Design-Build F-16 Aggressor Squadron Operations Electrical Infrastructure, Nellis AFB, NV - W912PL-10-C-0022
Customer/Owner Name U.S. Army Corps of Engineers
Point of Contact: Rodolfo Posis
Description: The purpose of this project was to take 17,100 SF of existing above-ground high-wire and place it underground. The scope of work required all of the electric work including, but not limited to: excavation, electrical wiring, necessary power supply, telephone communications cables, conduit and terminations; fiber optic cable, conduits and terminations, data distribution system and fire alarm systems within an F-16 Aggressor Squadron Operations Facility. Additional work included providing design, potholing, electrical duct banks, trenching, concrete, wire and backfill, demolition, survey, restoration of landscape and hardscape, precast concrete repairs, switchgears and testing.
This project is a Design-Build for five (5) different locations of Nellis Air Force Base in North Las Vegas, Nevada. The goal of this project is to modify and/or add to the existing electrical primary service and to increase the reliability of Nellis AFB’s electrical distribution system. The following is a description of work typical to the five different tasks.
The tasks, although on different parts of the base, followed the same general plan. The five locations either had an existing overhead distribution system, or none at all. Our goal was to install a reliable underground system and in some cases eliminate the overhead less reliable and dated overhead system. The five (5) tasks ranged from 250 FT to 6700FT. The tie-in points to the new underground system were either into an existing overhead system, in which we would continue our underground system up a power pole through a pole riser conduit and allow for future expansion, or a piece of switchgear like a 4-Way Switch. Seventeen new switches were added to the system to increase reliability and redundancy.
The first step in installing the new system was to establish the locations of the various pull boxes and switch boxes. The pull boxes were concrete pre-cast box assemblies that had a steel lid that opens and closes are generally located in areas where a change in direction is required, so as to not create excessive stress on the conductors when they are being pulled through the conduit, and are spaced out about every 500 FT per general industry standards. When a pull box was used in a change of direction, it served as a location where the conductors were spliced together, otherwise, excessive friction could occur on the conductors while they were being pulled through the conduit. Switch boxes were also pre-cast concrete boxes, on this project the pull boxes and switch boxes were identical, but the switch boxes were sealed off with a 1 FT thick precast concrete slab with inserts to support the switches, in lieu of the steel lid.
After the locations of the boxes were established, the area is excavated to allow for installation. Type II backfill is compacted to 95% on the bottom of the excavation and is made level, and the boxes were installed. After which, a trench was excavated from box to box. For this project, we installed two (2) 6-IN conduits, one (1) for the conductors and one (1) as a spare for future expansion. The specifications require 36-IN of cover over the conduit and 12-IN of concrete embedment, so a 4-FT deep by 2-FT wide trench was dug using a backhoe with a 2-FT bucket. Spacers were installed under the conduit to allow the concrete to settle on all sides of the conduit. After the conduit was installed and concrete allowed to cure to 2000 PSI, the trench was backfilled in two (2) 18-IN lifts compacted to 90% relative compaction.
With all the conduit and pull boxes in-place, the conductors were pulled through. The first step in pulling the wire was to blow a nylon rope through the conduit from one box to the next. Plastic sheeting was attached to the nylon rope and the rope was blown through one (1) pull box with an air compressor until it reached the next pull box in line. After the nylon rope was installed, it was tied to ¾ -IN pulling tape with a 2500 LB tensile capacity and the nylon tape was pulled out so the mule tape now took its place within the conduit. After which, the mule tape was tied onto the ¾-IN aircraft cable and the mule tape was pulled through the conduit so the aircraft cable was within the conduit. With the heavy duty aircraft cable in-place, the three (3) phases of cable were pulled through the conduit using a wench system.
With the cable in-place, the splicing can occur within the pull boxes. Splice kits allowed the two (2) conductors to be fused together, keeping voltage, amperage, and insulation consistent through the two sections of cable. At points of termination (i.e. locations where the conductor land in a switch), a load-break elbow was installed on the end and the conductors were tied together to allow for testing. This tee arrangement can easily be disassembled to operate the conductors inside the switch.
Three (3) items were tested: the switches, the conductors, and the transformers. After the three (3) items are tested and approved, the system can be energized. A portion of the existing system was de-energized for a day to allow the new system to be tied-in via splicing and inspection by the base electricians, after approval of the splicing, the system was re-energized and the new system became ready for use.
Award Amount: $5,618,000