Hydraulic Design of Highway Culverts - DOT On-Line Publications

Culvert shapes are as important in cost evaluations as culvert materials (Figure I-4). Many
shapes can be produced from a variety of materials; other shapes require certain materials.
Circular culverts are the most common shape. They are generally reasonably priced, can
support high structural loads, and are hydraulically efficient. However, limited fill height may
necessitate the use of a pipe-arch, ellipse, or an arch. Pipe-arches and ellipses are more
expensive than circular pipes, especially if the fill height is substantial. Arches require special
attention to their foundations, and failure due to scour is a concern. However, arches do
provide a natural stream bed which is an advantage for fish passage. Structural plate conduits
can be constructed in a variety of shapes, quickly, with low transport and handling costs (Figure
VI-24). Box culverts also possess flexibility in rise to span ratios by using multiple cells (Figure
VI-25). Precast box sections overcome the disadvantage of longer construction times which are
associated with cast-in-place installations; however handling costs are increased.
Inlet improvements on culverts provide an opportunity for additional cost savings. When a
culvert is operating in inlet control, the barrel does not flow full. By improving the inlet
configuration, a decrease in barrel size and overall culvert cost is possible. The savings on the
reduced barrel size usually outweighs the construction costs of the improved inlet. However,
the cost of excavation through rock or difficult material for enlarged slope-tapered inlets or
depressed side-tapered inlets should be considered.
Figure VI-24--Corrugated Metal Box Culvert (Contech)
165