Challenge

An equipment addition was planned within a three-story, steel foundry building. The equipment would be supported on four columns with an estimated service load of 200 kips per column. A geotechnical investigation performed in the area of the proposed equipment identified weak sand and clay layers over medium dense sand and hard glacial till. The competent bearing strata was encountered at a depth of 52 feet below the existing floor slab elevation. Deep foundations were therefore proposed to support the interior column loads. The deep foundations would have to be installed quickly while the foundry was temporarily shut down.

Solution

Helical piles were selected over other deep foundation types for the proposed interior installation. Helical piles can be installed quickly using relatively small equipment within limited working space. The foundation design included four helical piles at each column location. The helical pile configuration consisted of Model 350 (3.500-inch OD by 0.313-inch wall) hollow round shaft with a 10”-12”-14” triple-helix lead section followed by a 14”-14” extension to support a design working load of 50 kips. Standard extensions then advanced the piles to depths from 63 to 75 feet below floor slab elevation to bear within the competent sand and till. The piles were advanced to torquecorrelated ultimate capacities of at least twice the design working load (FOS ≥ 2). The piles were fitted with standard new construction brackets and cast into concrete pile caps. The helical pile installation was completed within four days.

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Project Summary

Architect/Structural Engineer: Townsend Engineering

Geotechnical Engineer:: TEAM Services, Inc.

General Contractor: General Constructors, Inc.

Certified Pile Installer: MidAmerica Basement Systems

Products Installed: (16) Foundation Supportworks® HP350 Helical Piles, 10"-12"-14"-14"-14" Plate Configuration, Installed Depths from 63 to 75 feet Below Floor Slab Elevation, Design Working Load of 50 kips