Model 288/350 Helical Piles - Lion and Baboon Exhibit
Knoxville Zoo, Knoxville, Tennessee

Challenge:

Test boring.

The proposed site for the new Knoxville Zoo Lion and Baboon Exhibit was within a previously developed area of the property.

The six test borings completed for the project encountered undocumented fill to depths ranging from 11 to 17 feet.

The fill was primarily described as silty clay with rock fragments, although isolated pieces of debris and trash were also observed.

Standard penetration test blow counts (N-values)within the fill ranged from 2 to 14 blows per foot. The fill is underlain byresidual silty clay and bedrock.

The test borings refused on apparent limestonelayers at depths of
11 to 23.5 feet.

Advancing helical piles.

The geotechnical engineer recommended that the exhibit be supported by deep foundations extending down to the bedrock surface.

Design working loads for the 56 piles ranged from 20 to 70 kips, but were mostly in the range of 20 to 50 kips.

Solution:

Helical pile foundations were selected to extend through the fill and native residual soils for bearing on or within the limestone bedrock.

The piles would likely "spin-off" on top of the hard bedrock surface rather than cut into the material with the helix blades and develop a torque to capacity correlation.

New construction bracket of helical pile in grade beam.

The allowable mechanicalcapacity of the pile shaft was therefore considered in the pile selection.

The foundation design included 37 Model 288 (2.875-inch O.D. by 0.276-inch wall) and 19 Model 350 (3.5-inch O.D. by 0.313-inch wall) round shaft helical piles.

All piles had an 8”-10” double-helix lead section with the 8-inch blade being ½-inch thick and special order V-style cut. The beveled tips of the lead sections were cut off straight to allow for better end bearing of the shaft on the bedrock surface.

The 56 piles were installed to depths ranging from 8 to 33 feet. The pile installation was completed in three days.

Architect: Johnson Architecture

Placement of reinforcing steel.

Structural Engineers: Robert H. Houser and Hayman Foundation Engineering, LLC

Geotechnical Engineers: Engineering & Testing Solutions, LLC

General Contractor: Merit Construction

Certified Tieback/Anchor Installer: American Foundation & Basement Repairs, LLC

Products Installed: (37) Foundation Supportworks™ Model 288 Helical Piles and (19) Foundation Supportworks™ Model 350 Helical Piles, 8"-10" Lead Section, Installed to Depths of 8 to 33 feet, 20 to 70 kip Design Working Loads

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