Hydraulic Design of Highway Culverts - DOT On-Line Publications

G. Circular Pipe Culverts
1. Design Procedures. Design procedures and criteria are available for side-and slopetapered
inlets for circular pipe culverts. The inlet designs are shown in Figure IV-12. For the
side-tapered inlet, either prefabricated inlets with nonrectangular cross sections or cast-in-place
rectangular inlets are used. The rectangular inlets are joined to the circular pipe using a square
to circular throat transition section.
Figure IV-12--Tapered Inlets for Pipe Culverts
For slope-tapered inlets, the rectangular designs (vertical or mitered face) are the only option for
which design charts are available. The square to circular transition section is used to join the
slope-tapered inlet to the circular pipe.
a. Side-Tapered Inlets. The throat and face control design nomographs for side-tapered inlets
on circular pipe culverts are in Appendix D. For throat control, there are two scales on the
nomograph: one for smooth inlets and one for rough inlets. The difference in headwater
requirement is due to the hydraulic resistance between the face and the throat of the inlet.
The design nomograph for sizing the face of a side-tapered inlet with a nonrectangular face
includes three scales. Each scale is for a different edge condition, including thin-edge
projecting, square edge, and bevel edged. The face area is larger than the barrel area and may
be any nonrectangular shape, including an oval, a circle, a circular segment, or a pipe-arch. To
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