Underwater Constructions | How do Engineers Make Them?

Summary

This video script delves into the intricate process of underwater bridge construction using coffer dams. It explains how engineers build temporary dams to exclude water, drive sheet piles into bedrock, and conduct geotechnical studies to ensure soil can support the structure. The script also highlights the importance of bracing frames to prevent inward collapse and the use of concrete seal courses to block water seepage. Finally, it details the construction of the bridge pier and the eventual removal of the coffer dam, showcasing the challenges and solutions in civil engineering's underwater projects.

Takeaways

• 🌊 Engineers use coffer dams to perform underwater construction by creating a dry work area.
• 🔨 Guide piles and sheet piles are essential for building coffer dams, with interlocking sheet piles minimizing water leakage.
• 🚧 The pile driving hammer uses vibration rather than force to push the sheet piles into the soil, ensuring stable penetration to the bedrock.
• 🧪 A cone penetration test is used to measure soil resistance and determine how deep sheet piles should be driven to reach the bedrock.
• 💧 Water pressure on both sides of the coffer dam initially cancels out, but once the water inside is removed, bracing frames must be added to prevent inward collapse.
• 🏗️ A double-layered coffer dam, filled with granular material between sheet piles, provides extra resistance to water leakage.
• 🪜 A concrete seal course is poured at the base after removing soil, providing a waterproof foundation and stability for the construction.
• 🚢 Specialized machinery like clamshell buckets and vibrating hammers are crucial to underwater excavation and pile installation.
• 🔧 Reinforced steel bars and high-quality concrete are used to construct the bridge pier, ensuring it can withstand water pressure and heavy loads.
• ✂️ Once the bridge pier gains sufficient strength, the coffer dam is removed, with sheet piles cut just below the concrete seal to preserve structural integrity.

Q & A

What is the primary challenge faced by laborers during the construction of an underwater bridge?

The primary challenge is fighting against violent ocean currents while constructing the bridge and ensuring the structure is stable and secure.

What is a coffer dam and why is it used in underwater construction?

A coffer dam is a temporary structure used to exclude water from the construction site, allowing work to be carried out in a dry environment.

How are guide piles used in the construction of a coffer dam?

Guide piles are erected first to provide guidance for the construction of the coffer dam, ensuring proper alignment and structure.

What is the purpose of sheet piles in coffer dam construction?

Sheet piles are driven into the soil to create a watertight barrier. Their interlocking connections help minimize water leakage.

Why does the pile driving hammer machine use vibration instead of pushing force?

Vibration helps to penetrate the soil more effectively and with less resistance, reducing the risk of damage to the sheet piles and the surrounding environment.

What is the role of a barge in underwater construction?

A barge is used to transport machinery and components required at the construction site, facilitating the movement of heavy equipment.

Why is a geotechnical study important before constructing a coffer dam?

A geotechnical study helps to understand the soil's strength and characteristics, ensuring the coffer dam is built on a stable foundation that can support the structure's load.

What is a cone penetration test and how is it used in coffer dam construction?

A cone penetration test is an in-situ test that measures soil strength and resistance. It helps determine how deep the sheet piles need to be driven to reach bedrock.

Why did the coffer dam collapse in the script?

The coffer dam collapsed because the inward force acting on it was not counterbalanced by the water pressure once the water was pumped out.

How can the inward collapse of sheet piles be prevented?

The inward collapse can be prevented by erecting a bracing frame structure alongside the sheet piles, which provides lateral support and resistance to inward movement.

What is the concrete seal course technique and how does it help in underwater construction?

The concrete seal course technique involves pouring concrete on the hard strata to create a strong footing that prevents water leakage and provides a stable base for the structure.