Twin City Hardware

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Project Location

Twin-City Hardware
New Hope, Minnesota
November 2009

Helical Piles and Floor-slab Piers

Helical Piers

An addition was constructed at the existing Twin-City Hardware building in New Hope, Minnesota. The 100’x220’ concrete addition was to include both warehouse and office space. Beneath the new addition, geotechnical borings indicated up to 20 feet of very soft swamp-deposited peat and organic silt overlying stiff sandy clay glacial till soils. Wall loads were estimated to be on the order of 7 to 11 kips per lineal foot and column loads were estimated to be 90 kips.

Prior to building construction, it appears that earthwork operations included a partial over-excavation and replacement of the unsuitable organic soils. 

Helical Piers

It is understood that the building started to settle and construction crews re-leveled the walls multiple times during construction. Within a few years of completion, portions of the building had experienced an additional 6 inches of settlement. 

Our dealer was awarded the project and was to install 93 helical piles and 39 floor slap piers to support the distressed areas of the building. The helical piles were installed alternating inside and outside under the east foundation wall and were installed from the outside along the south exterior foundation wall.

Helical Piers

Due to the heavy foundation loads, the project included installing Grip-Tite’s Heavy Duty Retrofit Brackets and utilizing lead sections with 10”, 12” and 14” helices on all of the helical piles. Galvanized material was selected due to the presence of high groundwater levels and organic soils. The helical piles were installed to ultimate capacities on the order of 76 kips and terminated within the glacial till soils near depths of 30 to 55 feet below bottom of footings.

Helical Piers

Preparing the footings included core-drilling through 18 to 24 inch thick footings in order to place the retrofit bracket beneath the foundation walls. In addition, installing the floor-slab piers included working in limited space around office desks, interior walls and built-in drafting tables.

The building was lifted to near vertical all at once, which took a huge effort by the Grip-Tite team.

American Engineering Testing, Inc. provided continuous observation and testing throughout the entire project.