30 Questions
What is a primary use of braced cofferdams?
Construction of bridge piers in shallow water
What is an advantage of using steel sheet piles in cofferdams?
They are easily installed and removed
What is a limitation of cofferdams?
They require special equipment
What is a typical component of a cofferdam?
Bearing piles
What is a characteristic of steel sheet piles?
They are moderately watertight
What is a necessary piece of equipment for installing cofferdams?
Pile driving hammer
What is a typical application of cofferdams?
Constructing bridge piers
What is a purpose of the bracing frame in a cofferdam?
To provide lateral support to the sheet piling
What is the primary purpose of an underwater concrete seal course in cofferdam construction?
To seal off the water and resist its pressure
What is the first step in the typical cofferdam construction sequence?
Pre-dredge to remove soil or soft sediments
What is the purpose of blocking between the bracing frame and sheets?
To provide ties for sheet piles at the top
What is the function of a tremie in cofferdam construction?
To deposit concrete under water
Why is it necessary to drive bearing piles in cofferdam construction?
To create a stable foundation
What is the purpose of rock fill in cofferdam construction?
To level and support the cofferdam
Why is it necessary to excavate inside the grade in cofferdam construction?
To create a stable foundation
What is the purpose of setting steel sheet piles in cofferdam construction?
To create a barrier against the water
What is a crucial consideration when planning the removal of a cofferdam?
The effect of removal on the permanent structure
Why are sheet piles often cut off and left in place during cofferdam removal?
To prevent damage to the foundation soils
What is a key aspect of ensuring safety during cofferdam construction?
Monitoring the behavior of the cofferdam and surrounding area
What is a characteristic of a double skin cofferdam?
Two parallel rows of sheet piles with a filling material
What is a primary concern during the installation of a cofferdam?
The loads imposed by construction equipment and operations
What is a critical aspect of cofferdam construction?
Verification that the structure is being constructed as planned
What is the primary purpose of a cofferdam?
To keep water and/or soil out of an excavation area
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
What type of material is commonly used to construct a cofferdam?
Interlocking steel sheet piles
What is a major challenge in constructing a cofferdam?
Maintaining close tolerances
What is the interaction between the cofferdam and its environment?
The structure interacts with both the soil and water
What is the purpose of pumping out the enclosed area within a cofferdam?
To create a dry work environment
What is the significance of ground anchors in the construction of a cofferdam?
They are used to tie back the interlocking steel sheet piles
What is the ultimate goal of constructing a cofferdam?
To allow the construction of a bridge pier in a dry work environment
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.
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.
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