Steep Slope Micropile Installation
ITC Midwest commissioned the refurbishment of an existing 161 kV transmission line. The 50-mile Lansing to Harmony alignment runs through northeast Iowa and southeast Minnesota, traversing rolling hills and a number of private properties. The refurbishment entailed the replacement of approximately 120 wood “H” frame structures with steel “H” frame structures.
L.E. Myers Company
Crux was selected to provide 100% design-build foundation services for one steel “H” frame structure and an adjacent 60-foot by 30-foot steel maintenance platform. Both structures were located on a 45 degree slope and required helicopter transport for all materials, equipment and personnel. Site-specific geotechnical data was not available for these structures because of the challenging location, leading to the selection of micropile foundations. Micropiles can readily adapt to variable subsurface conditions and are well suited for helicopter transport.
Nineteen piles were installed for the steel platform and six were installed to support the structure. Subsurface conditions consisted mostly of limestone, although challenges arose when a fault was encountered. The void in materials required an increased amount of grout to achieve capacity. Crux crews adapted the pile design onsite and successfully installed all twenty-five piles to the desired capacity.
Additional project challenges included adequately setting up drill platforms on the steep terrain. Weather was also a factor, as wet, soft ground conditions increased access restraints. Initial project plans called for workers to drive to within a certain proximity of the site and hike from the tree line. Rain caused these roads to be unusable, and workers were required to utilize helicopter transport to access the drill site.