Crews recently wrapped up work on Minnesota Power’s Great Northern Transmission Line (GNTL), installing micropiles and grouted anchors in frozen ground and extreme temperatures. All work was successfully completed, with client Hooper/Wilson commenting “Crux did a good job of adjusting to unanticipated and ever-changing soil conditions. The knowledge and skill set they brought to the project was integral to the on-time successful completion of the foundation work.”
Helical piles were planned for all structures, but required an alternative at some locations after geotechnical investigations revealed shallow bedrock. Micropiles were selected as this alternative, and Crux installed a total of 22 micropiles and 28 grouted anchors to support 6 guyed foundations and 1 self-supporting lattice tower.
Micropile installation took place during the winter months, involving frozen ground conditions and working temperatures around -25°F. Located within wetland habitat, drilling also had to comply with strict environmental requirements, entailing cuttings removal and isolation of grout water to avoid contamination.
The GNTL is intended to deliver hydropower generated by Manitoba Hydro to customers in the United States. The line is expected to be in service by 2020.