Crux provided 100% design-build services for four foundations located within the Cabot Substation, located in Montague, MA. This included foundations for two 155-foot-high monopoles as well as foundations for two 70-foot-high monopoles. Foundations for the taller poles consisted of 14 micropiles each, installed in a battered array and tied together with a buried concrete pile cap. Foundations for the 70-foot towers each consisted of 4 micropiles and a buried concrete cap.
Prior to drilling production micropiles, Crux completed a verification testing program. A non-production micropile was drilled and installed utilizing the same means and methods for the proposed structure micropiles. The grout to ground strength was then tested to 167% percent of the test load to ensure proper capacities had been met.
Once structure locations had been surveyed and cleared, micropile installation equipment was set in place either by forklift or mounted to track vehicles. SPT samples were taken during the drilling of the first pile at each foundation to determine the quantity of piles, length of piles and grouting method necessary for each individual structure. Drilling challenges included working in close proximity to many energized components in the substation. Additional challenges included encountering an unforeseen rock fracture, which consumed all contingency in the schedule.
Due to the drawdown date of an adjacent canal, all concrete pile cap construction had to be completed within a confined five day window. This included all excavation, installation of cap forms, rebar tying and concrete pouring. Crux mobilized additional resources to work on all caps concurrently and complete the project within the allotted schedule.