---
title: "Anchored sheet pile, free earth procedure"
subject: "Foundation Engineering"
chapter: 5
key: "semester_5/foundation_engineering:anchored-sheet-pile-free-earth-procedure"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/anchored-sheet-pile-free-earth-procedure
site: BCT Engineering
---

# Anchored sheet pile, free earth procedure

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

- Asked in: 2078 Kartik, 1+3 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/anchored-sheet-pile-free-earth-procedure
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-5

## Question

Enlist the uses of sheet pile. Write down the step by step procedure of analysis of anchored sheet pile by free earth support method in granular soil.

## Short answer

Sheet piles serve as waterfront walls, cofferdams, excavation support, and cutoff barriers. Free earth method: calculate Ka and Kp; plot active pressure over H+D and passive over D; sum moments about anchor to solve D; get anchor force from horizontal equilibrium; add 20–30% depth; then compute maximum bending moment and required section modulus.

## Answer

#### Uses of sheet piles
- Retaining walls for waterfront structures (quay walls, bulkheads, jetties).
- Temporary support of excavations (braced cuts and trenches).
- Cofferdams for bridge piers and underwater foundations.
- Cut-off walls under dams, seepage control, flood protection.
- Protection against scour and for river training, and landfill containment.

#### Free earth support method (granular soil)
Assumption: the pile tip is free to rotate (no fixity); the active pressure acts on the full height $(H+D)$ on the back, passive pressure acts only in front; the wall is simply supported by the anchor and the passive resistance.
1. Compute $K_a = \tan^2(45^\circ-\phi/2)$ and $K_p = \tan^2(45^\circ+\phi/2)$; use $\gamma'$ below water table and include surcharge and water pressure.
2. Draw the active pressure diagram on the back from top to depth $H+D$ and the passive pressure diagram in front from the dredge line to depth $D$ (using $K_p/FS$ if a factor of safety is applied to passive resistance).
3. Find the active resultant $P_a$ and its lever arm from the anchor level.
4. Find the passive resultant $P_p$ (in terms of $D$) and its lever arm from the anchor.
5. Take **moments about the anchor point**: $P_a\, l_a = P_p\, l_p$ and solve for the embedment $D$ (trial and error).
6. Find the anchor force per metre $T$ from horizontal equilibrium: $T = P_a - P_p$.
7. Increase $D$ by 20-30% for the design depth, then find the maximum bending moment (at zero shear) and select the sheet pile section from $Z = M_{max}/\sigma_{allow}$.

## Check yourself

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

1. Which is NOT a use of sheet piles?
   A. Waterfront bulkheads
   B. Cofferdams
   C. Cut-off walls under dams
   D. Supporting overhead transmission lines as the main foundation
   Answer: D. Sheet piles are used for waterfront walls, excavation support, cofferdams, cut-offs and scour protection. (Key point: Uses of sheet piles)

2. What is assumed at the pile tip in free earth support?
   A. Fixed with zero rotation
   B. Free to rotate, no fixity
   C. Embedded in rock
   D. Reverse passive force behind toe
   Answer: B. Free earth support assumes the tip is free to rotate and passive pressure acts only in front. (Key point: Assumption of the method)

3. Which equilibrium gives the embedment D?
   A. Vertical equilibrium
   B. Horizontal equilibrium alone
   C. Moments about the pile tip
   D. Moments about the anchor point: P_a l_a = P_p l_p
   Answer: D. Moments about the anchor, solved by trial and error, give D. (Key point: Solving for D)

4. How is T found after D?
   A. T = P_a - P_p from horizontal equilibrium
   B. T = P_a + P_p
   C. T = P_p
   D. T = 0.5 P_a
   Answer: A. Horizontal equilibrium gives T = P_a - P_p; then D is increased 20-30% for design. (Key point: Anchor force)

## Related in Foundation Engineering

- [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
- [Free earth versus fixed earth support](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Afree-vs-fixed-earth-support) — Foundation Engineering, chapter 5
- [Sheet pile and deflected shapes](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asheet-pile-deflected-shapes) — Foundation Engineering, chapter 5
- [Cantilever sheet pile, 5 m excavation](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Acantilever-sheet-pile-5m-sand) — Foundation Engineering, chapter 5

## Related in other subjects

- [Sheet pile flow net; graded filter](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Asheet-pile-flow-net-graded-filter) — Soil Mechanics, chapter 7
- [Flow net under sheet pile, discharge](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Asheet-pile-flow-net-steps-discharge) — Soil Mechanics, chapter 7