Coastal Foundation Solutions were retained by Benton & Sons Construction Company, a specialist marine construction division, for the design and installation of a permanent helical pile anchor system. The primary concerns of the design and engineering team were the design life of the structure in a marine environment and the structural capacity of “Chance” helical tieback anchors under loadings of up to 24,000 pounds (12 tons) in tension.
The Coastal Foundation Solutions engineering and design team visited the site to confirm the scope of works and discuss the design process with the Project Manager. Since the original construction design had concrete deadman and reinforcing steel tie-backs, the driven helical anchors would need to be set to avoid clashing with the existing structures and large oak trees.
The structural engineer overseeing the design of the seawall replacement project provided Coastal Foundation Solutions with the seawall loadings and the revised layout of the helical anchor locations. This information came with the soil report of the location, which determined the helical system to employ. Furnished with this latest information, the Foundation Technologies engineering team proceeded with the design and recommendations for the project.
HELICAL PILE INSTALLATION
Before the installation of production piles, the General Contractor, Benton and Sons, pre-excavated pile locations to eliminate potential obstacles. Pre-excavation proved to be worthwhile, as all 35 piles were successfully installed at their planned locations. Upon termination, all helical piles were cut to their required elevation. All helical piles were rotated into position in 3 days, which included mobilization. Pile production included a full-time Quality Control person to oversee pile testing and installation. Pile monitoring was performed by Hans Wilson and Associates of Fort Myers, Florida. The helical piles were installed by Coastal Foundation Solutions (CFS), a Certified Installer of “CHANCE” Helical Foundations Systems. As Coastal Foundation Solutions was appointed to conclude the tie-back installation, special precautions were taken for efforts to take place in a marine environment. All elements of the installation components were hot dipped galvanized.
Thirty-five (35) CHANCE SS150 (1.5-inch square bar) helical tiebacks with a 10”-12” double-helix lead section was installed in difficult soils and beneath tree roots. A Caterpillar 305 CR 12,000-pound excavator with a specialized hydraulic drive head (10K Pro-Dig) was used to rotate anchors into the ground. The anchors were monitored with a Pro-Dig USA digital torque indicator. Helical extensions advanced the tieback anchors to distances on the sequence of 15 to 21 feet to realize final installation torques. The ultimate capacities of at least twice the design working tension load of 24 kips.
- Fifty-seven (57) additional seven (7) foot SS150 extensions were utilized to reach required load capability due to sub-surface soil variations.
- The helical anchor was connected to a specialized galvanized steel female pivot adapter to which a length of 1” galvanized all thread was attached to a ¾” 6” x 6” square plate. This structural configuration was affixed within the concrete seawall cap. The tiebacks anchors were installed approximately every seven (7) foot with additional anchors at expansion joint locations.