Crux provided micropile design-build services for 11 tubular steel poles and one lattice structure on Segment 16DCT. Micropiles were selected as a deep foundation alternative at these locations due to high groundwater and the need to minimize the disturbance area of foundation construction activities on private, organic lands.
Steel pile caps were designed for 7 monopole foundations and the lattice structure. The caps were fabricated offsite in a controlled environment, allowing for decreased onsite construction times and higher overall quality assurance. The remaining 4 monopoles were deadend structures with higher groundline reactions. Steel caps for foundations this size became uneconomical, and 29-foot-diameter concrete caps were constructed at these locations.
Matted roadways were placed, and additional onsite measures were taken to control spoils and avoid contamination of the surrounding area. At steel cap locations, the client provided what became known as a “bathtub” setup. Mats were set around the foundation location and the center was excavated approximately one foot. The basin was draped with plastic tarp to contain drill fluid and cuttings. At concrete cap locations, Crux fabricated a closed cell cofferdam and placed a rotating drill carriage on top. This effectively served as a drill platform during installation, contained fluid and cuttings, and acted as a form for concrete cap construction.
Additional project challenges included working below energized lines to remain on schedule, deep mud rotary drilling, and working within tidal-affected areas. In total, 112 micropiles were installed to depths between 30 and 165 feet.