SECTION 26 11 50 – UNDERGROUND DUCTS, MANHOLES AND HANDHOLES
PART 1: GENERAL
1.01
1.02
DESCRIPTION:
A.
General provisions and other electrical systems are specified in other sections of Division 26.
B.
This Section covers underground ducts, manholes and handholes to form underground raceway systems
for power and signal conductors.
C.
Underground warning tape is specified in Section 26 00 10, General.
D.
Commissioning is specified in Section 26 00 90, Commissioning. This Section includes responsibilities
and obligations in support of the commissioning process specified therein.
QUALITY ASSURANCE:
A.
Conform to the following:
1.
ACI 318-2008.
2.
ASTM C478-2012.
3.
NECA/NEMA 605-2005.
4.
NFPA 70-2005.
PART 2: PRODUCTS
2.01
CONDUITS:
A.
2.02
As specified in Section 26 11 00, Raceways.
MANHOLES AND HANDHOLES - GENERAL:
A.
Shall be the size and shape indicated on the Drawings. Handholes shall be similar to manholes except
that cable racks are not required.
B.
Construction shall be reinforced concrete. Minimum concrete cover for reinforcing shall be 2" on exterior
surfaces, 1.5" for interior surfaces, and 1" for the bottom of the top slabs. Construct walls and floors
monolithically with window openings in walls for ductbanks.
C.
Shall be complete with:
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1.
36" diameter grooved circular opening for the installation of the frame and cover.
2.
Waterstops at framed cold joints.
3.
Frames and covers, of gray cast iron, machine finished with flat bearing surfaces. In roadways
and paved areas, frames and covers shall be traffic type; in unpaved areas, nontraffic type.
Covers shall be indented solid top design with two drop handles and the legend "Electrical" or
"Telephone", as appropriate, cast on the top side.
4.
Windows for initial and future duct line terminations.
5.
12" dry sump, 4" deep, with gray cast iron sump frame and cover at center and two 1" ground rod
openings in floor on opposite sides near the wall. Manhole floors shall be sloped 0.125" per foot
to sumps.
6.
Pulling irons in the walls opposite duct entrances approximately 6" above the top of each window.
Pulling irons shall be 0.875" diameter galvanized steel bars forming a triangle of 9" per side when
set.
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SECTION 26 11 50 – UNDERGROUND DUCTS, MANHOLES AND HANDHOLES
2.03
2.04
2.05
7.
Ground rods, copper-clad steel, 0.75", 10' long.
8.
Ground conductor, stranded bare copper #6 AWG minimum.
D.
Hardware and accessories shall be steel, galvanized after fabrication, except as otherwise specified
herein.
E.
Tops and walls of structures shall be designed for highway loading, with 30% additional for impact. Walls
shall be designed to withstand soil pressures, including ground water level, present at the site. Ground
water level shall be assumed to be 3' below ground surface unless a higher water table is determined at
the Project site.
MANHOLES AND HANDHOLES - PRECAST CONCRETE:
A.
Structures shall be precast monolithically or assembled in sections. Assembled sections shall have
tongue and groove mating edges with joints to interlock adjoining components, and waterproof junctions.
B.
Lifting devices shall be cast into the structures.
C.
Identify structures with the manufacturer's name embedded in, or otherwise permanently attached to, an
interior wall face.
CABLE RACKS:
A.
Heavy duty cable racks with adjustable arms, 36" on center minimum on walls. Arms shall be provided as
required for the cables, plus one additional spare on each rack channel.
B.
Inserts with minimum load rating of 800 lb to support cable rack channels.
C.
Cable rack channels, consisting of 4" x 1.5" x 0.188" steel channel wall brackets, 48" long, with arm
mounting slots 8" on center.
D.
Cable rack arms, of steel channel, 2.5" x 14" with high-glazed wet-process free moving porcelain saddle
insulators.
MISCELLANEOUS:
A.
Sealing devices: malleable iron, watertight, gland type with integral flanges and pressure bushings at each
end.
B.
Spacers: rigid, PVC type.
C.
Concrete: as specified in Section 26 00 10, General, except 28 day compressive strength shall be 4000
psig.
D.
Innerduct liners: corrugated high density orange polyethylene, with an inner diameter of 1".
PART 3: EXECUTION
3.01
GENERAL:
A.
Unless indicated otherwise on the Drawings, the following types of construction shall be used:
1.
Electrical service and circuits exceeding 5 kV or 800 A:
a.
2.
Telephone and data service:
a.
3.
Concrete-encased nonmetallic rigid conduit.
Electrical circuits other than those specified above:
a.
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Concrete-encased nonmetallic rigid conduit.
Rigid metal conduit without concrete encasement
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SECTION 26 11 50 – UNDERGROUND DUCTS, MANHOLES AND HANDHOLES
4.
Telephone and data conduits:
a.
5.
Manholes and handholes:
a.
