A culvert is a channel or drain passing under an embankment, usually for the purpose of draining water from one side of the embankment to the other. Lately, culverts have come to mean more than just simple drainage pipes, as the culvert has developed into precast concrete structures that can be driven upon.
Corrugated Metal Pipe Arch
This type of culvert was introduced in the 1960s and features a flat bottom and a circular top with sharp corner plates. This culvert allows water to move more efficiently than through a round shape. The steel plates have to be bolted together in the field. This type of culvert is dependent upon the quality of the backfill behind the metal, which gives the culvert its strength. Problems with the backfill can cause the culvert to settle unevenly or to develop cracks in the corner plates.
Four-Sided Precast Concrete Box
This culvert began popping up in the 1970s. The culvert is usually designed in spans ranging from 6 to 12 feet, built off-site and installed using tongue and groove joints. Many of these types of culverts are waterproofed during construction. The foot-thick walls of these culverts make them less reliant on backfill, but it's still necessary to keep the roadway from settling too low on either side of the culvert. They need less maintenance and are considered more efficient than their corrugated metal brothers.
These culverts feature models with a bottom or without a bottom and have been used in some areas since the mid-1980s. Like the steel plate culverts, these culverts are built in the field and are somewhat circular in shape. They are more durable because of the aluminium, and they respond better to backfill, but they require more work because footers must be excavated, formed and poured prior to installation.
Three-Sided Precast Concrete Box
This culvert eliminates the bottom span of the concrete box, which makes the culvert easier to move from off-site construction to on-site installation. This culvert can also be modified into either a flat-top or a curved-top culvert. The flat tops don't need backfill, while the curved tops do. Like the four-sided box, these can be driven upon.
Proper maintenance is important for maintaining a culvert and getting the best performance out of it. Erosion is a big issue, since the culvert's primary function is to help the movement of water from one place to another. The interior of culverts should always be clean, including the removal of debris and foreign materials from the inlet leading to the culvert. Trees should not be allowed to grow into the area around the culvert, especially on an embankment.