Bridge construction is inherently complex, but involve water and it gets even more demanding. With the need for underwater support, expert construction practices become even more essential. Here’s how bridges are constructed over water: from key considerations to the different methods employed.
What Are Key Considerations for Building a Bridge Over Water?
The Depth of the Water
Shallow water can allow for the creation of more simple, sometimes temporary, foundations that can support construction. A bridge construction expert can advise if water is shallow enough for this course of action.
The Size of the Body of Water
If the body of water is small enough, there’s the possibility that it can be removed entirely to avoid having to build over it (notwithstanding any conflicts with wetland protection acts). This is only possible in certain cases, and even some smaller bodies of water may only be displaced instead (this is also subject to any existing legislation). In addition to this/generally speaking, the narrower the body of water, the easier construction will be.
Surveying
Surveying both pieces of land that the bridge will connect and the underwater subsurface is crucial to determining a bridge’s abutments (vertical, pre-fabricated steel or concrete supports that connect the ground and deck of the bridge at its ends) are placed correctly. If they’re not at the right distance or elevation apart from each other, they’ll not work as needed.
Erosion Control and Conservation BMPs
It’s crucial to follow best management practices and ensure minimal environmental impact. This includes:
- Only using approved materials
- Having all necessary permits in place
- Enacting plans for stormwater pollution prevention
- Employing erosion control devices/barriers and spill containment equipment
Three Methods of Building a Bridge Over Water
There are three core ways to construct over-water bridges. When a leading bridge construction company undertakes them, they’re all effectively able to stand up to water currents, inclement weather conditions and the effects of time.
Battered Piles
The most popular means of construction for smaller bridges in shallower water, battered poles are large foundational poles made of concrete and steel. Using pile drivers, they’re driven into the soil underwater at an inward or outward angle to support a lateral load (the process itself isn’t too dissimilar to how a hammer drives a nail). This makes batter piles especially good at resisting sideways waves, winds and other hazards. Pile caps are then constructed over them, and they can then effectively support the necessary loads for upper bridge construction.
Cofferdams
This is the preferred construction method when water needs to be displaced. A cofferdam is a temporary water control method that allows the construction of the bridge’s substructure work, such as seismic piles & bridge abutments. It holds back water from an underwater construction site, via the creation of a watertight barrier from which water is then mechanically pumped out. This creates an optimal workspace with no leak concerns when done correctly. In shallow water, this can be done by using soil to create a berm or embankment around the construction site (though this has the potential of collapse if not done with the utmost professionalism).
During deep water construction, cofferdams are constructed from interlocking sheet piles and steel plates to create a waterproof chamber. They’re then rocket socketed into the ground to ensure a water-free barrier. After construction ends, they’re often dismantled and removed.
Culverts
Culverts are multi-purpose, highly malleable tunnel structures that aren’t always used as bridges (among other things, they’re ideal passageways for storm and wastewater). In the right circumstances and with a few modifications, though, culverts can serve travel needs. They’re highly effective, maintainable and affordable as replacements for short-span bridges that are no longer performing properly.
3-sided culverts are a common choice since they don’t impact natural streambeds (box culverts won’t either if they have infilling material at the bottom of their structures). Often precast from a mix of reinforced concrete and steel, there’s no need for underwater construction as they’re buildable right into foundations laid under the ground/soil on both ends. This means less time and labor requirements, but also that they have very specific size limitations. Culverts max out at a length and height of 20 feet, so they can only span small waterways.
Get the Best Bridge Construction for Your Water Circumstances With Northern Construction
To construct the best over-water bridge, it’s essential to work with experts who can understand your unique circumstances and what construction method best lines up with them. Northern Construction has served northeast bridge construction projects for over 25 years with expertise and results that stand the test of time. To get started, give us a call or fill out a contact form and request a quote today.