Leading Precast
Locke is a precast expert based in Houston, Dallas and the Gulf Coast area. We specialize in precast concrete, metal fabrication and the projects most people find too difficult. We’d love to help your business see the better side of building. Reach out today and we’ll be happy to help!
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Foundation Preparation
Precast concrete duct banks necessitate a stable, compacted foundation to ensure proper installation and long-term durability. Subgrade preparation must comply with project specifications, as well as any applicable geotechnical reports. Additionally, this preparation must ensure a stable, uniform foundation by properly compacting the soil to the specified density and addressing any potential issues such as soft spots, organic material, or excessive moisture.
Lifting Equipment Selection
Lifting equipment must be rated for the weight of the duct bank, or greater, to ensure both safety and the prevention of product damage. Undersized lifting gear presents substantial risk to both personnel and equipment. Proper lifting angles should be maintained to facilitate ease of alignment. The lifting configuration shown in the picture below is recommended to ensure optimal handling and placement.
Handling Duct Banks
Duct banks are designed with a minimum of four lifting points, depending on the size and weight of the units. Special care should be taken to prevent damage to the shear key or conduit spigots during handling. Should lubrication of gaskets be necessary, this should be performed on-site.
Alignment
Precise alignment of duct banks is essential to ensure a successful installation. This process should be carried out while the duct bank remains attached to the lifting equipment. As each duct bank is lowered into position, they should be carefully guided by hand into alignment with the mating duct bank (see picture below) and should be positioned with the spigot end inserted approximately ¼” into the bell of the mating section. Once aligned, they can be drawn into place using an excavator or similar machinery. Duct banks must be installed by pushing/pulling the spigot into the mating bell for optimal joint integrity. This can also be achieved by using a chameleon rigged to the adjacent duct bank’s lifting anchors.
Troubleshooting Alignment Issues
The following table provides solutions to common installation challenges:
| Issue | Solution |
|---|---|
| 1. Shear key prevents full conduit insertion. | Use the adjacent lifting lugs on the mating duct banks to incrementally lift each section until the shear keys align. Once aligned, carefully push the duct banks together. |
| 2. Soil or rock obstructs full conduit insertion. |
Lift the duct banks slightly using the adjacent lifting lugs to clear any soil accumulation between the ducts. After clearing, resume the insertion process. |
Integrating with Existing or Cast-in-Place Systems
Precast duct banks are engineered for seamless integration, whether as standalone systems or as extensions to existing installations. The duct banks are constructed using Schedule 40 PVC, rated for 90°C wire, which ensures compatibility with a wide range of system types.
Joining to Cast-in-Place Systems
Precast duct banks can be efficiently joined to cast-in-place systems through solvent-cementing the spigots of the duct bank to the corresponding conduit in the cast-in-place structure. The duct banks are manufactured with Schedule 40 Grey PVC, and the standard joining procedures for this material should be strictly followed. When connecting to the bell end of a duct bank, chamfer the ends of each conduit before insertion.
Joining to Precast Utility Vaults
Duct banks can also be designed to be integrated with precast utility vaults. The same joining methods outlined for cast-in-place systems apply, with shorter joining sections linking directly from the vault to the duct bank. A thin wall knock out will be casted into the vault and is required to be grouted in on-site to connect the duct bank and the vault.
Backfilling
Backfilling may proceed once the duct banks are securely placed and joined. The backfill material must comply with project specifications or any available geotechnical reports. In the absence of these documents, contractors are required to adhere to relevant state or local regulatory requirements for backfilling.
Choosing Precast for a Stronger, Safer Future
Precast concrete duct banks offer a reliable, efficient, and long-lasting solution for protecting vital utility lines and streamlining installation on the jobsite. By understanding their design, benefits, and proper installation methods, you can ensure safer, more durable infrastructure for your projects. Whether you’re planning a new build or upgrading existing utilities, choosing precast can help you save time, reduce risks, and deliver a higher-quality result.
To get an up-close look at a duct bank installation demo, you can check out our video below.
