Culverts Types, Design, Installation and Materials
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An opening through an embankment for the conveyance of water by mean of pipe or an enclosed channel.
It is a transverse and totally enclosed drain under a road or railway.
Type of Culverts
Pipe culverts are made of smooth steel, corrugated metal, or concrete material. Their primary purpose is to convey water under roads, although a variety of wildlife uses them as passageways. Pipe culverts typically range from 1- 6 feet in diameter and are the least expensive type of culvert. Round culverts are best suited to medium and high stream banks.
Pipe-arch culverts provide low clearance, openings suitable for large waterways, and are more aesthetic. They may also provide a greater hydraulic advantage to fishes at low flows and require less road fill.
Box culverts are used to transmit water during brief runoff periods. Theses are usually used by wildlife because they remain dry most of the year. They can have an artificial floor such as concrete. Box culverts generally provide more room for wildlife passage than large pipe culverts. Box culverts are usually made up of Reinforced Concrete (RCC)
Materials used for arch culverts are RCC, Corrugated Metal or Stone Masonry.
Design of Reinforced Concrete Culverts
Ideally, the axis of a culvert should coincide with that of the natural streamed and the structure should be straight and short. This may require modification of the culvert alignment and grade. Often it is more practical to construct the culvert at right angles to the roadway. However, the cost of any change in stream channel location required to accomplish this should be balanced against the cost of a skewed alignment of the culvert, and changes in channel hydraulics should be considered.
The culvert invert gradient should be the same as the natural streambed to minimize erosion and silting problems. Foundation settlement should be countered by cambering the culvert to ensure positive drainage.
It is often necessary to enlarge the natural channel a considerable distance downstream of the culvert to prevent backwater from entering the culvert. Also, enlargement of the culvert entrance may be required to prevent pending above the culvert entrance. The entrance and outlet conditions of the culvert structure directly impact its hydraulic capacity. Rounding or beveling the entrance corners increases the hydraulic capacity, especially for short culverts of small cross section. Scour problems can occur when abrupt changes are made to the streamed flow line at the entrance or outlet of the culvert.
Materials to be used for the culvert pipe foundation should be indicated on the drawings. Refer to the geotechnical foundation report for the project.
Bedding class and materials for culverts should be indicated on the drawings. When designing the bedding for a box culvert, assume the bedding material to be slightly yielding, and that a uniform support pressure develops under the box section.
Purpose and Use