After mandrel-testing each conduit to confirm they were all clear of any obstructions or debris, a pulling head welded onto the front of the casing helped pull the entire length of the pipe string to the horizontal directional drilling exit pit, a distance of nearly 750 ft (229 m). The first line was ready to be attached to the Laney drill rig and pulled in.

Although Pearl Harbor's subsurface is comprised of dense shell sand with crushed coral and is generally favorable for directional drilling, this drill length is not exceptional for typical infrastructure installations. But, there were two principal complicating factors for this installation. First, Pearl Harbor is an active naval harbor, which meant ocean-going vessel traffic could affect the drill-head navigation system. Second, if the drill head veered too far off course, it could hit a recently installed 28-inch (711-mm) HDPE water line, which was a mere 20 ft (6 m) from the planned drill route. Any mistake would be costly.

In October, the directional drilling contractor Laney arrived in Honolulu with the drill rig and auxiliary equipment. Laney hired local divers to help install a TruTracker coil into the deeper water partially across the harbor to give the company more precise drilling control. Laney began drilling on Oct. 19, 2005. Eleven days later, the bit exited on the Ford Island side right on target. After completing two reaming passes and a swab run, the casing with the HDPE conduit bundle inside was ready to be pulled through. On Nov. 22, using a 750,000-lbs (340,194 kgs) class hydraulic drill rig, Laney pulled the 5025-ft (1532-m)-long north line underneath Pearl Harbor in a mere seven and a half hours.

The second drill was more complicated. Because there was now a newly installed, 24-inch carbon steel, highly magnetic casing 20 ft away, the TruTracker guidance system needed to be modified slightly. Laney contacted Tensteer, LLC (Georgetown, Texas) to help design a “Super Coil,” which had one leg running on the bridge and one inside the spare 6-inch conduit in the first casing. With this new guidance system, Laney began drilling the second pilot hole. On Dec. 4, the second bit exited on the Ford Island side and reaming could then begin. After several reaming and swabbing passes, Laney pulled in the second casing a few weeks later.

With both casings installed, AE took the project reins to prepare for the most precarious aspect of the project: pulling the solid dielectric cable through the conduit. A dielectric cable pull of this length is uncommon, so it naturally attracted a lot of attention.

Earlier in September, AE had brought in 12 reels of 46-kV XLPE cable. Each reel weighed 20 to 24 tons (18 to 22 metric tons) and carried 5300 ft (1615 m) of cable, just long enough to make it all the way under the harbor through the conduit. While HDCC assembled the HDPE conduit and casing, AE began pulling cable into PVC duct banks and installing the various riser and termination structures, starting first on the Oahu side and then working on the Ford Island side. The pulls through the duct bank averaged less than 60% to 80% of the calculated tension, the highest being around 3000 lbs (1361 kgs). The majority of the pulls were between 1400 lbs to 1800 lbs (635 to 816 kgs).

For the harbor pull, American Polywater assessed the tensile strength of the cable, the cable weight, the conduit fill percentage and the radii of the turns in the pull path, and determined a 0.17 coefficient of friction. It was time to put planning and calculations to the test. Because AE could not find a puller with enough pulling rope, AE had to get creative. Using a 20,000-lb (9072-kg) class Wagner-Smith TUDP-24 puller with a 0.625-inch (15.8-mm) wire rope, AE pulled approximately 1500 ft (457 m) of cable and then rerigged the pulling machine to pull in the remaining 3600 linear feet for each cable.

On the other end, AE devised a cable-feeding system consisting of a 5-ft (1.5-m) elephant trunk and a unique motorized roller system to control the curvature of the 46-kV cable bending radius to always be greater than the 60-inch (152-cm) minimum. Proper lubrication was critical for the cable-pulling process. AE used a SoaperMonkey (a lubricant application device) to prelubricate the conduits before the actual pulls. The goal was to ensure that no part of the cable was left unlubricated at any point during the pull.

The first set of cable pulls was completed in late January. AE took two days of preparation time and one day of pulling for each cable, averaging around 30 ft (9 m) per minute. The care taken during the planning stage proved critical. AE had calculated a ceiling tension of 12,000 lbs. Actual pull tensions turned out to be less than 7000 lbs (3175 kgs), with an occasional spike just above 8000 lbs (3629 kgs). The second set of cable pulls were completed a few weeks later.

After installation of the ground wire, fiber-optic cable and inner duct, the lines were spliced and grounded. In February, AE performed jacket integrity and 24-hour soak tests. On March 24, 2006, HECO energized the two new transmission circuits. A Navy dedication ceremony was held on May 23.

The 46-kV underground transmission project at Ford Island proved once again that any challenge can be overcome through teamwork and trust. HECO, HDCC, Laney, AE and others worked together in the spirit of cooperation to tackle this project's extraordinary challenges, which included everything from drilling under high-traffic waterways, pulling a mile of cable through conduit, and working in crowded conditions with multiple contractors near sensitive military facilities and historical sites. With the new 46-kV electrical feed, the U.S. Navy is one step closer to realizing a new Ford Island, one that provides a place everyone can enjoy and appreciate — and remember.

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Rodney Chong is a project manager for Hawaiian Electric Co. Inc., an investor-owned utility in Honolulu, Hawaii, U.S. Chong has a background in substation design and has been a project engineer and project manager for various T&D projects for 15 years. He holds a BSEE degree from the University of Hawaii and is a registered professional engineer and a certified PMP. rodney.chong@heco.com

Jerry Johnson is a senior project engineer for POWER Engineers. He has special expertise in underground transmission lines that includes: high-pressure pipe type systems, self-contained fluid-filled systems and extruded-dielectric systems from 69 kV through 400 kV. His cable installation experience includes trenchless technologies using horizontal boring and horizontal directional drilling. Johnson holds a BSEE degree from the South Dakota School of Mines and Technology, and he is a registered professional engineer. JJohnson@powereng.com