---
title: "Free earth versus fixed earth support"
subject: "Foundation Engineering"
chapter: 5
key: "semester_5/foundation_engineering:free-vs-fixed-earth-support"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/free-vs-fixed-earth-support
site: BCT Engineering
---

# Free earth versus fixed earth support

Foundation Engineering · Chapter 5: Flexible Retaining Structures and Coffer Dams

- Asked in: 2078 Bhadra, 2 marks
- Video: [FREE EARTH SUPPORT METHOD | SHEET PILE NUMERICAL | 2016 PU | FOUNDATION NUMERICAL | TU.PU.KU.POU](https://www.youtube.com/watch?v=fFNHzHOaEok) — Sudip Dhakal
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/free-vs-fixed-earth-support
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-5

## Question

Write down the differences between free earth and fixed earth support anchored pile.

## Short answer

Free earth support uses shallow embedment with freely rotating tip, larger bending moment, no contraflexure, and simple statics. Fixed earth support requires deeper embedment to fix the tip, introduces reverse curvature with a contraflexure point, smaller bending moment, and more complex analysis like equivalent beam method.

## Answer

| Point | Free earth support | Fixed earth support |
|---|---|---|
| Embedment depth | Shallow (smaller) | Deeper (larger) |
| Toe condition | Pile tip is free to rotate; no fixity | Pile tip is fixed against rotation (zero slope at the tip) |
| Passive pressure | Only in front of the pile; the pile acts as a simply supported beam between the anchor and the soil reaction | Passive pressure in front, and a counter (reverse) passive force behind the toe |
| Bending moment | Larger maximum moment | Smaller maximum moment (with a negative moment near the toe) |
| Deflected shape | One curve, no contraflexure | Has a point of contraflexure |
| Analysis | Simple statics, moments about the anchor | Equivalent beam (Blum) or other methods; more complex |

## Check yourself

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

1. Which statement about embedment is correct?
   A. Free earth is deeper
   B. Both need the same depth
   C. Fixed earth support needs deeper embedment
   D. Free earth needs no embedment
   Answer: C. Free earth support has shallower embedment; fixed earth support is deeper. (Key point: Embedment depth)

2. What is the toe condition in free earth support?
   A. Fixed with zero rotation
   B. Rigid
   C. Anchored in rock
   D. Free to rotate with no fixity
   Answer: D. In free earth the tip can rotate; in fixed earth the tip is fixed. (Key point: Toe condition)

3. How do maximum bending moments compare?
   A. Free earth has larger moment; fixed has smaller with negative moment near toe
   B. Fixed earth has larger moment
   C. They are the same
   D. Free earth has no moment
   Answer: A. Fixity at the toe reduces the maximum moment, with a negative moment near the toe. (Key point: Bending moment)

4. How is free earth support analysed?
   A. Equivalent beam only
   B. Simple statics with moments about the anchor
   C. Finite element only
   D. No analysis
   Answer: B. Free earth uses simple statics (moments about the anchor); fixed earth needs equivalent beam methods. (Key point: Analysis method)

## Related in Foundation Engineering

- [Anchored sheet pile, free earth procedure](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aanchored-sheet-pile-free-earth-procedure) — Foundation Engineering, chapter 5
- [Anchored sheet pile, free earth, with anchor pull](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Aanchored-sheet-pile-embedment) — Foundation Engineering, chapter 5

## Related in other subjects

- [Fixed beam: end moments from support rotation or settlement](https://www.bctengineer.com/question.md?key=semester_5%2Ftheory_of_structures_ii%3Afixed-beam-end-moments-rotation-settlement) — Theory of Structures II, chapter 3, asked 4×
- [ILD: moment at support B, fixed-propped beam](https://www.bctengineer.com/question.md?key=semester_5%2Ftheory_of_structures_ii%3Aild-moment-b-propped-2l-l) — Theory of Structures II, chapter 4
- [ILD: vertical reaction at fixed support](https://www.bctengineer.com/question.md?key=semester_5%2Ftheory_of_structures_ii%3Aild-vertical-reaction-fixed-propped-025) — Theory of Structures II, chapter 4
- [ILD: bending moment at fixed support, 10 m beam](https://www.bctengineer.com/question.md?key=semester_5%2Ftheory_of_structures_ii%3Aild-bm-fixed-support-10m-1) — Theory of Structures II, chapter 4