---
title: "Road base void ratio specification"
subject: "Soil Mechanics"
chapter: 2
key: "semester_4/soil_mechanics:road-base-void-ratio-check"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/road-base-void-ratio-check
site: BCT Engineering
---

# Road base void ratio specification

Soil Mechanics · Chapter 2: Solids- Water –Air Relations and Index properties of soils

- Asked in: 2078 Poush, 4 marks
- Video: [Void ratio || Example solved](https://www.youtube.com/watch?v=N_yUQvgEdPU) — Civil Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/road-base-void-ratio-check
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-2

## Question

You are appointed as a supervisor for a road construction project. During the construction process, the contractor compacted the base course of the road and the average water content for the test samples was found to be 15%, the specific gravity of soil grains = 2.7 and unit weight of soil = 18 kN/m³. The specification requires that void ratio < 0.75. If you have to pass the bill for that task according to the specification, would you pass the bill for that work?

## Short answer

Dry unit weight is 15.65 kN/m³ giving void ratio 0.692, which is below the specified 0.75, so the bill should be passed.

## Answer

#### Given
$w = 15\%$, $G = 2.7$, $\gamma = 18$ kN/m³, specified $e < 0.75$. Take $\gamma_w = 9.81$ kN/m³.

#### Solution
Dry unit weight:
$$
\gamma_d = \frac{\gamma}{1+w} = \frac{18}{1.15} = 15.65\ \text{kN/m}^3
$$
Void ratio from $\gamma_d = \dfrac{G\gamma_w}{1+e}$:
$$
e = \frac{G\gamma_w}{\gamma_d} - 1 = \frac{2.7 \times 9.81}{15.65} - 1 = 0.692
$$

Since $e = 0.692 < 0.75$, the compaction **meets the specification**.

**Decision: pass the bill** for this base course work. (A check using the average of several samples is taken as given; individual samples should also be checked.)

## Check yourself

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

1. Dry unit weight is:
   A. 18 kN/m3
   B. 20.7 kN/m3
   C. 15.65 kN/m3
   D. 12.2 kN/m3
   Answer: C. 18/1.15 = 15.65. (Key point: Dry unit weight)

2. Void ratio is found from:
   A. e = G gamma_w/gamma_d - 1
   B. e = G gamma_w/gamma - 1
   C. e = wG
   D. e = gamma_d/G
   Answer: A. Use dry unit weight: gamma_d = G gamma_w/(1+e). (Key point: Formula)

3. The void ratio is about:
   A. 0.75
   B. 0.85
   C. 0.69
   D. 0.45
   Answer: C. 2.7 x 9.81/15.65 - 1 = 0.692. (Key point: Value)

4. Should the bill be passed?
   A. Yes, e = 0.692 < 0.75 meets the specification
   B. No, e is too high
   C. No, w is too high
   D. Cannot decide without G
   Answer: A. The requirement is e < 0.75, which is satisfied. (Key point: Decision)

## Related in Soil Mechanics

- [Pycnometer data, water content, γsub](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Apycnometer-water-content-submerged) — Soil Mechanics, chapter 2
- [Compacted soil 17 kN/m³, OWC 16%](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Amax-dry-weight-17-void-ratio) — Soil Mechanics, chapter 5, asked 2×
- [Compacted soil 18 kN/m³, porosity and ZAV](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Amax-dry-weight-18-porosity-zav) — Soil Mechanics, chapter 5, asked 2×
- [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
- [Compacted soil 18 kN/m³, saturation](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Amax-dry-weight-18-saturation) — Soil Mechanics, chapter 5
- [Phase diagram; void ratio, saturation](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Aphase-diagram-void-ratio-saturation) — Soil Mechanics, chapter 2

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