Challenge

A two-story building addition with a partial basement was planned at the existing Tyson Foods facility. The addition had approximate plan dimensions of 60 feet by 90 feet. Construction details included steel framing and precast concrete panels with wall loads on the order of 8 kips per linear foot. The project area was surrounded by existing structures to the north, east and south and a railroad spur to the west. The processing plant is located within the alluvial plane of the Missouri River. Sub-surface conditions at the site were determined with four test borings completed to depths ranging from 20 to 70 feet. Groundwater was encountered at depths ranging from 35 to 40 feet. A generalized subsurface profile consists of fill soils over weak clays and silts over loose to dense sand to the bottoms of the borings. The fill varied from clay to sand to crushed gravel and extended to depths of 7 to 15 feet below the surface. The weak alluvial clays and silts extended to depths of 30 to 35 feet.

Solution

The design team considered options of over-excavation with soil replacement, auger-cast piles and helical piles to provide support for the new addition. The over-excavation and backfill option was quickly dismissed due to the depth of excavation necessary and the risk of undermining existing foundations. Limited access to and within the project area, as well as overhead obstacles including power lines, piping and conveyor systems would hinder installation of auger-cast piles. Helical piles were selected as the ideal foundation support option given the smaller installation equipment required. This equipment could easily maneuver within the limited area and also below or around the overhead obstacles. The foundation design included 89 Foundation Supportworks® Model 288 helical piles. The pile configuration consisted of 2.875-inch OD by 0.276-inch wall hollow round shaft with 10”-12”-14” triple-helix lead sections. Due to soil variability across the site, 14”-14” double-helix extensions were added to minimize installation depths. The piles were installed to depths ranging from 33 to 65 feet, with an average depth of 53 feet. Ultimate pile capacities determined by correlation to installation torque, were at least 80 kips (FOS ≥ 2). A site-specific torque correlation factor was utilized based on contractor experience in the area.

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Project Summary

Structural Engineer: Schneider Structural Engineering

Geotechnical Engineer: Certified Testing Services, Inc.

General Contractor: HCI Construction

Certified Pile Installer: Foundation Supportworks by Thrasher

Products Installed: (89) Foundation Supportworks® Model 288 Helical Piles, 10”-12”-14” Lead Section and 14”-14” Extension, Installed to an Average Depth of 53 feet, 40 kip Design Working Load