Cofferdams in Building and Construction

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is a primary use of braced cofferdams?

Excavation of tunnels

Construction of buildings in deep water

Construction of bridge piers in shallow water (correct)

Demolition of old structures

What is an advantage of using steel sheet piles in cofferdams?

They can only be used once

They are very expensive

They are only suitable for shallow water

They are easily installed and removed (correct)

What is a limitation of cofferdams?

They require special equipment (correct)

They are quick to install

They are very cheap

They can be used in any environment

What is a typical component of a cofferdam?

Bearing piles Signup and view all the answers

What is a characteristic of steel sheet piles?

They are moderately watertight Signup and view all the answers

What is a necessary piece of equipment for installing cofferdams?

Pile driving hammer Signup and view all the answers

What is a typical application of cofferdams?

Constructing bridge piers Signup and view all the answers

What is a purpose of the bracing frame in a cofferdam?

To provide lateral support to the sheet piling Signup and view all the answers

What is the primary purpose of an underwater concrete seal course in cofferdam construction?

To seal off the water and resist its pressure Signup and view all the answers

What is the first step in the typical cofferdam construction sequence?

Pre-dredge to remove soil or soft sediments Signup and view all the answers

What is the purpose of blocking between the bracing frame and sheets?

To provide ties for sheet piles at the top Signup and view all the answers

What is the function of a tremie in cofferdam construction?

To deposit concrete under water Signup and view all the answers

Why is it necessary to drive bearing piles in cofferdam construction?

To create a stable foundation Signup and view all the answers

What is the purpose of rock fill in cofferdam construction?

To level and support the cofferdam Signup and view all the answers

Why is it necessary to excavate inside the grade in cofferdam construction?

To create a stable foundation Signup and view all the answers

What is the purpose of setting steel sheet piles in cofferdam construction?

To create a barrier against the water Signup and view all the answers

What is a crucial consideration when planning the removal of a cofferdam?

The effect of removal on the permanent structure Signup and view all the answers

Why are sheet piles often cut off and left in place during cofferdam removal?

To prevent damage to the foundation soils Signup and view all the answers

What is a key aspect of ensuring safety during cofferdam construction?

Monitoring the behavior of the cofferdam and surrounding area Signup and view all the answers

What is a characteristic of a double skin cofferdam?

Two parallel rows of sheet piles with a filling material Signup and view all the answers

What is a primary concern during the installation of a cofferdam?

The loads imposed by construction equipment and operations Signup and view all the answers

What is a critical aspect of cofferdam construction?

Verification that the structure is being constructed as planned Signup and view all the answers

What is the primary purpose of a cofferdam?

To keep water and/or soil out of an excavation area Signup and view all the answers

What is the main function of a cofferdam in relation to the construction of a bridge pier?

To create a dry work environment for the construction of the bridge pier Signup and view all the answers

What type of material is commonly used to construct a cofferdam?

Interlocking steel sheet piles Signup and view all the answers

What is a major challenge in constructing a cofferdam?

Maintaining close tolerances Signup and view all the answers

What is the interaction between the cofferdam and its environment?

The structure interacts with both the soil and water Signup and view all the answers

What is the purpose of pumping out the enclosed area within a cofferdam?

To create a dry work environment Signup and view all the answers

What is the significance of ground anchors in the construction of a cofferdam?

They are used to tie back the interlocking steel sheet piles Signup and view all the answers

What is the ultimate goal of constructing a cofferdam?

To allow the construction of a bridge pier in a dry work environment Signup and view all the answers

Study Notes

Cofferdams

A temporary structure designed and constructed to keep water and/or soil out of an excavation area in which a bridge pier or other structure or structural component is constructed.
A cofferdam is a temporary enclosure built within or in pairs across a body of water, constructed to allow the enclosed area to be pumped out, creating a dry work environment for major work to proceed.

Types of Cofferdams

Single skin cofferdams: consist of a single row of sheet piles forming an almost watertight box.
Double skin cofferdams: self-supporting gravity structures constructed by using two parallel rows of sheet piles with a filling material placed in the void created.
Braced cofferdams: formed from a single wall of sheet piling driven into the ground to form a box around the excavation area, braced on the inside, and dewatered.

Advantages of Cofferdams

Allow excavation and construction of structures in otherwise poor environments.
Provide a safe environment to work.
Contractors typically have design responsibility.
Steel sheet piles are easily installed and removed.
Materials can typically be reused on other projects.

Limitations of Cofferdams

Special equipment required.
Relatively expensive.
Typically very time-consuming and tedious.
Steel sheet piles sometimes driven out of lock.

Installation Requirements

Pile driving hammer; vibratory or impact.
Crane of sufficient size.
Steel sheet piles.
H piles and/or wide flange beams for wales and stringers.
Barges may be required.

Steel Sheet Pile Properties

Moderately watertight.
High shear and bending strength.
High interlock strength.
Easy to install and remove.
Reusable.
Can be cantilevered but typically require additional structural member (waling and cross bracing).

Typical Cofferdam Components

Sheet piling.
Bracing frame.
Concrete seal.
Bearing piles.

Typical Cofferdam Construction Sequence

Pre-dredge to remove soil or soft sediments and level the area of the cofferdam.
Drive temporary support piles.
Temporarily erect bracing frame on the support piles.
Set steel sheet piles, starting at all four corners and meeting at the center of each side, and drive sheet piles to grade.
Excavate inside the grade or slightly below grade, while leaving the cofferdam full of water.
Drive bearing piles.
Place rock fill as a levelling and support course.
Place tremie concrete seal.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

This quiz covers the role, advantages, and limitations of cofferdams in building and construction. It also explains their installation process. Coffer dams are temporary structures designed to keep water and soil out of excavation areas.