How Are Bridges Built Over Seas and Rivers?
Bridges are iconic symbols of human engineering prowess, combining functionality and aesthetic beauty. Among the most awe-inspiring feats of bridge construction are those built across seas and rivers, where the challenges of deep water make the process even more remarkable. In this article, we will explore the methods and engineering behind bridge construction over water.1
Conquering the Water: Challenges and Solutions
When the water being built over is shallow, constructing a bridge is relatively straightforward. Engineers create a temporary foundation on which piers are built to support the upper structure.2 However, when faced with deep water, the engineering becomes considerably more complex. Deepwater bridge construction calls for advanced techniques that seem nothing short of magical.
The Three Main Methods
There are three primary methods for bridge construction over deep water: battered piles, cofferdams, and caissons. Each method has its own set of advantages and complications, and the choice depends on site conditions and available technology.
1. Battered Piles
2. Cofferdams
A remarkable technique for bridge construction over deep water is the use of cofferdams. Cofferdams are created when a number of large piles are driven into the water, forming an enclosed space. Then, the water within this space is pumped out, leaving a dry and safe environment for construction work.
This method, although seemingly simple, requires meticulous engineering to prevent flooding or structural collapse, which could endanger workers’ lives. The key challenge is that water can seep up from the ground when the water on one side is pumped out, potentially destabilizing the structure. Therefore, the piles must be driven to a specific depth, determined by the type of soil at the bottom and observations of the water table.
Sometimes, in addition to pumping out the initial water, ongoing pumping is needed to continuously remove any seeping water. The decision to use this method depends on factors like cost and the feasibility of driving the piles to the correct depth.
3. Caissons: An Underappreciated Technique
Safety Measures and Historical Insights
While the construction of cofferdams might sound perilous, strict safety measures are typically in place, particularly concerning weather conditions. If the weather conditions are unfavorable, construction workers are not allowed to enter the cofferdam area. Additionally, protocols exist to evacuate workers promptly in the event of adverse conditions or emergencies.
