---
title: "Investigation details for bridge foundation"
subject: "Foundation Engineering"
chapter: 2
key: "semester_5/foundation_engineering:bridge-foundation-investigation"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/bridge-foundation-investigation
site: BCT Engineering
---

# Investigation details for bridge foundation

Foundation Engineering · Chapter 2: Soil Exploration

- Asked in: 2078 Kartik, 5 marks
- Video: [Geotechnical Investigation – It’s Significance & Relevance: Case Study of a Bridge Site| Engineering](https://www.youtube.com/watch?v=1VwMzdRvoV8) — Geotechnical Engineering Consultancy
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/bridge-foundation-investigation
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-2

## Question

For a site investigation for the design of a bridge foundation, what kind of detailed information do you set out to obtain?

## Short answer

Obtain subsoil profile at each pier and abutment from boreholes, engineering properties (strength, SPT N, rock RQD), groundwater level and chemistry, river data (flood level, scour depth), pile/well capacity parameters, seismic/liquefaction potential, and construction aspects. Bore depth ≥1.5× foundation width below foundation level, at least 3 m into rock.

## Answer

For a bridge foundation the investigation must give the information needed for the pier, abutment and approach design. It seeks:
1. **Subsoil profile at every pier and abutment:** boreholes at each foundation location, with soil type, thickness, density/consistency, and depth to rock or hard stratum.
2. **Engineering properties:** unit weight, $c$, $\phi$, SPT $N$, compressibility and bearing capacity (and rock RQD, strength, core recovery for rock).
3. **Groundwater data:** level, fluctuation, artesian pressure and chemical content (sulphates, chlorides) for durability.
4. **River data:** high flood level, low water level, discharge and velocity, bed material and the **scour depth** (decides foundation level); type of bank, river training and possible shifting.
5. **Deep foundation parameters:** pile or well capacity, skin friction, end bearing, negative skin friction, and presence of boulders and obstructions that could stop the sinking of wells/piles.
6. **Seismic and geology:** faults, liquefiable sand layers, seismic zone, slope stability of abutments and approach embankments.
7. **Construction aspects:** cofferdam or caisson needs, dewatering, access, availability of local materials, and effects on adjacent structures.
The depth of boring is at least 1.5 times the width of the foundation below the foundation level (and 3 m or more into rock).

## Check yourself

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

1. For a bridge, boreholes are located
   A. only at one end
   B. only at the middle
   C. at every pier and abutment
   D. away from the river
   Answer: C. Subsoil profile is needed at each foundation. (Key point: Borehole locations)

2. Scour depth is important because it
   A. determines only the deck width
   B. decides the foundation level
   C. has no effect on foundations
   D. only affects the approach road
   Answer: B. Foundations must be below scour. (Key point: Scour)

3. Why check sulphates and chlorides in groundwater?
   A. For taste of water
   B. To decide the pier colour
   C. For the durability of the foundation
   D. To reduce load
   Answer: C. Aggressive chemicals attack concrete. (Key point: Chemical)

## Related in Foundation Engineering

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