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CASE STUDYPELICAN ISLE

PELICAN ISLE YACHT CLUB SEAWALL HELICAL TIEBACK INSTALLATIONPROJECT INFORMATION

Situated on the Cocohatchee River, lies an exclusive Southwest Florida waterfront community, Pelican Isle Yacht Club. Nestled in North Naples at Wiggins Pass, the marina is just minutes from the open waters of the Gulf of Mexico.

Pelican Isle Yacht Club is exceptionally exclusive—it’s a private island with breathless sunsets and constant gulf breezes. The island is home to approximately 136 luxury waterfront units. The 15 acre island has a continuous concrete seawall that surrounds its perimeter.

The dock master of Pelican Isle Yacht Club was informed by boat owners that a portion of existing concrete seawall was rotating out of alignment. In addition, there were numerous locations with sinkholes appearing. Deteriorating sections of the seawall are 40+ years old and the tie-back system has failed.

PROJECT CHALLENGES

The project team was hired by Turrell Hall and Associates, of Naples, Florida to commence structural anchor repairs to the existing aging seawall. Apparently, the salt water currents running in and out of Gulf of Mexico four (4) times per day had taken a serious toll on the foundations structural tie-back anchors.

Fortunately, Coastal Foundation Solutions, an expert helical contractor was quickly hired. But, instead of endeavoring to construct an expensive new concrete seawall, an helical tie-back anchor system was the engineers choice.

Installation was going to be stimulating and challenging, contemplating the natural fundamentals in play.  We encountered a number of methodology challenges including construction in an active marina, limited construction access in the dense marine environment, and complicated access beneath a 8 foot wide dock.

Our company, exceptionally well known for their marine helical piling expertise, turned out to be the precise solution to install the complicated helical tiebacks for this precariously threatened seawall.

HELICAL PILE INSTALLATIONPROPOSED SOLUTIONS

It was established that our helical pile tieback anchor system would have to be steadily drilled through the old concrete seawall. The team would core drill a six (6) inch hole through the concrete seawall to install the proposed helical anchors.

In addition, the engineers had specified a structural composite/aluminum whaler beam to be erected to the front face of the seawall. The beam would be held in place by the helical anchors and stainless steel bolster plates

Consequently, this very confined working area was not accessible from land, so we mobilized one of our modular barges to support and transport our excavator, equipment and crew for the helical/whaler repair.

However, being Florida Natives, we were conscientious in advance of a larger challenge. Each day high tide was going to elevate our operational barge at least two to three foot and once raised, we knew that our drilling mast and installation equipment would be submerged beneath the water. Conversely, our team could only perform from low-tide until just before mid-tide.

PROJECT OUTCOME

Coastal Foundation Solutions proposed solution proceeded precisely according to strategy with no negative consequences. We successfully installed a total of twenty-two (22) 1 ½ in. dia. helical piles, with an average pile length of 17 to 35 foot.  The submerged helical pile installation process took a total of 7 working days, with on-and-off work periods performed in phases. (principally due to tide constraints) Turrell Hall and Associates effectively supervised the entire structural installation process, and managed all the inspections flawlessly. The piling loads included 14 kips (allowable) and each individual helical anchor was load tested.

The structural composite/aluminum whaler was installed during low tide periods and affixed to seawall. The whaler and helical pile combined created a continuous structural support for the seawall. We installed two hundred and twenty foot of whaler material.

PRODUCT
  • Twenty-two (22) Seawall Savers SS150 (1.5-inch square bar) helical tiebacks with a 6”- 6”- 6” triple-helix lead section was installed in difficult shifting tide elements. A Caterpillar 305 CR 12,000-pound excavator with a specialized hydraulic drive head (10K Pro-Dig) was used to rotate anchors. Helical extensions progressed the tieback anchors to distances on the order of 17 to 35 feet to realize final installation torques. The ultimate capacities and design working tension load of 14 kips.
  • Twenty-four (24) additional seven (7) foot extensions were utilized to reach required load capability due to sub-surface soil variations and debris.
  • The helical anchor was connected to a specialized galvanized steel female pivot adapter to which a length of 1” stainless all thread was attached through the structural whaler to a ¾” 6” x 18” stainless steel “C” channel. This structural configuration created a complete horizontal structural whaler system.
  • The tieback anchors were installed approximately every seven (7) foot.

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