October 12, 2017
The Koolau-Wailupe #1 and #2 46kV Structure Replacement project involved upgrading several wooden structures to self-supporting steel poles on the island of Oahu. The line had experienced numerous outages, and the upgrade was intended to increase reliability. Once complete, the Koolau-Wailupe segment will link to the Koolau-Poahakupu line, crossing through mountainous terrain from Honolulu to Waimanalo.
Hawaiian Electric Company, Road Bore Corporation, Crux Subsurface, Quanta Subsurface
The structures being replaced were located in extremely steep and rugged terrain, requiring helicopter-supported construction. Crux’s compact micropile drills matched well with project conditions, and steel cap micropile foundations were selected for 9 tubular steel poles. The equipment and materials required for micropile construction could be efficiently transported by helicopter, and the use of steel pile caps in place of concrete allowed for less onsite construction time. Crux’s specialty installation methods also enabled subsurface conditions to be efficiently characterized during construction, which was a key benefit to this project where conditions were unknown and proved to be challenging.
Brief outages were permitted during helicopter operations, but all drilling activities took place under in-service overhead lines. Adding to the challenges of setting equipment on steep slopes and between existing lines, crews were faced with extreme and unpredictable weather throughout the duration of the project. This included strong winds, rainstorms and heavy fog. To minimize schedule impacts, crews were prepared to move on and off foundation sites quickly during windows of opportunity. The use of steel pile caps allowed crews to take full advantage of these short windows, as they are fabricated offsite and set in one helicopter trip. Compared to concrete pile caps, the steel caps reduce helicopter use by an average 74% and onsite labor time by an average 64%.
During construction of the initial 9 foundations, Hawaiian Electric determined micropiles would be an efficient solution at 4 additional locations, and added to Crux’s scope. Crux provided an expedited design package for these foundations, successfully minimizing any schedule impacts.
Despite numerous challenges and risks, all foundation work was completed with no service interruptions to customers and zero safety incidents.