Challenge

January 2011- An existing single family residence underwent a renovation project to the main and second floors of the structure. The home, located on the Gulf of Mexico, was originally constructed on driven concrete pilings. The renovation project would introduce additional loads to the concrete piles and also require installation of new piles for structural slab support. However, the limited access on the inside and outside of the structure would prevent the use of driven concrete piles. In addition, since the structure is located within a FEMA flood zone, the tops of new construction piles needed to be approximately 8 feet below existing grade due to scour depth requirements. Retrofit piles could be located at the elevations of the existing grade beams.

Solution

Retrofit helical piles were proposed to support the additional structural loads transferred to the existing grade beams. New construction helical piles would be installed to support the structural slab. The garage slab was removed and approximately 8 feet of soil was excavated to expose existing grade beams. The excavations were also extended to areas where new construction helical piles and grade beams would be installed. The retrofit helical pile configuration consisted of Model 288 (2.875-inch OD by 0.276-inch wall) round shaft with 10"-12" doublehelix lead sections to support a design working load of 7 tons. The new construction helical pile configuration consisted of Model 288 round shaft with 10"-12"-14" triple-helix lead sections to support a design working load of 15 tons. Helical piles were the ideal solution for this project because of the limited access within and adjacent to the residence. Thirty-one (31) retrofit and new construction helical piles were installed. Ultimate pile capacities, determined by correlation to installation torque, were at least two times the design working load (FOS ≥ 2). Even with the deep excavations and a high water table to contend with, the installation of the 31 helical piles took less than four days to complete and the project continued to move ahead on schedule.

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Project Summary

Architect:  Anthony J. Marszalec

Structural Engineer:  Cronin Engineering

Construction Manager:  Thomas Sebold & Associates

Certified Pile Installer:  N Square, Inc. dba Innovative Marine Construction Company

Products Installed: (31) Foundation Supportworks™ Model 288 Helical Piles, 10”-12” and 10”-12”-14” Lead Sections, Installed to depths of at least 42 feet, Design Working Loads of 7 tons and 15 tons