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.
3.9.4
Nonencased Direct-Burial
**************************************************************************
NOTE: Specify cover requirements in accordance with
NFPA 70 and ANSI C2. Specify frost line depth.
**************************************************************************
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. Bottom 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
approximate densities of surrounding firm soil before installing ducts.
Joints in adjacent tiers of duct shall be vertically staggered at least 150
mm 6 inches. The first 150 mm 6 inch layer of backfill cover shall be sand
compacted as previously specified. The rest of the excavation shall be
backfilled and compacted in 75 to 150 mm 3 to 6 inch layers. Duct banks
may be held in alignment with earth. However, high tiered banks shall use
a wooden frame or equivalent form to hold ducts in alignment prior to
backfilling.
3.9.5
Installation of Couplings
Joints in each type of duct shall be made up in accordance with the
manufacturer's recommendation for the particular type of duct and coupling
selected and as approved. Duct joints shall be made by brushing a plastic
solvent on insides of plastic coupling fittings and on outsides of duct
ends. Each duct and fitting shall then be slipped together with a quick
1/4 turn to set the joint tightly.
3.9.6
Concrete
Concrete work shall be as specified in Section 03300A CAST-IN-PLACE
STRUCTURAL CONCRETE. Concrete shall be plain, 17 MPa 2500 psi at 28 days,
except that reinforced concrete shall be 21 MPa 3000 psi at 28 days. Duct
line encasement shall be of monolithic construction. Where a connection is
made to an existing duct line, the concrete encasement shall be well bonded
or doweled to the existing encasement.
3.9.7
Duct Line Markers
Duct line markers shall be provided [as indicated] [at the ends of long
duct line stubouts or for other duct locations that are indeterminate
because of duct curvature or terminations at completely below-grade
structures]. In addition to markers, a 0.127 mm (5 mil) 5 mil brightly
colored plastic tape, not less than 75 mm 3 inches in width and suitably
inscribed at not more than 3 m 10 feet on centers with a continuous
metallic backing and a corrosion-resistant 0.0254 mm (1 mil) 1 mil metallic
foil core to permit easy location of the duct line, shall be placed
approximately 300 mm 12 inches below finished grade levels of such lines.
SECTION 16528A
Page 37
Previous Page
