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CASE STUDYBONITA BEACH FOUNDATION STABILIZATION

UNDERPINNING PILES FOR EXCEPTIONAL SUPPORTPROJECT INFORMATION

ANALYSIS

After Hurricane Ian, countless beachfront and coastal homes throughout the west coast of Florida have required extensive foundation work due to soil washout and erosion from the associated flooding. This beachfront home in beautiful Bonita Beach in Bonita Springs, Florida required an underpinning solution following the storm, and our team was happy to assist.

SOLUTION

With helicals being the logical choice in providing the support needed for this beachfront home, our team mobilized and performed a static load test in March of 2023. Utilizing Helical Micro Pulldown Piles, our original test piling secured 32 tons in compression and traveled to 34 feet, securing 4,800 ft/lbs of torque (which translates to 24 tons in compression). The installed 5″ grout column provided an additional 8 tons of compressive strength, netting the installed piling approximately .592 KIPS.

As we have worked previously on this project and have extensive knowledge of the subsurface conditions in this location, we crafted a plan to install additional piles and underpinning pilings to secure the internal portion of the existing residence.

RESULT

Our team installed 28 total underpinning piles around the perimeter of the structure. However, onsite excavations to locate the footer were only preformed to two (2) foot beneath grade. The architect elected to install new foundation piles instead of underpinning piles on perimeter grade beam.

Coastal Foundation Solutions commenced installation of perimeter piling and encountered a grade beam. The various grade beams are approximately 30-36 inches beneath the existing grade. The existing grade beam is approximately 30” wide by 12” deep with four (4) # 6 pieces of reinforcing steel.

Coastal Foundation Solutions dug exploratory holes and uncovered the grade beam to determine size and condition. Upon excavating underneath the footing, we encountered a large amount of water flowing in from both directions underneath the footing. We believed this to be ground water infiltration due to proximity of The Gulf of Mexico and adjacent canal system. This discovered water underneath the footing required 22 hours of excavation and dewatering.

On the interior of the project, we installed 20 Underpinning Pilings. These pilings will provided immense support the the home’s foundation and increased its load carrying capacity substantially.

PRODUCTS

On this project, we installed the following:

New Foundation (Interior)

Installed (20) SS150 8” x 10” x 12” 76″
2 Piles were met with “refusal” at 18 foot.  Each required a 16” Helix extension.
2 additional 16” Helix extensions were installed as well, for a total of 4.

New Foundation (Exterior)

Installed (28) SS150 8” x 10” x 12” 76″
12 Piles were met with “refusal” at 18 foot.

“Refusal” or “Spin- out” of a helical pile occurs when the pile refuses to penetrate while continuing to rotate during installation. Spin-out can occur when the soil’s resistance to penetration exceeds the downward thrust generated by the helix plates and the crowd pressure applied by the 28,000# excavator. Spin-out usually occurs at the conversion between a dense soil layer and bedrock when the helix plates confront hard/very dense material. Helical pile spin-out (refusal) affects the load capacity, and the means to predict said capacity via torque correlation. Once the helical pile tip (3.5” Diameter) encounters lime rock, the installation torque can no longer be commuted. The digital torque indicator may only record as the helical pile is progressing and creating torque resistance. Therefore, the bearing capacity of spin-out piles can only be determined definitively with an actual static load test. When the helical pile has spun-out on bedrock, the capacity can be assumed to be limited to the structural strength of the bottom-most helix plate – assuming the bedrock is strong enough to bear the load. In this representation, the lower most helix plate reflects the following design perimeters.”

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