### **ITEM L-110 AIRPORT UNDERGROUND ELECTRICAL DUCT BANKS AND** **CONDUITS** {#item-l-110-airport-underground-electrical-duct-banks-and-conduits .Style-Heading-3Heading-3-CharHeading-3-Char1-CharHeading-3-Char-...}

DESCRIPTION

**110-1.1** This item shall consist of underground electrical conduits
and duct banks (single or multiple conduits encased in concrete)
installed in accordance with this specification at the locations and in
accordance with the dimensions, designs, and details shown on the plans.
This item shall include furnishing and installing of all underground
electrical duct banks and individual and multiple underground conduits.
It shall also include all turfing trenching, backfilling, removal, and
restoration of any paved or turfed areas; concrete encasement,
mandreling, pulling lines, duct markers, plugging of conduits, and the
testing of the installation as a completed system ready for installation
of cables in accordance with the plans and specifications. This item
shall also include furnishing and installing conduits and all
incidentals for providing positive drainage of the system. Verification
of existing ducts is incidental to the pay items provided in this
specification.

EQUIPMENT AND MATERIALS

**110-2.1 GENERAL.**

**a.** All equipment and materials covered by referenced specifications
shall be subject to acceptance through manufacturer\'s certification of
compliance with the applicable specification when so requested by the
Engineer.

**b.** Manufacturer\'s certifications shall not relieve the Contractor
of the Contractor's responsibility to provide materials in accordance
with these specifications and acceptable to the Engineer. Materials
supplied and/or installed that do not materially comply with these
specifications shall be removed, when directed by the Engineer and
replaced with materials, which do comply with these specifications, at
the sole cost of the Contractor.

**c.** All materials and equipment used to construct this item shall be
submitted to the Engineer for approval prior to ordering the equipment.
Submittals consisting of marked catalog sheets or shop drawings shall be
provided. Submittal data shall be presented in a clear, precise and
thorough manner. Original catalog sheets are preferred. Photocopies are
acceptable provided they are as good a quality as the original. Clearly
and boldly mark each copy to identify pertinent products or models
applicable to this project. Indicate all optional equipment and delete
non-pertinent data. Submittals for components of electrical equipment
and systems shall identify the equipment for which they apply on each
submittal sheet. Markings shall be boldly and clearly made with arrows
or circles (highlighting is not acceptable). Contractor is solely
responsible for delays in project accruing directly or indirectly from
late submissions or resubmissions of submittals.

**d.** The data submitted shall be sufficient, in the opinion of the
Engineer, to determine compliance with the plans and specifications.
\[The Contractor\'s submittals shall be neatly bound in a properly sized
3-ring binder, tabbed by specification section.\] The Engineer reserves
the right to reject any and all equipment, materials or procedures,
which, in the Engineer's opinion, does not meet the system design and
the standards and codes, specified herein.

**e.** All equipment and materials furnished and installed under this
section shall be guaranteed against defects in materials and workmanship
for a period of at least \[twelve (12) months\] from final acceptance by
the Owner. The defective materials and/or equipment shall be repaired or
replaced, at the Owner\'s discretion, with no additional cost to the
Owner.

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> **The engineer should specify the form in which submittals are to be
> received and number of copies.**
>
> **The length of time for guarantee of materials and workmanship should
> be as stated in the contract between the owner and contractor and the
> contract special provisions.**

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**110-2.2 STEEL CONDUIT**. Rigid galvanized steel conduit and fittings
shall be hot dipped galvanized inside and out and conform to the
requirements of Underwriters Laboratories Standard 6, 514B, and 1242.

**110-2.3 PLASTIC CONDUIT.** Plastic conduit and fittings-shall conform
to the requirements of Fed. Spec. W\--C-1094, Underwriters Laboratories
Standards UL-651 and Article 347 of the current National Electrical Code
shall be one of the following, as shown on the plans:

**a.** Type I--Schedule 40 PVC suitable for underground use either
direct-buried or encased in concrete.

**b.** Type II--Schedule 40 PVC suitable for either above ground or
underground use.

The type of adhesive shall be as recommended by the conduit/fitting
manufacturer.