3.02
Rigid metal conduit without concrete encasement.
Precast, or cast-in-place concrete.
B.
Excavation and backfill: as specified in Section 26 00 10, General.
C.
Concrete formwork, and reinforcing: shall conform to Division 03, Concrete.
DUCT LINE INSTALLATION - GENERAL:
A.
Slope ducts to drain towards manholes and handholes, and away from buildings and equipment
entrances. Minimum pitch shall be 4" per 100'. Where it is not possible to avoid a trap or low point in a
duct which is not concrete encased, provide a 0.5" hole drilled in the bottom of the conduit at the low point
and a crushed stone sump below the conduit. If possible, install the sump above the high water table
elevation. Otherwise prevent the accumulation of water within the conduit.
B.
Offset ducts to avoid conflicts with existing underground obstructions.
C.
Curved sections in duct lines shall consist of long sweep bends with a minimum radius of 50' in the
horizontal and vertical directions. Manufactured bends shall be limited to building entrances and stub-ups
to equipment.
D.
Underground conduit run to locations inside of buildings shall be rigid galvanized steel and shall extend a
minimum of 5' outside the building foundation. Stub-ups to equipment mounted on outdoor concrete slabs
shall be rigid galvanized steel and shall extend a minimum of 5' away from the edge of the slab. Install
insulated grounding bushings on the terminations of metallic conduit. Steel conduits shall be coupled to
the ducts with adapters, and the whole assembly encased with 3" of concrete.
E.
Keep ducts clean of dirt, sand, or gravel during construction, and sealed with tapered plugs upon
completion of each portion of the work.
F.
Upon completion of the duct line installation, pull a flexible mandrel through each conduit to loosen
particles of dirt, sand, or foreign material. Mandrels shall be not less than 12" long, and shall have a
diameter 0.5" less than the inside diameter of the conduit. A brush with stiff bristles slightly larger than the
conduit diameter shall then be pulled through each duct to remove the loosened particles.
G.
Seal ducts and conduits at building entrances, and at outdoor terminations for equipment, with a
nonhardening compound.
H.
Conduit extending up utility service poles shall be terminated in the manner required by the utility.
I.
Conduits shall be terminated in end bells, spaced approximately 9" on center at the face of manhole walls
for 4" conduits, and proportionately spaced for other sizes. The change from regular conduit spacing to
end bell spacing shall start 10' from the face of the manhole wall and shall be made in such a way that the
slope of any conduit shall not be less than that of the main bank and no trap will be formed.
J.
Joints in conduits and fittings shall be made watertight. Threaded portions of conduits that are not to be
encased in concrete, and adjoining ends of conduits, couplings and fittings, shall be heavily coated with
asphaltum after installation. Connections between conduits of different types shall be made using
adapters and methods recommended for the purpose by the conduit manufacturers.
K.
Where an underground conduit enters the building through a membrane-waterproofed wall or floor, a
sealing device shall be provided. Where a concrete envelope is required the sealing device shall be on
the inside only. Devices shall be securely anchored into masonry construction. Membrane waterproofing
shall be secured to the device in a permanently watertight manner.
L.
Conduits entering a building shall be sealed at the first termination with oakum or a plastic expansible
compound.
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SECTION 26 11 50 – UNDERGROUND DUCTS, MANHOLES AND HANDHOLES
3.03
M.
Where an underground conduit, not concrete encased, enters the building through a nonwaterproofed wall
or floor, provide a sleeve made of schedule 40 galvanized pipe. The space between the conduit and the
sleeve shall be filled with plastic expansible compound or an oakum and lead joint on each side of the wall
or floor. Sealing devices specified herein are acceptable in lieu of sleeves.
N.
Conduits shall be straight between manholes or upturned elbows. Where bends are unavoidable in
nonmetallic conduits, they may be made by assembling couplings at a slight angle, provided
the watertight seals are not broken and the resulting radius is not less than 100'. For radii less than 100',
5º angle couplings or 5º factory-made bend sections shall be used.
O.
Multiple conduit runs, direct burial or concrete encased, shall be supported on preformed, nonmetallic
separators. Spacing between exterior surfaces of conduits generally shall be not less than the following:
3" between conduits containing cables operating at similar voltage, and 6" between signal conduit and any
power conduit in the same envelope. Spacing between separators shall be close enough to prevent
sagging of conduits or breaking of couplings or watertight seals and to keep deformation of conduit at the
separators to 0.1" or less. Separators shall be secured with cords where necessary. No tie wires,
reinforcing rods or other metallic materials shall be placed in direct contact with conduits, either individually
or in groups.
P.
Multiple conduit runs shall be arranged substantially as indicated on the Drawings, but minor changes in
location or cross sectional arrangement shall be made as necessary to avoid obstructions. Where conduit
runs cannot be installed as shown because of conditions not discoverable prior to digging of trenches,
notify the Architect. Underground conduits shall be coordinated with other outside utility work. Existing
outside utilities shall be maintained in operation unless otherwise directed.
