---
title: "When piles are preferred to shallow foundations"
subject: "Foundation Engineering"
chapter: 8
key: "semester_5/foundation_engineering:pile-vs-shallow-conditions"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/pile-vs-shallow-conditions
site: BCT Engineering
---

# When piles are preferred to shallow foundations

Foundation Engineering · Chapter 8: Pile Foundations

- Asked in: 2078 Kartik, 2 marks; 2076 Asoj, 1 marks; 2074 Asoj, 3 marks (asked 3 times)
- Video: [when do we prefer pile foundation? Types and Installation procedure](https://www.youtube.com/watch?v=6EUk6pqb1Po) — civilogy
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/pile-vs-shallow-conditions
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-8

## Question

What are the conditions (circumstances) where a pile foundation is more suitable than a shallow foundation?

## Short answer

Pile foundations are used where surface soils are weak, compressible, expansive, or collapsible and a firm layer lies at depth. They are also needed for heavy loads, uplift/lateral forces, high water tables, scour risk, unacceptable settlement, or when future excavations may undermine shallow footings.

## Answer

A **pile foundation** transfers loads to deeper, stronger strata or by shaft friction. It is preferred over a shallow foundation in the following conditions.

1. **Weak surface soil:** the top layers (soft clay, loose sand, fill, peat) are too weak or compressible, and a firm layer, rock or dense sand lies at a reasonable depth below.
2. **Heavy loads:** large column loads, such as tall buildings, bridges and silos, that need more area than shallow footings can give (footings would overlap).
3. **Uplift and lateral loads:** structures with tension (transmission towers, offshore platforms) or large horizontal loads, e.g. from wind, waves or earthquakes, such as retaining structures and quays.
4. **High water table or scour:** where excavation for a shallow footing is difficult, or river-bed scour may remove the soil near the surface (bridge piers).
5. **Expansive or collapsible soil:** piles pass through the active zone to stable soil.
6. **Excessive settlement of shallow foundations:** where settlement or differential settlement would be unacceptable.
7. **Neighbouring excavation or future excavation:** when the soil near the structure may be removed.
8. **Compaction of loose granular soil** by driven piles, or where shallow foundations in deep soft soil are uneconomical.

## Check yourself

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

1. Piles are preferred when:
   A. Surface soil is weak and a firm layer lies at reasonable depth
   B. Surface soil is hard rock
   C. Loads are light
   D. No groundwater
   Answer: A. Piles carry load past weak layers to firm strata. (Key point: Weak surface soil)

2. Which loading favours piles?
   A. Purely vertical small loads
   B. Uplift and large horizontal loads
   C. Temporary loads
   D. Light partitions
   Answer: B. Piles resist tension and lateral loads (towers, quays). (Key point: Uplift and lateral)

3. Why are piles used for bridge piers in rivers?
   A. River-bed scour may remove surface soil
   B. Concrete is cheaper
   C. Piles float
   D. Water is clean
   Answer: A. Piles extend below scour depth. (Key point: Scour)

4. In expansive or collapsible soil, piles are used to:
   A. Pass through the active zone to stable soil
   B. Increase swelling
   C. Replace the soil
   D. Reduce pile length
   Answer: A. They transfer load beyond the unstable zone. (Key point: Problem soils)

## 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
- [Pile spacing for 100% efficiency, 16 piles](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-spacing-100-efficiency-square-30cm) — Foundation Engineering, chapter 8, asked 2×
- [Types of pile by use; tension piles](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-types-use-tension) — Foundation Engineering, chapter 8
- [Pile group 16 piles of 50 cm, efficiency](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Apile-group-16-piles-50cm) — Foundation Engineering, chapter 8
- [Shallow versus deep foundation](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Ashallow-vs-deep-foundation) — Foundation Engineering, chapter 1

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- [Piles for Foundations: suitability for apartments](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Apiles-for-foundations-apartments) — Communication English, chapter 2
- [Types of shallow foundation](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ashallow-foundation-types) — Building Technology, chapter 2