Challenge

An elevated beach house built in 1949 was supported on timber pilings with wood cross bracing. Partial deterioration of the existing piles caused the one-story stilt home to settle up to 1.5 inches.

A geotechnical investigation was performed to explore the general soil conditions below the beach house. A single boring was performed to a depth of 25 feet below the existing grade and identified eight feet of loose to medium dense sand over medium dense to very loose sand to a depth of 22 feet. Three feet of weathered limestone was then observed to the bottom of the test boring at 25 feet. The groundwater table was encountered at a depth of six feet below grade at the boring location.

Preliminary repair options included either shoring the house to dig out the wooden piles and encase them in concrete, or worse, tearing down the structure and rebuilding on new pilings. The homeowners were desperate to find a more practical and economical solution to support the house.

Solution

The support solution had to be capable of being installed beneath the structure in limited access and low headroom conditions. Helical piles proved to be the ideal solution given the difficult installation conditions. The engineering staff at Foundation Supportworks® developed an adjustable top bracket detail for the piles to be placed concentrically beneath structural beams. The supplemental support system design included twenty-five (25) Model 350 (3.5-inch OD by 0.340-inch wall) round shaft helical piles with 10”-12” double-helix lead sections to support a design working load of 16 kips per pile. The helical piles were installed with handheld equipment to torque-correlated ultimate capacities of at least 32 kips (FOS ≥ 2). The pile sections and brackets were hot-dip galvanized for corrosion protection. The piles were installed and the beach house stabilized in four working days despite the difficult working conditions.

Print (PDF)

Project Summary

Structural Engineer: Kosinski Engineering, Inc.

Geotechnical Engineer: Forge Engineering, Inc.

Certified Pile Installer: N Square, Inc.

Products Installed: (25) Foundation Supportworks HP350 Helical Piles, 10"-12" Helix Plate Configuration, Custom Adjustable Bracket, Design Working Compression Load of 16 kips