---
title: "Surface versus sub-surface investigation"
subject: "Engineering Geology II"
chapter: 4
key: "semester_4/engineering_geology_ii:surface-vs-subsurface-investigation"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/surface-vs-subsurface-investigation
site: BCT Engineering
---

# Surface versus sub-surface investigation

Engineering Geology II · Chapter 4: Engineering geology in site selection, investigation & construction/excavation

- Asked in: 2079 Chaitra, 2 marks
- Video: [Surface and Subsurface investigations](https://www.youtube.com/watch?v=kC7jQ4kvbyk) — Hemantkumar Bhosale
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/surface-vs-subsurface-investigation
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-4

## Question

Differentiate between surface and sub-surface site investigation methods.

## Short answer

Surface investigation studies ground exposures (mapping, air photos) to identify rock type, structure, and landslids; it is quick and cheap but limited to exposed features. Sub-surface investigation (test pits, boring, driling) provides depth, stratigraphy, and engineering properties directly, but is costly and point-wise.

## Answer

| Point | Surface investigation | Sub-surface investigation |
|---|---|---|
| Meaning | Study of surface exposures and ground features | Study of ground below the surface |
| Methods | Geological mapping, air-photo, remote sensing, outcrop study | Test pits, trenches, boring, drilling, adits; geophysics |
| Stage | Reconnaissance and preliminary | Preliminary to detailed |
| Information | Rock type, structure, landslides, geomorphology | Depth, thickness of strata, bed rock, water table, properties |
| Cost and time | Low, quick | High, slow |
| Accuracy | Limited, only exposed ground | Better for depth |
| Samples | Few | Disturbed and undisturbed samples |

## Check yourself

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

1. Which belongs to surface investigation?
   A. Test pits
   B. Geological mapping, air photo and remote sensing
   C. Boring
   D. Adits
   Answer: B. Test pits and drilling are sub-surface. (Key point: Methods)

2. Surface investigation compared to sub-surface is
   A. High cost and slow
   B. Always more accurate
   C. Low cost and quick
   D. Always gives undisturbed samples
   Answer: C. Sub-surface is costly and slow. (Key point: Cost and time)

3. Depth and thickness of strata come mostly from
   A. Surface mapping only
   B. Outcrop colour
   C. Topographic maps
   D. Sub-surface investigation
   Answer: D. Surface is limited to exposed ground. (Key point: Information)

## Close variants set in other exams

- [Direct methods of sub-surface investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Adirect-subsurface-methods) — Engineering Geology II, chapter 4, asked 3×

## Related in Engineering Geology II

- [Indirect sub-surface methods: tunnel and dam](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aindirect-subsurface-tunnel-dam) — Engineering Geology II, chapter 4
- [Indirect methods of surface investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aindirect-surface-methods) — Engineering Geology II, chapter 4
- [Purposes of site investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asite-investigation-purposes) — Engineering Geology II, chapter 4, asked 7×
- [Types and methods of site investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asite-investigation-methods) — Engineering Geology II, chapter 4, asked 7×
- [Detail stage of EG site investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Adetail-stage-investigation) — Engineering Geology II, chapter 4
- [Tunneling and site investigation process](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Atunneling-site-investigation-process) — Engineering Geology II, chapter 4

## Related in other subjects

- [Methods of surface and subsurface site investigation](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Amethods-of-surface-and-subsurface) — Engineering Geology I, chapter 1, asked 4×
- [Surface versus sub-surface drainage](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Asurface-vs-subsurface) — Transportation Engineering I, chapter 4, asked 2×
- [Contents of site investigation report](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asite-investigation-report) — Foundation Engineering, chapter 2, asked 5×
- [Engineering geological map and site investigation](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-geological-map-and-site) — Engineering Geology I, chapter 1, asked 3×