---
title: "Boring type for road sub-grade"
subject: "Foundation Engineering"
chapter: 2
key: "semester_5/foundation_engineering:boring-type-subgrade"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/boring-type-subgrade
site: BCT Engineering
---

# Boring type for road sub-grade

Foundation Engineering · Chapter 2: Soil Exploration

- Asked in: 2080 Bhadra, 2 marks
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/boring-type-subgrade
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-2

## Question

What type of boring is best suited for sub-grade investigation of roads and why?

## Short answer

Auger boring is best because road sub-grade investigation is shallow (1–3 m). It is cheap, fast, and light, allowing many closely spaced holes along the alignment. It provides disturbed but representative samples sufficient for classification, moisture content, Atterberg limits, compaction, and CBR tests.

## Answer

**Auger boring** (hand auger or small power auger) is the best method for road sub-grade investigation.
- Sub-grade soil is needed only to a shallow depth (about 1-3 m below formation level), where augers work well.
- It is cheap, fast and light, so many holes at close spacing (about 250-500 m or less) can be made along the alignment.
- It gives disturbed but representative samples that are enough for classification, moisture content, Atterberg limits, compaction (OMC, MDD) and CBR tests.
- It needs little equipment and is easily taken to hilly road sites.
Test pits can be used additionally for in-situ density and CBR checks.

## Check yourself

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

1. The best boring for road sub-grade investigation is
   A. rotary diamond drilling
   B. well sinking
   C. auger boring
   D. percussion with casing
   Answer: C. Depths are shallow and many holes are needed. (Key point: Best method)

2. Auger boring suits sub-grade because
   A. it gives undisturbed core
   B. it is cheap, fast and light, allowing many closely spaced holes
   C. it reaches 100 m
   D. it needs heavy rigs
   Answer: B. Roads need many shallow holes. (Key point: Why)

3. Auger samples are sufficient for
   A. triaxial tests on undisturbed soil
   B. consolidation tests
   C. classification, Atterberg limits, compaction and CBR tests
   D. pile load tests
   Answer: C. Disturbed representative samples are enough. (Key point: Tests)

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