FLOOD06430

• County: Statewide
• Basin: Statewide
• Title: Conduits, Culverts and Pipes
• Date: 3/3/1969
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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EM 1110-2-2902

DEPARTMENT OF THE ARMY
Office of the Chief of Engineers
Washington, D.C. 20815

ENGCW-ED
Manual
No. 1110-2-2902

3 Mar 1969

ENGINEERING AND DESIGN

Conduits, Culverts and Pipes

1. Purpose and Scope. This manual discusses planning the structural design and construction of
conduits, culverts, and pipes through embankment type dams and levees and pressure conduits
for interior drainage of local flood protection projects, with particular emphasis on cast-in-place
conduits through embankment type dams. Because of the abundance of literature on the design
of pipes, this subject has been given limited coverage. The determination of superimposed loads
is discussed as well as the effects of variations in conduit shapes.

2. Applicability. This manual is issued for the guidance of divisions and districts having re-
sponsibility for Civil Works.

3. Conduit Shapes. The selection of the most economical conduit cross section must depend on the
designer's judgment and the consideration of all design factors and site conditions for each ap-
plication. For fills of moderate height, circular or rectangular openings will frequently be the
most practicable because of the speed and economy obtainable in design and construction. For
openings of less than about 60 square feet, a single rectangular box probably will be most eco-
nomical for moderate fills up to about 60 feet. However, a rectangular conduit entrenched in
rock to the top of the conduit may be economical for higher fills since the applied vertical load
need be only the weight of the earth directly above with no increase for differential fill settle-
ment. The ratio of height to width should be about 1.50 to accommodate the range of loading
conditions economically. Where there is a battery of outlet gates, a multiple-box shape is some-
times economical where acceptable from a hydraulic standpoint. For further discussion see ref-
erence (20).

For a single conduit of more than about 60 square feet area and with a fill height over 60 feet,
it will generally be found economical to use a section other than rectangular for the projection
loading condition. (Condition III). The circular shapes are more adaptable to changes in loadings
and stresses which may be caused by unequal fill or foundation settlement. For cases in which the
projection loading condition applies, no material stress reduction results from the provision of a
variable cross section. These structures should be formed as shown on plate 1 and should be ana-
lyzed as a ring of uniform thickness. While these sections show variations in thickness in the
lower half of the conduit due to forming and other construction expedients, such variations may
be disregarded in the design without appreciable error. However, it may be difficult to shape the
excavation in closely-bedded, flatlying.shale or rock with frequent shale interbeds. For this condi-
tion it may be economical to excavate the founda tion level and backfill to the desired shape with
low-cement concrete. For each project, the geologist should be consulted to determine what form
of excavation he considers most practicable to obtain. Lines shown on the drawings are often those
designated as pay excavation lines and not actual excavation lines. However, for conduits under
levees and dams, actual excavation lines rather than pay excavation lines should be shown and it
should be made clear that the Contractor must excavate to those lines.
The oblong section shown on plate 1 is formed by separating two semicircular sections by
short straight vertical wall sections. It generally achieves maximum economy of materials by

This Manual rescinds EM 1110-2-2902 (Part CXXIX, Chap. 2), June 1948.

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