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How do people build bridges that stand in water?

I live right by San Francisco and i've been wondering how are bridges built (like the bay bridge) underneath the ocean. How do they manage to get everything down there if oceans are so deep?

Public Comments

1. The upright columns are floated into place, and then sunk.
2. The History Channel also has a documentary on this.
3. Bridges over water are built on piers. The piers are poured as concrete upon a very solid underwater foundation, known as bedrock. A steel shell is placed on the bedrock in which concrete is poured. If the bedrock is deep, say a hundred feet, it takes hundreds of tons of concrete to create the pier.
4. Look up these two terms to help you obtain the knowledge on how bridges are built on water: - Caisson - Cofferdam I hope this helps
5. Engineers must dig deep into the earth to find a geologic formation that is strong enough to support the tremendous weight carried by the pillars of these bridges. The early work is to use small test borings to learn about the type of soil that underlies the ocean floor. Using that information, geotechnical engineers can determine how deep and how large the bridge pillar foundation must be. Then the task is to actually construct that foundation. In some cases large poles called piles are driven deep into the ocean floor. In other cases, caissons (see reference) must be use to provide a chamber where workers can excavate a hole into the ocean floor. Of course every case is different and the engineer who is clever enough to find an inexpensive way to build a solid foundation under the ocean is a highly respected person. Once the foundation is complete the task of building the bridge is far from complete. Every component of the bridge must be designed to withstand the forces of mother nature, ie, high wind, earthquakes, gravity. At the same time, construction must respect the environment to insure air pollution, water pollution and damage to sea life is held to a minimum.