Current Design and Construction Practices For Micropile Supported Foundations

Current Design and Construction Practices For Micropile Supported Foundations of Electrical Transmission Structures in North America

Technical paper published by the International Society for Micropiles

This paper discusses innovative micropile foundation designs utilizing advanced steel and concrete caps constructed on several recent transmission projects. It details the foundation design selection process, 3D finite element simulation and design, steel cap testing procedures, construction challenges encountered, and specific benefits that foundation design provided to the projects.

Many of the construction sites detailed in the paper were located in remote, rugged terrain and required helicopter-only construction methods. At these sites, a design-build micropile foundation system was proposed and ultimately employed as an alternative to traditional concrete drilled shaft foundations. Typical micropile foundation construction included a circular array of battered micropiles installed to depths of approximately 35 feet at each tower leg or pole base. A concrete or steel pile cap was then selected to transfer the load from the stub angle to the micropile array.

These advancements in micropile foundation design and construction have been instrumental in the success of several large scale transmission projects in North America.