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 111 0-2-2902
S Mar 1969

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Where conduits or culverts are designed for railroads or highways, the loading and other
design criteria will generally be required to satisfy the requirements of the affected railroad com-
pany or state highway commission. These requirements are usually closely related to those of
the AREA Manual or the AASHO Standard Specifications for Highway Bridges. Where applica-
ble, impact loading should be considered.

d. Loading conditions dWl to backfiU. The behavior of the soil pressures transmitted to a con-
duit or culvert by the overlying fill material is influenced by the physical characteristics and de-
gree of compaction of the soil above and adjacent to the conduit or culvert as well as the
degree of flexibility and the amount of settlement of the conduit or culvert. The effect of sub-
mergence in the backfill must also be considered as indicated on plate 4. Direct measurements of
such pressures have been made, as for example the field tests conducted by AREA at Farina,
Illinois, and those performed at the University of North Carolina and at Iowa State University.
However, these investigations were limited to tests on small diameter pipes under relatively low
fills. Until more data are available, the following loading should be used for rigid conduits and
culverts for dams and levees and outlet conduits for interior drainage.
(1) Conditwn I applies to those structures that are completely buried in a ditch with
no superimposed fill above the top of the ditch. To satisfy this condition, the width of the
trench, measured at the top of the conduit or culvert, shall be no greater than one and one-half
times the overall width of the conduit or culve rt and the sides of the ditch above the top of the
conduit shall have a slope no flatter than one horizontal to two vertical. This condition is iIlus-
trated on plate 3. The total dead load of the earth at the top of the conduit should be computed
as the larger of the two values obtained from the following equations:

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W, = Cd y b? _ _ _ _ _ _ __ __ _ _ __ __ __ _ _ __ _ __ _ __ _ _ __ _ __ _ __ __ __ __ __ _ __ __ _ _ _ _ h _ __ __ (2)

values of Cd being taken from the curves on Plate 10, or

W, = yb,H

________________ _______________________________________(8)

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When the height of the fiill above the top of the conduit, (H.). is less than twice the ditch width,
the horizontal pressure should be assumed to vary with the depth over the height of the conduit.
When H,. is equal to or greater than 2bd, the horizontal pressure may be computed at the center
of the conduit using an average value of H equal to Hh applied uniformly over the height of
the conduit. When H,<2bd, the horizontal pressure in pounds per square foot at any depth should
be computed from the formula:

P, = yHtan' (450 - </>) _______________________________________(4)
2'

In most cases, the unit weight, y, and the internal friction angle, </>, of the proposed backfill
material in dry, natural drained and submerged conditions should be determined by the labora-
tory and adapted to the design. However, where economic conditions do not justify the cost of
extensive investigations by a soils laboratory, appropriate values of unit weight of the material
and its internal friction angle should be determined by consultation with the soils engineer.

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The values of tan' (450 - </>) for use in equation 4.for various values of </> are given in table
2'

1, below.

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