Micropiles for Support of Heavy Crane Ring Foundation

The replacement of a steam generator at a nuclear power plant was accomplished with the use of a massive crane, believed to be one of the largest available cranes in the world market. Four steam generators were replaced, with each generator weighing 3.2 MN. The crane used for the job had a circular support that required a ring foundation. The crane support imposed huge loads on the ring foundation. Because of the presence of soft to medium stiff clayey fill on one side of the ring foundation, the load-sensitive nature of existing underground safetyrelated duct banks, and the nature of the loads applied to the foundation, it was necessary to support the ring foundation on piles. In order to minimize vibrations next to the containment building (the plant was operational while the piles were being installed), micropiles were selected. A total of 80 micropiles were installed, most of them at a batter of 10o from vertical, to provide the required vertical and lateral load resistance. Despite significant challenges imposed by space constraints, subsurface conditions, buried utilities, and design changes, the micropiles were installed within schedule, and performed as designed