**110-2.4 SPLIT CONDUIT**. Split conduit shall be pre-manufactured for
the intended purpose and shall be made of steel or plastic.

**110-2.5 CONDUIT SPACERS**. Conduit spacers shall be prefabricated
interlocking units manufactured for the intended purpose. They shall be
of double wall construction made of high grade, high density
polyethylene complete with interlocking cap and base pads, They shall be
designed to accept No. 4 reinforcing bars installed vertically.

**110-2.6 CONCRETE.** Concrete shall conform to Item P-610, Structural
Portland Cement Concrete, using **\[ \]** inch maximum size coarse
aggregate with a minimum 28 day compressive strength of **\[ \]** psi.
Where reinforced duct banks are specified, reinforcing steel shall
conform to ASTM A 615 Grade 60. Concrete and reinforcing steel are
incidental to the respective pay item of which they are a component
part.

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> **Typically, the maximum size aggregate should be speed as 1 inch,
> however, Engineer may specify smaller to accommodate special
> situations where 1 inch aggregate may he too large**
>
> **Item P-61 0 requires concrete to develop a 28 day compressive
> strength of 4, 000 psi. Engineer to determine the strength of concrete
> appropriate for the project and insert in paragraph 110-2.6.**

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**110-2.7 FLOWABLE BACKFILL.** Flowable material used to back fill
conduit and duct bank trenches shall conform to the requirements of Item
P-153 \"Controlled Low Strength Material\".

**110-2.8 DETECTABLE** WARNING **TAPE** Plastic, detectable, color as
noted magnetic tape shall be polyethylene film with a metallized foil
core and shall be 4-6 inches (75-150 MM) wide. Detectable tape is
incidental to the respective bid item.

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> **Specify color and legend.**

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CONSTRUCTION METHODS

**110-3.1 GENERAL**. The Contractor shall install underground duct banks
and conduits at the approximate locations indicated on the plans. The
Engineer shall indicate specific locations as the work progresses, if
required to differ from the plans. Duct banks and conduits shall be of
the size, material, and type indicated on the plans or specifications.
Where no size is indicated on the plans or in the specifications,
conduits shall be not less than 2 inches (50 mm) inside diameter or
comply with the National Electrical Code based on cable to be installed,
whichever is larger. All duct bank and conduit lines shall be laid so as
to grade toward access points and duct or conduit ends for drainage.
Unless shown otherwise on the plans, grades shall be at least 3 inches
(75 mm) per 100 feet (30 m). On runs where it is not practicable to
maintain the grade all one way, the duct bank and conduit lines shall be
graded from the center in both directions toward access points or
conduit ends, with a drain into the storm drainage system. Pockets or
traps where moisture may accumulate shall be avoided. No duct bank or
underground conduit shall be less than 18 inches below finished grade.
Where under pavement, the top of the duct bank shall not be less than 18
inches below the subgrade.

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> **For a closed conduit/duct bank system, the system should be designed
> to be connected to, and thus drain into, the airfield storm drainage
> system**
>
> **Engineer needs to be careful to define the term \"subgrade\" as it
> relates to pavement construction. In areas of pavement construction
> requiring the placement of embankment, or in areas requiring
> over-excavation to remove unsuitable material, the desired location of
> the top of the duct bank needs to be clearly identified In areas
> susceptible to frost, the top of the duct bank should be placed at or
> below the level of the frost line.**

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The Contractor shall mandrel each individual conduit whether the conduit
is direct-buried or part of a duct bank. An iron-shod mandrel, not more
than 1/4-inch (6 mm) smaller than the bore of the conduit shall be
pulled or pushed through each conduit. The mandrel shall have a leather
or rubber gasket slightly larger than the conduit hole.

