Underwater Construction: Coffer Dams

Introduction

• Construction of underwater structures, focusing on coffer dams.
• Engineers avoid working directly in water by using temporary dams, called coffer dams, to remove water.

Building a Coffer Dam

Erecting Guide Piles

• First step: Erect guide piles with a pile driving hammer machine.
• Guide piles provide guidance for the coffer dam's construction.

Driving Sheet Piles

• Use the same machine to drive sheet piles into the soil.
• Sheet piles have interlocking connections to minimize water leakage.
• Driven until they reach bedrock, starting from the corner and moving inward.
• Pile driving hammer machine uses vibrations to penetrate the soil.

Barge Usage

• A barge is used to carry machinery and components to the construction site.

Water Pumping Phase

• Detailed geotechnical study of soil required before water pumping.
• The Cone Penetration Test measures soil strength by resistance values.
• Double sheet piles and granular material like sand are used to prevent water leakage.
• Removal of water without proper bracing can lead to collapse due to inward force.

Bracing Frame Structure

• Comprising whales, struts, and braces to provide lateral support and resist inward movement.
• Strong, secure structure allows water removal without collapse.

Addressing Water Seepage

• Water particles travel like a U below the coffer dam due to differential pressure.
• Continuous pumping needed to manage seepage.
• Concrete seal course technique used for strong footing and preventing water leakage.

Soil and Concrete Work

• Soil removal with clamshell bucket operated by an excavator.
• Concrete seal course constructed on hard strata using hollow steel pipes and pile driving machines.
• Use of tremie method for underwater concreting to prevent water contamination.

Bridge Pier Construction

• Reinforced bar skeleton laid out for bridge pier footing shaft.
• High-quality materials ensure durability against water pressure and bridge load.
• Concrete poured in the structure, takes 14-28 days to gain strength.

Removing the Coffer Dam

• Coffer dam removed after bridge pier gains strength.
• Sheet piles cut at level of concrete seal course to maintain structural integrity.

Conclusion

• Brief mention of other underwater construction techniques (e.g., ken, pile foundation).
• Encouragement to support via Patreon for future videos on those topics.