TM 5-820-3/AFM 88-5, Chap. 3
so that full pipe flow can never occur, in order to
spigot joints caulked with oakum or other similar
maintain the hydraulic gradient above the pipe
rope-type caulking materials and sealed with hot-
invert but below crown of the pipe, thereby
poured joint compound have also been successful.
reducing the tendency for infiltration of soil and
Metal pipe seams may require welding, and the
water through joints. Pipes on steep slopes may
rivet heads may have to be ground to lessen
tend to prime and flow full periodically because of
interference with gaskets. There are several kinds
entrance or outlet condition effects until the
of connecting bands which are adequate both
hydraulic or pressure gradient is lowered enough to
hydraulically and structurally for joining corrugated
cause venting or loss of prime at either the inlet or
metal pipes on steep slopes.
e. A conclusive infiltration test will be required
outlet. The alternating increase and reduction of
pressure relative to atmospheric pressure is con-
for each section of pipeline involving watertight
sidered to be a primary cause of severe piping and
joints, and installation of flexible watertight joints
infiltration. A vertical riser should be provided up-
will conform closely to manufacturers' recommen-
stream of or at the change in slope to provide suf-
dations. Although system layouts presently recom-
ficient venting for establishment of partial flow and
mended are considered adequate, particular care
stabilization of the pressure gradient in the portion
should be exercised to provide a layout of sub-
of pipe on the steep slope. The riser may also be
drains that does not require water to travel appre-
equipped with an inlet and used simultaneously to
ciable distances through the base course due to im-
collect runoff from a berm or adjacent area.
pervious subgrade material or barriers. Pervious
base courses with a minimum thickness of about 6
can be controlled by watertight flexible joint mate-
inches with provisions for drainage should be pro-
rials in rigid pipe and with watertight coupling
vided beneath pavements constructed on fine-
bands in flexible pipe. Successful flexible watertight
grained subgrades and subject to perched water
joints have been obtained in rigid pipelines with
table conditions. Base courses containing more
rubber gaskets installed in close-tolerance tongue-
than 10 percent fines cannot be drained and remain
and-groove joints and factory-installed plastic
saturated continuously.
gaskets installed on bell-and-spigot pipe. Bell-and-
2-11
Previous Page
