---
title: "Functions of foundation, deep foundation types"
subject: "Building Technology"
chapter: 2
key: "semester_6/building_technology:foundation-functions-deep"
source: https://www.bctengineer.com/q/semester_6/building_technology/foundation-functions-deep
site: BCT Engineering
---

# Functions of foundation, deep foundation types

Building Technology · Chapter 2: Foundations

- Asked in: 2071 Bhadra, 8 marks
- Video: [Pile Foundation and It's Types | Bridge Engineering | Lec - 05](https://www.youtube.com/watch?v=6mAaqD7BdmI) — STRUCTURE-TECH
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/foundation-functions-deep
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-2

## Question

What are the functions of foundation? Explain the types of deep foundation with necessary sketches.

## Short answer

Foundation functions include transferring load within bearing capacity, spreading load, controlling settlement, providing a firm level base, resisting lateral loads and uplift, and protecting from moisture and frost. Deep foundation types are pile, pier, well or caisson, under-reamed piles, and drilled shafts.

## Answer

#### Functions of foundation
1. Transfers the building load safely to the soil, within the bearing capacity.
2. Spreads the load over a large area to reduce the pressure.
3. Keeps settlement uniform and within limits.
4. Gives a firm, level base for the structure.
5. Resists lateral loads, sliding and overturning (wind, earthquake, earth pressure).
6. Gives stability against uplift (tall structures) and soil movement, such as shrinkage or swelling.
7. Protects the building from the effects of ground moisture, frost and chemicals.

#### Types of deep foundation
1. **Pile foundation**: Long slender members driven or bored into the ground.
   - *End-bearing piles* transmit load to a hard stratum.
   - *Friction piles* transfer load by skin friction.
   - By material: timber, RCC (precast or cast-in-situ), steel; by installation: driven or bored.
   - A pile cap joins the pile group under a column.
2. **Pier foundation**: Large diameter vertical cylinder or column of masonry or concrete, used for heavy loads on firm strata at moderate depth.
3. **Well (caisson) foundation**: A hollow cylinder or box (brick, concrete) sunk through soil by dredging inside, then plugged with concrete; used for bridge piers under water.
4. **Under-reamed piles**: Piles with bulbs at the lower end, for expansive soil.
5. **Drilled shafts (bored piles)**: Large concrete shaft drilled in the ground.

```text
 pile cap [=======]      pier    well
   | | |                 | |     |  |
   | | |                 | |     |__|
 =hard layer=         =hard=   sunk
```

## Check yourself

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

1. A primary function of a foundation is to:
   A. Spread load over a large area to reduce soil pressure
   B. Provide decoration
   C. Increase building weight
   D. Raise the water table
   Answer: A. Spreading load reduces pressure within bearing capacity. (Key point: Function of foundation)

2. Friction piles carry load mainly by:
   A. Suction
   B. Tension in the cap
   C. Bearing on hard stratum
   D. Skin friction along the shaft
   Answer: D. End-bearing piles use a hard stratum; friction piles use skin friction. (Key point: End-bearing vs friction)

3. A well (caisson) foundation is sunk by:
   A. Driving with hammers
   B. Dredging inside and then plugging with concrete
   C. Blasting
   D. Jacking only
   Answer: B. Material inside is dredged so the well sinks, then it is plugged with concrete; used for bridge piers. (Key point: Well foundation)

4. Under-reamed piles are used in:
   A. Dry sand only
   B. Frozen ground only
   C. Expansive soil
   D. Solid rock
   Answer: C. The bulbs resist uplift in expansive soil. (Key point: Under-reamed piles)

## Related in Building Technology

- [Deep foundation types and use of shallow foundations](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Adeep-shallow-types-079a) — Building Technology, chapter 2
- [Why joints are necessary; expansion joint](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ajoints-why-expansion) — Building Technology, chapter 10, asked 2×
- [Foundation requirements and shallow foundation types](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Afoundation-define-requirements-shallow) — Building Technology, chapter 2
- [Foundation and its types](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Afoundation-types-sketches) — Building Technology, chapter 2
- [Foundation settlement causes and underpinning](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Asettlement-underpinning-067as) — Building Technology, chapter 2
- [Types of shallow foundation](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ashallow-foundation-types) — Building Technology, chapter 2

## Related in other subjects

- [Shallow versus deep foundation](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Ashallow-vs-deep-foundation) — Foundation Engineering, chapter 1
- [Shallow and deep wells](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ashallow-deep-wells) — Water Supply Engineering, chapter 2, asked 4×
- [Classify shallow and deep foundations](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aclassify-foundations-soil) — Foundation Engineering, chapter 1, asked 4×
- [Well foundation: excavation, sinking, brick, PCC curb](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Awell-foundation-d-four-items) — Estimating and Costing, chapter 6, asked 2×