The Contractor shall swab out all conduits/ducts and clean base can,
manhole, pull boxes, etc. interiors [IMMEDIATELY]{.underline} prior to
pulling cable. Once cleaned and swabbed the base cans, manhole, pull
boxes, etc. and all accessible points of entry to the duct/conduit
system shall be kept closed except when installing cables. Cleaning of
ducts, base cans, manholes, etc. is incidental to the pay item of the
item being cleaned. All raceway systems left open, after initial
cleaning, for any reason shall be recleaned at the Contractor's expense.
All accessible points shall be kept closed when not installing cable.
The Contractor shall verify existing ducts proposed for use in this
project as clear and open. The Contractor shall notify the Engineer of
any blockage in the existing ducts.

For pulling the permanent wiring, each individual conduit, whether the
conduit is direct-buried or part of a duct bank, shall be provided with
a 200 pound test polypropylene pull rope. The ends shall be secured and
sufficient length shall be left in access points to prevent it from
slipping back into the conduit. Where spare conduits are installed, as
indicated on the plans, the open ends shall be plugged with removable
tapered plugs, designed for this purpose.

All conduits shall be securely fastened in place during construction and
shall be plugged to prevent contaminate from entering the conduits. Any
conduit section having a defective joint shall not be installed. Ducts
shall be supported and spaced apart using approved spacers at intervals
not to exceed 5 feet.

Unless otherwise shown on the plans, concrete encased duct banks shall
be utilized when crossing under pavements expected to carry aircraft
loads.

Where turf is well established and the sod can be removed, it shall be
carefully stripped and properly stored.

Trenches for conduits and duct banks may be excavated manually or with
mechanical trenching equipment unless in pavement, in which case they
shall be excavated with mechanical trenching equipment. Walls of
trenches shall be essentially vertical so that a minimum of shoulder
surface is disturbed. Blades of graders shall not be used to excavate
the trench.

When rock is encountered, the rock shall be removed to a depth of at
least 3 inches below the required conduit or duct bank depth and it
shall be replaced with bedding material of earth or sand containing no
mineral aggregate particles that would be retained on a 1/4-inch sieve.
Flowable backfill may alternatively be used The Contractor shall
ascertain the type of soil or rock to be excavated before bidding. All
such rock removal shall be performed and paid for under Item P-152.

Underground electrical warning (caution) tape shall be installed in the
trench above all underground duct banks and conduits in unpaved areas.
Contractor shall submit a sample of the proposed warning tape for
approval by the Engineer. If not shown on the plans, the warning tape
shall be located six inches above the duct/conduit or the counterpoise
wire if present.

Joints in plastic conduit shall be prepared in accordance with the
manufacturer\'s recommendations for the particular type of conduit.
Plastic conduit shall be prepared by application of a plastic cleaner
and brushing a plastic solvent on the outside of the conduit ends and on
the inside of the couplings. The conduit fitting shall then be slipped
together with a quick one-quarter turn twist to set the joint tightly.
Where more than one conduit is placed in a single trench, or in duct
banks, joints in the conduit shall be staggered a minimum of 2 feet.

Changes in direction of runs exceeding 10 degrees, either vertical or
horizontal, shall be accomplished using manufactured sweep bends.

Whether or not specifically indicated on the drawings, where the soil
encountered at established duct bank grade is an unsuitable material, as
determined by the Engineer, the unsuitable material shall be removed in
accordance with Item P-152 and replaced with suitable material.
Alternatively, additional duct bank supports that are adequate and
stable shall be installed, as approved by the Engineer.

All excavation shall be unclassified and shall be considered incidental
to the respective L-110 pay item of which it is a component part.
Dewatering necessary for duct installation, erosion and turbidity
control, in accordance with Federal, State, and Local requirements is
incidental to its respective pay item as a part of Item L-110. The cost
of all excavation regardless of type of material encountered, shall be
included in the unit price bid for the L-110 Item.

Unless otherwise specified, excavated materials that are deemed by the
Engineer to be unsuitable for use in backfill or embankments shall be
removed and disposed of off site.

