soil is non-uniform, so moisture is variable and cannot be mixed perfectly.
- The field OMC differs from the laboratory OMC, since the field compaction energy and method are different.
- Water content is checked only in selected spots, and the test results take time.

## Check yourself

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

1. Maintaining exact OMC in the field is:
   A. Never needed
   B. Not fully possible, but within about +/-2%
   C. Possible with no testing
   D. Fully possible
   Answer: B. Variation is unavoidable; +/-2% is practical. (Key point: Possibility)

2. A reason water content varies is:
   A. Perfect mixing
   B. Uniform borrow soil
   C. Evaporation by sun and wind or rain during hauling and rolling
   D. Constant temperature
   Answer: C. Water content changes after sprinkling. (Key point: Reason)

3. Field OMC differs from lab OMC because:
   A. Field energy and method differ
   B. Soil is different mineral
   C. Particle sizes are zero
   D. Lab uses no water
   Answer: A. Compaction effort changes OMC. (Key point: Lab vs field OMC)

## Related in Soil Mechanics

- [Compaction test: curve, MDD, OMC, RC](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Acompaction-test-curve-mdd-omc-rc) — Soil Mechanics, chapter 5, asked 2×
- [ZAV; field compaction precautions](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Azero-air-void-field-precautions) — Soil Mechanics, chapter 5
- [Road compaction specification, sand cone](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aroad-compaction-sand-cone-check) — Soil Mechanics, chapter 5
- [Compaction test, RC and saturation](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Acompaction-test-curve-saturation-degree) — Soil Mechanics, chapter 5, asked 2×
- [Field compaction methods; Proctor curves](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Afield-compaction-methods-proctor-curves) — Soil Mechanics, chapter 5
- [Draw compaction curve with features](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Acompaction-curve-features) — Soil Mechanics, chapter 5

## Related in other subjects

- [Optimum binder content graphs](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Aoptimum-binder-content) — Transportation Engineering I, chapter 6
- [Define moisture content, superheated vapor, etc.](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Amoisture-superheated-definitions) — Fundamental of Thermodynamics & Heat Transfer, chapter 3
- [Quality, moisture content, specific volume of mixture](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Aquality-moisture-specific-volume) — Fundamental of Thermodynamics & Heat Transfer, chapter 3
- [Field capacity, available moisture definitions](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Adefine-fc-am-ram-deficiency) — Irrigation and Drainage Engineering, chapter 2