---
title: "Why foundations; types of foundation"
subject: "Foundation Engineering"
chapter: 1
key: "semester_5/foundation_engineering:why-foundations-types"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/why-foundations-types
site: BCT Engineering
---

# Why foundations; types of foundation

Foundation Engineering · Chapter 1: Introduction

- Asked in: 2078 Bhadra, 2 marks
- Video: [Types of Foundation | Types of Footing | Types of Foundation in civil Engineering](https://www.youtube.com/watch?v=dO2lWAT-ltk) — Visual Civil
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/why-foundations-types
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-1

## Question

Why are foundations used? Describe different types of foundation.

## Short answer

Foundations spread structural loads to keep soil pressure below safe bearing capacity, limit settlement, provide stability below frost and scour, and resist uplift and lateral forces. Types: shallow (spread, strip, combined, raft) for near-surface good soil; deep (piles, piers, wells) for weak upper soils or heavy loads.

## Answer

#### Why foundations are used
- To spread the structural load over a large soil area so the pressure is less than the safe bearing capacity.
- To keep total and differential settlement within permissible limits.
- To place the structure on a stable level below frost, scour and weak surface soil.
- To resist uplift, overturning, sliding and lateral/seismic forces.

#### Types of foundation
**Shallow foundations** ($D_f \le B$)
- *Isolated (spread) footing:* one footing under each column; square, rectangular or circular.
- *Wall (strip) footing:* continuous footing under a load-bearing wall.
- *Combined footing:* common footing for two or more columns.
- *Strap footing:* two footings joined by a strap beam.
- *Raft (mat):* one large slab under the whole structure; used on weak soil or heavy loads.

**Deep foundations** ($D_f > B$)
- *Pile:* slender driven or bored member; end-bearing or friction pile.
- *Pier / drilled shaft:* large-diameter column, bored and concreted.
- *Well (caisson):* large hollow masonry or concrete cylinder sunk by dredging, used for bridge piers in rivers.

## Check yourself

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

1. A main reason for using a foundation is to
   A. concentrate the load on a small area
   B. increase the weight of the structure
   C. spread the load over a large soil area so pressure is less than safe bearing capacity
   D. prevent any settlement whatever
   Answer: C. Spreading reduces contact pressure below the safe bearing capacity. (Key point: Purpose)

2. A wall (strip) footing is
   A. one footing under each column
   B. a continuous footing under a load-bearing wall
   C. a footing joining two columns by a beam
   D. a hollow cylinder sunk by dredging
   Answer: B. Strip footings run along the wall length. (Key point: Wall footing)

3. Well (caisson) foundations are mainly used for
   A. small houses on rock
   B. light wall footings
   C. bridge piers in rivers
   D. roof supports
   Answer: C. Large hollow cylinders sunk by dredging suit river-bed bridge piers with scour. (Key point: Well foundation)

## Related in Foundation Engineering

- [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×
- [Classification of pile foundations](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-classification-material-load) — Foundation Engineering, chapter 8
- [Compensated foundation and types of mat](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Acompensated-foundation-mat-types) — Foundation Engineering, chapter 7, asked 7×
- [When well foundation is suitable](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Awell-suitability-advantages) — Foundation Engineering, chapter 9, asked 2×
- [When piles are preferred to shallow foundations](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-vs-shallow-conditions) — Foundation Engineering, chapter 8, asked 3×
- [Define and classify pile foundations](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-classification-define) — Foundation Engineering, chapter 8

## Related in other subjects

- [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
- [Foundations on black cotton soil](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ablack-cotton-foundation) — Building Technology, chapter 2
- [Common problems of existing foundations](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aproblems-existing-foundation) — Building Technology, chapter 2, asked 2×
- [When pile and mat foundations are chosen](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apile-mat-scenarios) — Building Technology, chapter 2