Any excess excavation shall be filled with suitable material approved by
the Engineer and compacted in accordance with item P-152.

It is the Contractor\'s responsibility to locate existing utilities
within the work area prior to excavation. Where existing active cables)
cross proposed installations, the Contractor shall insure that these
cable(s) are adequately protected. Where crossings are unavoidable, no
splices will be allowed in the existing cables, except as specified on
the plans. Installation of new cable where such crossings must occur
shall proceed as follows:

**(1)** Existing cables shall be located manually. Unearthed cables
shall be inspected to assure absolutely no damage has occurred

**(2)** Trenching, etc., in cable areas shall then proceed with approval
of the Engineer, with care taken to minimize possible damage or
disruption of existing cable, including careful backfilling in area of
cable.

In the event that any previously identified cable is damaged during the
course of construction, the Contractor shall be responsible for the
complete repair.

**110-3.2 DUCT BANKS**. Unless otherwise shown in the plans, duct banks
shall be installed so that the top of the concrete envelope is not less
than 18 inches (45 cm) below the bottom of the base or stabilized base
course layers where installed under runways, taxiways, aprons, or other
paved areas, and not less than 18 inches (45 cm) below finished grade
where installed in unpaved areas.

Unless otherwise shown on the plans, duct banks under paved areas shall
extend at least 3 feet (90 cm) beyond the edges of the pavement or 3
feet (90 cm) beyond any underdrains that may be installed alongside the
paved area. Trenches for duct banks shall be opened the complete length
before concrete is placed so that if any obstructions are encountered,
proper provisions can be made to avoid them. Unless otherwise shown on
the plans, all duct banks shall be placed on a layer of concrete not
less than 3 inches (75 mm) thick prior to its initial set. Where two or
more conduits in the duct bank are intended to carry conductors of
equivalent voltage insulation rating, the Contractor shall space the
conduits not less than 1-1/2 inches (37 mm) apart (measured from outside
wall to outside wall). Where two or more conduits in the duct bank are
intended to carry conductors of differing voltage insulation rating, the
Contractor shall space the conduits not less than 3 inches apart
(measured from outside wall to outside wall). All such multiple conduits
shall be placed using conduit spacers applicable to the type of conduit.
As the conduit laying progresses, concrete shall be placed around and on
top of the conduits not less than 3 inches (75 mm) thick unless
otherwise shown on the plans. End bells or couplings shall be installed
flush with the concrete encasement at access points.

Conduits forming the duct bank shall be installed using conduit spacers.
No. 4 reinforcing bars shall be driven vertically into the soil a
minimum of 6 inches to anchor the assembly into the earth prior to
placing the concrete encasement. For this purpose, the spacers shall be
fastened down with locking collars attached to the vertical bars.
Spacers shall be installed at 5 -foot intervals. Spacers shall be in the
proper sizes and configurations to fit the conduits. Locking collars and
spacers shall be submitted to the Engineer for review prior to use.

When specified, the Contractor shall reinforce the bottom side and top
of encasements with steel reinforcing mesh or fabric or other approved
metal reinforcement. When directed, the Contractor shall supply
additional supports where the ground is soft and boggy, where ducts
cross under roadways, or where shown on the plans. Under such
conditions, the complete duct structure shall be supported on reinforced
concrete footings, piers, or piles located at approximately 5 foot (150
cm) intervals.

All pavement surfaces that are to have ducts installed therein shall be
neatly saw cut to form a vertical face. All excavation shall be included
in the contract with price for the duct.

Install a plastic, detectable, color as noted, 4-6 inch (75-150mm) wide
tape 8 inches (200mm) minimum below grade above all underground conduit
or duct lines not installed under pavement.

When existing cables are to be placed in split duct, encased in
concrete, the cable shall be carefully located and exposed by hand
tools. Prior to being placed in duct, the Engineer shall be notified so
that he may inspect the cable and determine that it is in good
condition. Where required, split duct shall be installed as shown on the
drawings or as required by the Engineer.

