Hawaiian Electric commissioned the replacement of several structures along the Koolau-Wailupe # 1 & #2 46 kV Circuits line on the island of Oahu. The project featured difficult access, with steep, rugged terrain and unpredictable weather patterns, and included the additional challenge of working under existing overhead lines.
Quanta Subsurface (QS) was selected to provide a design-build foundation solution at nine 46 kV self-supporting steel pole structures. Collaborating closely with contractor Crux Subsurface (Crux) to incorporate the company’s specific means and methods allowed for optimized designs. Steel cap micropile foundations were selected to accommodate helicopter-supported operations and short construction windows due to inclement weather. Crux’s specialty helicopter-portable equipment and the compact materials required for micropile construction were ideal for project conditions. Additionally, the steel pile caps could be fabricated offsite and flown onto installed piles quickly and efficiently.
During construction, the owner determined micropiles would be an efficient solution at four additional structure locations. These four foundations were added to Crux’s scope and an expedited design package was requested. QS successfully performed and submitted the requested designs in less than five days.
The presence of saprolites and transition rock in subsurface materials created additional design challenges. Saprolites are complex materials that behave as a soil in engineering terms, but may still exhibit some rock properties. Precise identification of saprolite zones is integral to micropile design and the successful performance of the foundation. Onsite monitoring allowed QS to accurately identify areas of concern, and all thirteen foundations were installed successfully and economically.