Overview of Culverts: shapes, materials and inletsArticles > Overview of Culverts: shapes, materials and inlets
A culvert is a hydraulically short conduit which conveys stream flow through a roadway embankment or past some other type of flow obstruction. Culverts are constructed from a variety of materials and are available in many different shapes and configurations. Culvert selection factors include roadway profiles, channel characteristics, flood damage evaluations, construction and maintenance costs, and estimates of service life.
1. Shapes. Numerous cross-sectional shapes are available. The most commonly used shapes, depicted in Figure below, include circular, box (rectangular), elliptical, pipe-arch, and arch. The shape selection is based on the cost of construction, the limitation on upstream water surface elevation, roadway embankment height, and hydraulic performance.
2. Materials. The selection of a culvert material may depend upon structural strength, hydraulic roughness, durability, and corrosion and abrasion resistance. The three most common culvert materials are concrete and nonreinforced), corrugated aluminum, and corrugated steel. Culverts may also be lined with other materials to inhibit corrosion and abrasion, or to reduce hydraulic resistance. For example, corrugated metal culverts may be lined with asphaltic concrete. A concrete box culvert and a corrugated metal arch culvert depicted in Figures I-5 and I-6 respectively.
3. Inlets. A multitude of different inlet configurations are utilized on culvert barrels. These include both prefabricated and constructed-in-place installations. Commonly used inlet configurations include projecting culvert barrels, cast-in-place concrete headwalls, precast or prefabricated end sections, and culvert ends mitered to conform to the fill slope (Figure I-7). Structural stability, aesthetics, erosion control, and fill retention are considerations in the selection of various inlet configurations.
The hydraulic capacity of a culvert may be improved by appropriate inlet selection. Since the natural channel is usually wider than the culvert barrel, the culvert inlet edge represents a flow contraction and may be the primary flow control. The provision of a more gradual flow transition will lessen the energy loss and thus create a more hydraulically efficient inlet condition (Figure I- 8). Beveled edges are therefore more efficient than square edges. Side-tapered and slopetapered inlets, commonly referred to as improved inlets, further reduce the flow contraction. Depressed inlets, such as slope-tapered inlets, increase the effective head on the flow control section, thereby further increasing the culvert efficiency. Figures I-9 and I-10 depict a sidetapered and a slope-tapered inlet respectively.
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