ELECTRICAL PRECAST DUCT BANK INSTALLATION GUIDE · PDF fileELECTRICAL PRECAST DUCT BANK...

ELECTRICAL PRECAST DUCT BANK

INSTALLATION GUIDE

This document details the foundation preparation, lifting equipment selection, handling of Duct Banks,

alignment, integrating duct banks into an existing or cast-in-place system, backfilling and tool checklist

for installation of Forterra Precast Electrical Duct Banks.

ELECTRICAL PRECAST DUCT BANK INSTALLATION GUIDE

Forterra Structural & Specialty Products 6655 Wedgwood Rd. N Suite 130 Maple Grove, MN 55311

Page 1

Matthew Pearson Technical Resource Engineer

[email protected] T:(763)-694-3256 M:(612)-807-4471

Contents Foundation Preparation ................................................................................................................................. 2

Lifting Equipment Selection ......................................................................................................................... 2

Handling Duct Banks .................................................................................................................................... 3

Alignment ..................................................................................................................................................... 4

Troubleshooting Alignment Issues ........................................................................................................... 5

Integrating Precast Duct Banks to an Existing or Cast-in-Place System ...................................................... 6

Joining Precast Duct Banks to a Cast-in-Place System ............................................................................ 6

Joining Precast Duct Banks to Precast Utility Vaults ............................................................................... 6

Backfilling..................................................................................................................................................... 7

Tool Checklist ............................................................................................................................................... 8



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Foundation Preparation Forterra Precast Electrical Duct Banks require a level, compacted foundation. Subgrade preparation will

be in accordance with project specifications and/or any available geotechnical report prepared for said

project. A smooth consumable organic material such as a Masonite board with minimum dimensions to

allow for roughly 18-24” of overlap on each side of the joint will be placed on the floor of the trench at

each joint location. The use of a ‘slide board’ will prevent rock and soil from interfering with the Duct

Bank joint and Shear Key. Figure 1 details the specifications of a typical slide board installation. Slide

Boards should be cleared of any soil prior to setting the next precast duct bank section. Any consumable

left within the trench should be approved by the project engineer prior to use.

Figure 1: Typical Masonite Board Placement

Lifting Equipment Selection Lifting equipment shall be rated for Duct Bank load or greater. Undersized equipment can be dangerous

and damage the product. Proper lifting angles will ensure easier alignment. Forterra recommends the

lifting configuration shown in Figure 2.



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Figure 2: Recommended Sling Angle (Minimum 60 Deg)

Handling Duct Banks Duct Banks will have either two or four lifting locations depending on the size and weight of the Duct

Bank. Care should be taken to avoid damage to Shear Key and conduit spigots. Conduit caps shall be left

in place until installation. If necessary, gaskets may need to be re-lubricated on-site prior to installation. A

visual inspection will determine if lubrication is needed. If the gasket does not have a glossy wet-like

appearance, then apply lubrication to the gasket.



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Alignment Duct Bank alignment is critical for successful installation. Alignment should occur while the Duct Bank

being installed is still attached to the lifting equipment. Each Duct Bank shall be lowered into place and

guided by hand to the mating Duct Bank Figure 3.

Figure 3: Hand Alignment

Pieces should be placed with the end of each spigot inserted roughly ¼” into the bell of the mating Duct

Bank. Once Duct Banks are aligned they can be pulled into place from the bell end using an excavator or

similar equipment. Duct banks MUST be installed by pulling/pushing the spigot into the mating bell.

Figure 4 details the correct procedure when pulling Duct Banks with an excavator or similar equipment.

An alternative method that may be used is the pulling sling cinch method shown in Figure 5. Using this

method, two adjoining duct banks are cinched together by a pulling sling attached to the forward and rear

lifting insert on the adjoining pieces.

Figure 4: Precast Duct Bank Pulling Procedure



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Figure 5: Cinch Method

Troubleshooting Alignment Issues

The following section details the most common installation issues and their solutions. Reference

the table below.

Issue Solution

Duct Bank Shear Key prevents full conduit

insertion.

Use the two adjacent lifting lugs on the mating

duct banks* and slowly lift each bank until the

shear keys are in alignment. Once shear keys

are aligned, push the duct banks together.

Issue Solution

Soil or rock has built up between the ducts and

prevents full conduit insertion.

Duct banks cannot be pulled apart once the

spigot engages the grip ring. Using the two

adjacent lifting lugs on the mating pieces*, lift

the pieces enough to clear the soil collection

trench. Once cleared try the push again.

Depending on soil type, soil collection trenches

may need to be oversized.

*See Figure 6 for shear key alignment lifting configuration.



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Figure 6: Shear Key Alignment Lifting Configuration

Integrating Precast Duct Banks to an Existing or Cast-in-Place System

Forterra Precast Electrical Duct Banks are designed to function as an entire system, or as an addition to a

larger system. The Duct Banks utilize standard Schedule 40 PVC rated for 90C wire to ensure seamless

integration into any Duct Bank system.

Joining Precast Duct Banks to a Cast-in-Place System

Forterra Precast Electrical Duct Banks can be joined to an existing or cast in place system with

ease. Simply solvent cement the spigots of the mating Forterra Duct Bank conduit to conduit in a

cast-in-place system. Forterra Duct Banks use Schedule 40 Grey PVC and all applicable

standards and procedures for joining Schedule 40 Grey PVC apply. If joining to the bell end of a

Forterra Duct Bank, chamfer the ends of each conduit prior to inserting into each bell. For 4”

diameter conduit, mark 6” from the mating end of the conduit. For 6” diameter conduit, mark 7”

from the mating end of the conduit. 70lbs of insertion force is required for the conduit to seat

correctly. Use a wooden block and mallet to insert the joining conduit to the marked location.

Joining Precast Duct Banks to Precast Utility Vaults

Forterra Duct Banks can also be joined to Precast Utility Vaults. Using the methods described in

the previous section, shorter joining sections can be installed directly from the Utility Vault to the

Duct Bank. This requires only a small section of Cast-in-Place conduit to be placed at the end of

each line Figure 7.



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Figure 7: Joining Precast Duct Banks to Precast Utility Vaults

Backfilling

Backfilling can begin as soon as Duct Banks are placed and joined. Fill will be in accordance with project

specifications and/or any available geotechnical report prepared for said project. In absence of either of

these two, contractor shall refer to applicable state requirements.



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Tool Checklist

□ Long Reach Trowel

□ 2 pry bars

□ 48” Level

□ Transit Level

□ Mallet

□ 1’ Section of 2x4

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