Challenge

A beach (at grade) boardwalk was proposed at Gray’s Lake Park within the area between the Raccoon River and Gray’s Lake. The ADA compliant boardwalk would extend a slab-on-grade concrete trail to connect a parking lot with a playground located at the end of a small peninsula on the north side of the lake. A geotechnical investigation was not performed; however, marginal sand and clay soils were expected at the site. A cost-effective deep foundation system was required to resist frost heave and to provide support to the boardwalk if minor erosion of surficial soil occurs. In addition, construction of the boardwalk had to be completed within a limited time frame and with minimal disturbance to the park property.

Solution

The foundation design included ten (10) Model 287 (2.875-inch O.D. by 0.203-inch wall) round shaft helical piles with a 10”-12”-14” triple-helix lead section to support a specified design working load of 16 kips per pile. The helical piles were installed in two rows battered away from each other at an angle of 24 degrees from vertical. The piles were installed to depths from 22 to 32 feet below the ground surface and to torque-correlated ultimate capacities of at least twice the design working load (FOS ≥ 2). New construction brackets were attached to the tops of the helical piles and cast into concrete grade beams supporting the boardwalk. The pile leads, extensions and brackets were hot-dip galvanized per ASTM A123 to provide protection from corrosion. The pile installation was completed in one day.

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Project Summary

Structural Engineers: Gary Hlavka; Brateny Company

General Contractor: Joiner Construction

Certified Pile Installer: Foundation Supportworks® of Central Iowa

Products Installed: (10) Foundation Supportworks® HP287 Helical Piles, 10”-12”-14” Lead Section, Installed to Depths of 22 to 32 feet, Design Working Load of 16 kips