TM 5820-4/AFM 88-5, Chap 4
PIPE STRENGTH, COVER, AND BEDDING
roughness n to use in a given situation. The ques-
C1. General. A drainage pipe is defined as a
tion of whether n should be based on the new and
structure (other than a bridge) to convey water
ideal condition of a pipe or on anticipated condi-
through a trench or under a fill or some other
tion at a later date is difficult to answer. Sedi-
obstruction. Materials for permanent-type instal-
mentation or paved pipe can affect the coefficient
lations include non-reinforced concrete, rein-
of roughness. Table B3 gives the n values for
forced concrete, corrugated steel, asbestos-ce-
smooth interior pipe of any size, shape or type and
ment, clay, corrugated aluminum alloy, and
for annular and helical corrugated metal pipe both
structural plate steel pipe.
unpaved and 25 percent paved. When n values other
C-2. Selection of type of pipe.
than those listed are selected, such values will be
amply justified in the design analysis.
a. The selection of a suitable construction con-
duit will be governed by the availability and suit-
C-4. Restricted use of bituminous-coated pipe.
ability of pipe materials for local conditions with
Corrugated-metal pipe with any percentage of bi-
due consideration of economic factors. It is desir-
tuminous coating will not be installed where sol-
able to permit alternates so that bids can be re-
vents can be expected to enter the pipe. Polymeric
ceived with contractor's options for the different
coated corrugated steel pipe is recommended where
types of pipe suitable for a specific installation.
solvents might be expected.
Allowing alternates serves as a means of securing
bidding competition. When alternate designs are
advantageous, each system will be economically
C5. Minimum cover.
designed, taking advantage of full capacity, best
a. In the design and construction of the drain-
slope, least depth, and proper strength and in-
age system it will be necessary to consider both
stallation provisions for each material involved.
minimum and maximum earth cover allowable on
Where field conditions dictate the use of one pipe
the underground conduits to be placed under both
material in preference to others, the reasons will
flexible and rigid pavements. Underground con-
be clearly presented in the design analysis.
duits are subject to two principal types of loads:
b. Several factors should be considered in se-
dead loads (DL) caused by embankment or trench
backfill plus superimposed stationary surface loads,
lecting the type of pipe to be used in construction.
The factors include strength under either maxi-
uniform or concentrated; and live or moving loads
(LL), including impact. Live loads assume increas-
mum or minimum cover being provided, pipe bed-
ing importance with decreasing fill height.
ding and backfill conditions, anticipated loadings,
length of pipe sections, ease of installation, re-
b. AASHTO Standard Specifications for High-
sistance to corrosive action by liquids carried or
way Bridges should be used for all H20 Highway
surrounding soil materials, suitability of jointing
Loading Analyses. AREA Manual for Railway
methods, provisions for expected deflection with-
Engineering should be used for all Cooper's E 80
out adverse effect on the pipe structure or on the
Railway Loadings. Appropriate pipe manufac-
joints or overlying materials, and cost of main-
turer design manuals should be used for maxi-
tenance. Although it is possible to obtain an ac-
mum cover analyses.
ceptable pipe installation to meet design require-
c. Drainage systems should be designed in order
ments by establishing special provisions for several
to provide an ultimate capacity sufficient to serve
possible materials, ordinarily only one or two al-
the planned installation, Addition to, or replace-
ternates will economically meet the individual re-
ment of, drainage lines following initial construc-
quirements for a proposed drainage system.
tion is costly.
of in-place drainage and ero-
C-3. Selection of n values. A designer is con-
sion control facilities at 50 military installations
tinually confronted with what coefficient of