48
I-800
TRENCHING
The trench for underground fire service applications should be of ade-
quate width to allow convenient installation, while at the same time being
as narrow as possible. Minimum trench widths may be utilized by joining
pipe outside of the trench and lowering it into the trench after adequate
joint strength has been achieved.
Trench widths have to be wider where pipe is joined in the trench or
where thermal expansion and contraction is a factor. Refer to the “Snak-
ing/Deflection of Pipe” section on the following page.
• Water filled pipe should be buried at least 12 inches below the maximum
expected frost line.
• It is recommended that thermoplastic piping be run within a metal or
concrete casing when it is installed beneath surfaces that are subject to
heavy-weight or constant traffic, such as roadways and railroad tracks.
The trench bottom should be continuous, relatively smooth, and free of
rocks. Where ledge rock, hardpan, or boulders are encountered, it is
necessary to pad the trench bottom using a minimum of four inches of
tamped earth or sand beneath the pipe as a cushion and for protection of
the pipe from damage.
Sufficient cover must be maintained to keep external stress levels below
acceptable design stress. Reliability and safety of service is of major
importance in determining minimum cover. Local, state, and national
codes may also apply.
CAUTION
• Refer to the set and cure times listed in this manual for solvent cement joints.
Failure to follow these cure times before installing piping systems in trenches could
result in joint separation.
Pipe Size
Trench Width
inches
Light Traffic
Ground Cover
Minimum
inches
Heavy Traffic
Ground Cover
Minimum
inches
Nominal
Diameter
inches (mm)
Actual
Outside Dia.
inches (mm)
2 and under
2.375 and under
8
12 to 18
30 to 36
(50 and under)
(60,3 and under)
I-800 2755 Rev_I.fm Page 48 Tuesday, September 13, 2005 8:46 AM
