Foundation Supportworks of Wisconsin Case Studies: Helical Piles Installed for Northern Natural Gas Substation in Argyle, WI

Northern Natural Gas (NNG), headquartered in Omaha, NE, contacted Foundation Supportworks of WI (FSW) to stabilize a settled heater building at their substation near Argyle, WI. The substation is located on a property adjacent to low-lying wetlands. The lightly-loaded structure was originally supported on two horizontal “I” beams spanning the building’s width and set on top of 16-inch diameter concrete pilings.

Over the course of several years, two of the pilings on one end of the building settled ten inches. NNG was concerned that the settlementinduced stresses in the high pressure gas pipe lines could lead to failures in the lines or the connections.

NNG further requested that the building be lowered and leveled as close to the ground as possible to allow for easier entrance and exit.

Subsurface information was not available for this remote substation location. However, the piles were installed to torsional capacities of at least 2,250 ft-lb to provide a conservative design load of 10 kips/pile with a factor of safety of 2. Model 288 (2 7/8-inch OD x 0.276-inch wall) helical piles with an 8”-10”-12” lead section were advanced to depths of 19 to 21.5 feet. FSW first removed about 12 inches of frozen soil at the surface with a jack hammer in order to start the lead sections.

Care was taken during pile installation not to damage a photovoltaic solar panel and overhead gas lines. After all four piles were installed and elevations set, new “I” beams were placed on the pile caps. Floor jacks were used to lower the building onto the new beams. One side of the structure was lowered nine inches and the other side raised one inch to bring the building back to level.

A portable stick welder was used to weld the structure to the beams and the beams to the pile caps. The installation of the four helical piles was completed in one day.