Minn-Dak Farmers Cooperative planned for a plant expansion in Wahpeton, North Dakota. The plant expansion project would include facilities to turn by-product sugar beet molasses into other products used in food, pharmaceuticals and feed supplements. Part of the expansion included the construction of a pipe bridge that was to be supported on concrete drilled shafts. The design of the pipe supports dictated that the drilled shafts have a diameter of 42 inches. Based on the engineer-of-record’s experience with deep foundations in the area, it was estimated that the foundationswould extend to an approximate depth of 35 feet to bear in competent glacial till. To provide a more economical foundation, the design team specified round shaft helical piles to be cast into and extended beyond the bottom of the 42-inch drilled shafts. This design allowed for a cost-effective combination system that would provide both vertical and lateral support to the structure.
The foundation design included 11 new construction helical piles with design working compression loads of either 20, 22, 26, or 55 kips per pile. The helical pile configurations consisted of five (5) Model 288 (2.875-inch OD by 0.276-inch wall) and six (6) Model 350 (3.50-inch OD by 0.313-inch wall) hollow round shafts with 10”-12”- 14” triple-helix lead sections. Prior to installing the helical piles, 42-inch diameter holes were augured to an approximate depth of 15 feet. Standard extensions were used to advance the piles to torque-correlated ultimate capacities of at least 40, 44, 52, and 110 kips (FOS ≥2). The piles were installed to an average depth of 35 feet. The tops of the piles were cut to the specified elevation and fitted with new construction brackets to be cast into the concrete drilled shafts. Despite facing many challenges associated with this unique installation, the installation of the 11 piles was completed in less than two days.
Structural Engineer: Sandman Consulting, PC
General Contractor: Key Contracting
Certified Pile Installer: Innovative Foundation Supportworks
Products Installed: (5) Foundation Supportworks® Model 288 Helical Piles and (6) Model 350 Helical Piles, 10”-12”-14” Lead Sections, Installed to an Average Depth of 35 feet, Design Working Loads of 20 to 55 kips