---
title: "Cellular cofferdam"
subject: "Foundation Engineering"
chapter: 5
key: "semester_5/foundation_engineering:cellular-cofferdam"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/cellular-cofferdam
site: BCT Engineering
---

# Cellular cofferdam

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

- Asked in: 2078 Bhadra, 2 marks
- Video: [Cofferdams Uses, Types, Construction, and Removal | Marine Construction Series #4](https://www.youtube.com/watch?v=mi3zKuhtEG4) — Pile Buck
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/cellular-cofferdam
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-5

## Question

Define cofferdam and explain the cellular cofferdam with the help of a neat sketch.

## Short answer

A cofferdam is a temporary enclosure pumped dry for underwater construction. A cellular cofferdam consists of interconnected steel sheet pile cells filled with granular soil, forming a self-supporting gravity wall. It resists water pressure by its own weight, eliminating internal bracing, and is used for piers, locks, and dams in deep water.

## Answer

A **cofferdam** is a temporary enclosure built in water or water-bearing ground, pumped dry to allow construction below water level.

A **cellular cofferdam** consists of a row of connected cells made of interlocking flat-web steel sheet piles, filled with sand, gravel or rock fill. Cells may be circular, diaphragm (arcs with cross walls) or cloverleaf.

```text
   Plan:  ( )( )( )( )    Section:  | fill |
           circular cells            |      |  ~~~ water
        joined by connecting arcs    |______|    (dry on right)
```

- The sheet piles act in tension (ring tension) and hold the fill; the filled cell behaves as a **gravity wall** resisting water pressure by its own weight.
- It is self-supporting, so no internal bracing blocks the working area.
- Stability is checked for sliding, overturning, interlock tension (hoop tension $T = p\,r$), shear along the centre line of the cell, and bearing.
- Uses: piers, locks, dams, deep water work; reusable and quick.

## Check yourself

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

1. What is a cellular cofferdam made of?
   A. Timber boxes filled with stone
   B. Connected cells of interlocking steel sheet piles filled with sand, gravel or rock
   C. A clay core embankment
   D. Braced sheet piles without fill
   Answer: B. Cells of interlocking flat-web sheet piles are filled with granular fill. (Key point: Cellular cofferdam composition)

2. How does the filled cell resist water pressure?
   A. By struts across the cell
   B. By anchors only
   C. By tension of the water
   D. As a gravity wall by its own weight, with sheet piles in ring tension
   Answer: D. The fill gives weight; sheet piles hold the fill in hoop tension T = p r. (Key point: How it resists)

3. Which is checked in cellular cofferdam stability?
   A. Only tensile strength of timber
   B. Sliding, overturning, interlock tension, centre-line shear and bearing
   C. Only plate settlement
   D. Only seepage
   Answer: B. Its stability checks include sliding, overturning, interlock tension, shear along the cell centre line and bearing. (Key point: Stability checks)