Figure 3-33.Standard drop manhole for sanitary or storm
BACKFILLING AND TAMPING
After all pipelines have been laid and tested, they
are ready to be covered; this process is known as
backfilling and tamping. The method described below
should work for sewer lines.
Figure 3-32.Test plugs and test tees.
Fine material, free from stones and other debris, is
tamped in uniform layers with a small hand- or air-
operated tamper under, around, and over the pipe. Use
a hand shovel to backfill the ditch until the pipe has a 2-
foot covering. This fill should be placed in the ditch
and tamped in 4-inch layers or less. It should proceed
evenly on each side of the pipe, so injurious side
pressure cannot occur. Make sure you do NOT walk on
the pipe until you have at least 1 foot of soil tamped
over the pipe. Until 2 feet of fill has been placed over
the pipe, the filling should be done carefully with hand
shovels; after that, machinery may be used for faster
backfilling. However, do not let the machinery run
over the line.
Normally, it is not your responsibility as a
Utilitiesman to construct manholes. They are made of
concrete or brick; however, you may be working with
the Builders in spotting the location for the manholes.
Figure 3-33 shows a typical drop manhole.
Watertight manholes are made of brick or
concrete, 4 feet in diameter at sewer level, and should
be placed at junctions and bends in the line. They are
spaced preferably 300 feet apart for 8-inch pipe, 400
feet apart for 10- to 15-inch pipe, 500 feet apart for 18-
to 48-inch pipe, and 600 feet apart for larger sizes.
Sewers should be laid straight to line and grade
between manholes, and changes in the size of sewer
lines must take place only at the manholes. The crown
of the outlet pipe from a manhole should be on a line
with or below the crown of the inlet pipe. When the
invert of the inlet pipe is more than 2 feet above that of
the outlet pipe, a drop manhole must be provided to
conduct the sewage to a lower level with minimum
Puddling, or flooding, with water to consolidate
the backfill should NOT be done for a sewer line. The
sections of pipe are in short lengths and tend to settle
very rapidly to form pockets or low spots in the line.
Q12. What is the required head height for a water