Micropile Foundations

Western Area Power Administration’s (WAPA) Gila-Welton Mohawk Transmission Line Interstate 8 Crossing involved upgrading 2.8 miles of aging infrastructure near Telegraph Pass in Southern Arizona.  11 of the wooden pole structures needing replacement were located in steep, challenging terrain, where conventional track equipment was unfeasible.  These structures required helicopter-supported construction methods.

Team Members


S.E. Incorporated

Crux Subsurface

Quanta Subsurface

Crux’s Role

Crux was selected to provide design-build micropile foundations for 8 steel poles that would replace the 11 wooden structures located in challenging terrain.  Crux’s specialized Berretta Spin Drills can be broken into lightweight components and allow for helicopter transport.  Micropiles were also an efficient solution to bridge through the hard rock found at these locations.  Crux installed groups of 3 to 6 micropiles in a battered array followed by installation of a steel pile cap.  In total, 44 micropiles were installed to between 24 and 32 feet.

In addition to the steep slopes, proximity to I-8 and a Marine Corps Air Station also created access challenges.  Three structures were located on an island bordered by I-8, requiring close coordination with the Arizona DOT.  Traffic restrictions were only allowed in one direction and resulted in two separate helicopter Landing Zones (LZ’s) to circumvent any flying over active roadways.  Construction plans and flight paths also had to factor in the potential traffic distraction, as multiple foundations were located directly adjacent to the roadway and in driver sightline.  In addition, several structures and one LZ were located within the Marine Corps Air Station’s restricted airspace, necessitating collaboration to approve flight paths and times.

All foundation work was successfully completed on time and with zero safety incidents.

Access challenges included steep, rocky slopes, and close proximity to both I-8 and a Marine Corps Air Station

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