**110-3.3 CONDUITS WITHOUT CONCRETE ENCASEMENT**. Trenches for
single-conduit lines shall be not less than 6 inches (150 mm) nor more
than 12 inches (300 mm) wide, and the trench for 2 or more conduits
installed at the same level shall be proportionately wider. Trench
bottoms for conduits without concrete encasement shall be made to
conform accurately to grade so as to provide uniform support for the
conduit along its entire length.

Unless otherwise shown on the plans, a layer of fine earth material, at
least 4 inches (100 mm) thick (loose measurement) shall be placed in the
bottom of the trench as bedding for the conduit. The bedding material
shall consist of soft dirt, sand or other fine fill, and it shall
contain no particles that would be retained on a 1/4-inch (6 mm) sieve.
The bedding material shall be tamped until firm. Flowable backfill may
alternatively used.

Unless otherwise shown on plans, conduits shall be installed so that the
tops of all conduits are at least 18 inches (45 cm) below the finished
grade.

When two or more individual conduits intended to carry conductors of
equivalent voltage insulation rating are installed in the same trench
without concrete encasement, they shall be spaced not less than 2 inches
(50 mm) apart (measured from outside wall to outside wall) in a
horizontal direction and not less than 6 inches (150 mm) apart in a
vertical direction. Where two or more individual conduits intended to
carry conductors of differing voltage insulation rating are installed in
the same trench without concrete encasement, they shall spaced not less
than 3 inches (75 mm) apart (measured from outside wall to outside wall)
in a horizontal direction and lot less than 6 inches (150 mm) apart in a
vertical direction.

Trenches shall be opened the complete length between normal termination
points before conduit is installed so that if any unforeseen
obstructions are encountered, proper provisions can be made to avoid
them.

Conduits shall be installed using conduit spacers. No. 4 reinforcing
bars shall be driven vertically into the soil a minimum of 6 inches to
anchor the assembly into the earth while backfilling. For this purpose,
the spacers shall be fastened down with locking collars attached to the
vertical bars. Spacers shall be installed at 5 -foot intervals. Spacers
shall be in the proper sizes and configurations to fit the conduits.
Locking collars and spacers shall be submitted to the Engineer for
review prior to use.

**110-3.4 MARKERS**. The location of each end and of each change of
direction of conduits and duct banks shall be marked by a concrete slab
marker 2 feet (60 cm) square and 4-6 inches (100-150 mm) thick extending
approximately 1 inch (25 mm) above the surface. The markers shall also
be located directly above the ends of all conduits or duct banks, except
where they terminate in a junction/access structure or building.

The Contractor shall impress the word "DUCT" or "CONDUIT" on each marker
slab. The Contractor shall also impress on the slab the number and size
of conduits beneath the marker along with all other necessary
information as determined by the Engineer. The letters shall be 4 inches
(100 mm) high and 3 inches (75 mm) wide with width of stroke 1/2-inch
(12 mm) and 1/4-inch (6 mm) deep or as large as the available space
permits. Furnishing and installation of duct markers is incidental to
the respective duct pay item.

**110-3.5 BACKFILLING FOR CONDUITS.** For conduits, 8 inches (200 cm) of
sand, soft earth, or other fine fill (loose measurement) shall be placed
around the conduits ducts and carefully tamped around and over them with
hand tampers. The remaining trench shall then be backfilled and
compacted in accordance with Item P-152 \"Excavation and Embankment\"
except that material used for back fill shall be select material not
larger than 4 inches in diameter.

Flowable backfill may alternatively be used

Trenches shall not contain pools of water during back, filling
operations.

The trench shall be completely backfilled and tamped level with the
adjacent surface: except that, where sod is to be placed over the
trench, the backfilling shall be stopped at a depth equal to the
thickness of the sod to be used, with proper allowance for settlement.

Any excess excavated material shall be removed and disposed of in
accordance with instructions issued by the Engineer.

