Structure 279 was located on an island, requiring alternative access methods and construction techniques. Drilled shaft foundations were planned for the other structures on the alignment, but would not be feasible for Structure 279 as the required equipment and materials for construction were too substantial for the location.
Crux was contracted by M.J. Electric to provide micropile foundation design-build services for the challenging H-frame structure. The equipment and materials needed for micropile installation can be compact and lightweight, offering a viable solution for locations such as this. The island was accessed by barge, and the drill was track-mounted to access the foundation site.
The island location also posed challenges to pouring concrete for concrete pile cap construction. To mitigate this, Crux introduced a unique steep pile cap design which could be manufactured offsite and transported to the structure location in one piece.
Geotechnical conditions featured approximately eight feet of loose soils over five feet of clay on top of weathered bedrock. Drilling of the first pile doubled as a geotechnical boring, allowing the design-build team to make minor refinements during installation and optimize the foundation to site specific conditions. Designs also had to factor in expansive river crossings on either side of the island, requiring substantial foundation capacity.