Q.
Where conduits cross under existing roadways, walks or other paved areas, rigid metallic conduits may be
driven under such areas in lieu of installing the conduits in trenches. After installation of conduit, existing
paved or grass areas which have been disturbed in any way shall be restored to their original condition.
Where the Drawings indicate spare conduits under existing roadways, walks, and other similar paved
areas, ends of conduits shall be capped 5' beyond the pavement. The ends of these conduits shall be
marked by the placement of 6" diameter by 18" long concrete monuments set flush in ground permanently
identified "Spare Conduit".
CONCRETE-ENCASED DUCTS:
A.
Spacers shall be installed maximum 5' on center, and shall support and maintain uniform spacing of the
duct assembly a minimum of 3" above bottom of the trench during the concrete pour.
B.
Extend the concrete envelope encasing the ducts at least 3" beyond the outside walls of the outer
conduits.
C.
Where new ducts, conduits, and concrete envelopes are to be joined to existing manholes, handholes,
ducts conduits, and concrete envelopes, make joints with fittings and fabricate the concrete envelopes to
ensure smooth transitions.
D.
Envelopes may be poured directly against the sides of the trenches if the cut is clean, even and free of
loose material. Forms are required where the soil is not self-supporting. Loose dirt and extraneous
material shall be removed from the trenches before and during pouring of concrete. Concrete shall be
carefully spaded during pouring to eliminate voids under and between the conduits and honeycombing of
the exterior surfaces. Power driven tampers or agitators shall be specifically designed for the application.
E.
Each run of envelope between manholes shall be poured in one continuous operation. Where more than
one pour is necessary, each pour shall terminate in a vertical plane, and 0.75" reinforcing rod dowels shall
be provided at each corner of the duct line and between exterior conduits, 1.5" from the exterior surface,
extending 18" into the concrete on each side of the joint.
F.
Where an envelope is installed over disturbed earth, across other conduits or pipe lines or under roads,
driveways, or parking areas, it shall be reinforced. Reinforcement shall also be provided where envelopes
connect to manhole and building walls.
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SECTION 26 11 50 – UNDERGROUND DUCTS, MANHOLES AND HANDHOLES
G.
H.
3.04
Within 10' of wall penetrations into buildings, manholes, and handholes, and within 10' of paved areas,
install No. 4 steel reinforcing bars. Reinforcement shall be located 1.5" in at each of the four corners of the
concrete envelope.
1.
In multiconduit ducts, additional intermediate reinforcing bars shall be located in a single layer
1.5" above the bottom of the concrete envelope. Locate intermediate reinforcing bars in the
center of each space between the conduits in the lowest row.
2.
In multiconduit ducts under paved areas, additional intermediate reinforcing bars shall be located
in a single layer 1.5" above the bottom of the concrete envelope and in a single layer 1.5" below
the top of the concrete envelope. Locate intermediate reinforcing bars in the center of each
space between the conduits in the lowest row and in the highest row.
The top surface of electrical ducts containing conductors of systems rated 300 V to ground or higher shall
be painted red for permanent duct bank identification.
MANHOLES AND HANDHOLES:
A.
Manholes and handholes shall not be constructed or installed until final conduit grading has been
determined, including field changes required by interferences with other underground utilities or structures.
B.
Where required due to depth below grade, provide a chimney with 30" minimum clear opening, consisting
of brick and mortar between the top of the manhole and manhole frame to reach the required level. Grout
the frame to the chimney.
C.
Install frames and covers flush with finished grade.
D.
Fill windows with concrete after installation of duct lines.
E.
Seal joints watertight, installing sealing material in strict accordance with the sealant manufacturer's
recommendations.
F.
Excavate below the sump 6" and fill sump bottom with clean gravel.
G.
Assembly and installation of precast components shall follow the recommendations of the manufacturer.
Precast units shall be installed on a level bed of well-tamped gravel or crushed stone.
H.
For cast-in-place structures, drive ground rods into the earth before the floor is placed, at a point close to
the manhole wall.
I.
For precast structures, drive ground rods into the earth through the floor sleeve after the manhole is set in
place. Fill the sleeve with sealant to make watertight.
J.
Ground rods shall protrude 4" above the floor.
K.
Install ground conductors around the inside perimeter and anchor them to the walls. Connect the ground
conductors to the ground rods by the exothermic welding process.
L.
Noncurrent-carrying metal parts including metallic sheaths of cables, equipment grounding conductors,
cable racks, steps, sump, frames and covers shall be connected to the ground rods by bare copper ground
conductors.
M.
Waterproof exterior surfaces, joints, and interruptions after concrete has cured 28 days minimum.
N.
Attach cable racks to inserts after construction is complete.
END OF SECTION 26 11 50
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