**110-3.6 BACKFILLING** **FOR DUCT BANKS**. After the concrete has
cured, the remaining trench shall be backfilled and compacted in
accordance with Item P-152 "Excavation and Embankment" except that the
material used for backfill shall be select material not larger than 4
inches in diameter. In addition to the requirements of P-152, where duct
banks are installed under pavement, one moisture/density test per lift
shall be made for each 250 linear feet of duct bank or one work
period\'s construction, whichever is less.

Flowable backfill may alternatively be used

Trenches shall not contain pools of water during backfilling operations.

The trench shall be completely backfilled and tamped level with the
adjacent surface: except that, where sod is to be placed over the
trench, the backfilling shall be stopped at a depth equal to the
thickness of the sod to be used, with proper allowance for settlement.

Any excess excavated material shall be removed and disposed of in
accordance with instructions issued by the Engineer.

**110-3.7 RESTORATION**. Where sod has been removed, it shall be
replaced as soon as possible after the backfilling is completed. All
areas disturbed by the work shall be restored to its original condition.
The restoration shall include **\[sodding\]** **\[topsoiling\]
\[fertilizing\] \[liming\] \[seeding\] \[sprigging\] \[mulching\]**
shown on the plans. The Contractor shall be held responsible for
maintaining all disturbed surfaces and replacements until final
acceptance. All restoration shall be considered incidental to the
respective L-110 pay item.

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> **Engineer to specify the correct method of turfing and include in the
> construction documents the appropriate FAA turfing specification for
> restoration related to the installation of such duct banks and
> conduits.**

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METHOD OF MEASUREMENT

**110-4.1** Underground conduits and duct banks shall be measured by the
linear feet (meter) of conduits and duct banks installed, including
encasement, locator tape, trenching and backfill with designated,
resolution, and for drain lines, the termination at the drainage
structure, all measured in place, completed, and accepted. Separate
measurement shall be made for the various types and sizes.

BASIS OF PAYMENT

**110-5.1** Payment will be made at the contract unit price per linear
foot for each type and size of conduit and duct bank completed and
accepted, including trench and backfill with the designated material,
and, for drain lines, the termination at the drainage structure. This
price shall be full compensation for furnishing all materials and for
all preparation, assembly, and installation of these materials, and for
all labor, equipment, tools, and incidentals necessary to complete this
item in accordance with the provisions and intent of the plans and
specifications.

Payment will be made under:

> Item L-110-5.1 Electrical Duct Bank, **\[# and Size\]** ---per linear
> foot (meter)
>
> Item L-110-5,2 Electrical Conduit **\[# and size\]**---per linear foot
> (meter)

MATERIAL REQUIREMENTS

Fed.Spec.W-C-1094 Conduit and Conduit Fittings; Plastic, Rigid
(cancelled; replaced by UL 514 Boxes, Nonmetallic Outlet, Flush Device
Boxes, & Covers, and UL 651 Standard for Conduit & Hope Conduit, Type EB
& A Rigid PVC)

+---------------------------+------------------------------------------+
| > Underwriters            | Rigid Metal Conduit                      |
| > Laboratories Standard 6 |                                          |
+---------------------------+------------------------------------------+
| > Underwriters            | Fittings for Cable and Conduit           |
| > Laboratories Standard   |                                          |
| > 514B                    |                                          |
+---------------------------+------------------------------------------+
| > Underwriters            | Intermediate Metal Conduit               |
| > Laboratories Standard   |                                          |
| > 1242                    |                                          |
+---------------------------+------------------------------------------+
| > Underwriters            | Schedule 40 and 80 Rigid PVC Conduit     |
| > Laboratories Standard   | (for Direct Burial)                      |
| > 651                     |                                          |
+---------------------------+------------------------------------------+
| > Underwriters            | Type EB and A Rigid PVC Conduit and HDPE |
| > Laboratories Standard   | Conduit (for concrete encasement)        |
| > 651A                    |                                          |
+---------------------------+------------------------------------------+

**END OF ITEM L-110**