and match factory tapers. A coupling recommended by the duct manufacturer
shall be used whenever an existing duct is connected to a duct of different
material or shape. Ducts shall be stored to avoid warping and
deterioration with ends sufficiently plugged to prevent entry of any water
or solid substances. Ducts shall be thoroughly cleaned before being laid.
Plastic ducts shall be stored on a flat surface and protected from the
direct rays of the sun.
3.5.3
Concrete Encasement
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NOTE: For crossings of existing railroads and
airfield pavements greater than 15.2 m (50 feet) in
length, the pre-drilling method or the
jack-and-sleeve method will be used.
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Ducts requiring concrete encasements shall comply with NFPA 70, except that
electrical duct bank configurations for ducts 150 mm 6 inches in diameter
shall be determined by calculation and as shown on the drawings. The
separation between adjacent electric power and communication ducts shall
conform to IEEE C2. Duct line encasements shall be monolithic
construction. Where a connection is made to a previously poured
encasement, the new encasement shall be well bonded or doweled to the
existing encasement. The Contractor shall submit proposed bonding method
for approval in accordance with the detail drawing portion of paragraph
SUBMITTALS. At any point, except railroad and airfield crossings, tops of
concrete encasements shall be not less than the cover requirements listed
in NFPA 70. At railroad and airfield crossings, duct lines shall be
encased with concrete and reinforced as indicated to withstand specified
surface loadings. Tops of concrete encasements shall be not less than 1.5
m 5 feet below tops of rails or airfield paving unless otherwise indicated.
Where ducts are jacked under existing pavement, rigid steel conduit will
be installed because of its strength. To protect the corrosion-resistant
conduit coating, predrilling or installing conduit inside a larger iron
pipe sleeve (jack-and-sleeve) is required. For crossings of existing
railroads and airfield pavements greater than 15 m 50 feet in length, the
predrilling method or the jack-and-sleeve method will be used. Separators
or spacing blocks shall be made of steel, concrete, plastic, or a
combination of these materials placed not farther apart than 1.2 m 4 feet
on centers. Ducts shall be securely anchored to prevent movement during
the placement of concrete and joints shall be staggered at least 150 mm 6
inches vertically.
3.5.4
Nonencased Direct-Burial
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NOTE: Specify cover requirements in accordance with
NFPA 70 and IEEE C2. Specify frost line depth.
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Top of duct lines shall be below the frost line depth of [_____] mm inches,
but not less than [_____] mm inches below finished grade and shall be
installed with a minimum of 75 mm 3 inches of earth around each duct,
except that between adjacent electric power and communication ducts, 300 mm
12 inches of earth is required. Bottoms of trenches shall be graded toward
manholes or handholes and shall be smooth and free of stones, soft spots,
and sharp objects. Where bottoms of trenches comprise materials other than
sand, a 75 mm 3 inch layer of sand shall be laid first and compacted to
SECTION 16375A
Page 55
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