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Consider the following statements: 1. A braced coffer dam is used in shallow trench excavation as well as in deep excavation exceeding 6 m in depth. 2. Coffer dams, braced or un-braced, are temporary structures either on land or in water bodies. 3. When sheet piling is used for retaining soil, or soil and water, without any bracing, it is called a bulkhead. Which of the above statements are correct?

Consider the following statements: 1. A braced coffer dam is used in shallow trench excavation as well as in deep excavation exceeding 6 m in depth. 2. Coffer dams, braced or un-braced, are temporary structures either on land or in water bodies. 3. When sheet piling is used for retaining soil, or soil and water, without any bracing, it is called a bulkhead. Which of the above statements are correct? Correct Answer 1, 2 and 3

Explanation:

Coffer dam is a temporary structure constructed on rivers, lake or land masses to keep the working area dry for construction of other structures and these are meant to be water tight.

In the shallow trench excavation, a cantilever sheet piling coffer dam otherwise, unbraced coffer dam is used.

Statement-II- True

Type of Coffer dam

When to Use

Earth Embankments

When no limitation on heights, and availability of space for construction.

Cantilever Sheet Pile

For small heights < 6 m

Double Wall Coffer Dam

Moderate heights

Braced Coffer heights

 For height of 6 to 12 m

Cellular Coffer dam

When head of water is > 20 m.

 

Statement III-True

 Bulkhead is sheet pile retaining wall when bracing is not provided and used to hold lateral movements.

 Bracing is lateral supporting system between two sheeting provided on both side of excavations.

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