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CASE STUDYNORTH CAPTIVA ISLAND CLUB

HELICAL INSTALLATION FOR NEW SEAWALLPROJECT INFORMATION

In January of 2015, Coastal Foundation Solutions was contracted to install a series of helical tieback anchors in a new seawall for the North Captiva Island Club. Undiscovered and remote, North Captiva Island is accessible only by boat or ferry. This island community is reminiscent of an old Florida beach town, as life was in a simpler time. Located just 3 miles offshore of Pine Island, the tropical barrier island is part of Southwest Florida’s barrier island chain. The island is strewn across an expansive preserve and known worldwide for its vacation retreat status. There are no cars on the island, residents and visitors travel by golf cart or bicycle on lovely sandy trails.

The owners elected to construct a twenty-two slip marina, which required installing 300 foot of concrete seawall and dredging of 5000 cubic yards of material. The project would entail creating a new boat basin and docking facilities on Captiva Island.

The owners contracted with Florida Marine Construction to construct the new marina facilities.

PROJECT CHALLENGES

The layout of the marina basin was in exceptionally close proximity to Mangos Café and Grill (8 foot). Directly adjacent to the project site was also a two story watersports rental facility.  This presented a problem with construction of the new concrete seawall. Conventional concrete deadman and tie-backs could not be utilized. The anchors as designed would be required to be installed beneath the two, 2 story buildings.

This would require multiple mobilizations and a delay in installing the new seawall cap as the concrete has to cure for 7-10 days, Barrier Island installations are often in remote areas requiring materials to be shipped in over long distances.

Florida Marine Construction contacted Coastal Foundation Solutions for consultation and recommendations.

HELICAL PILE INSTALLATIONTHE SOLUTION

We recognized that this was an issue which required immediate attention so the project could proceed on time. Once the issue was identified, Coastal Foundation Solutions secured the services of Ruben Clarsen Consulting to provide engineered plans for the helical anchor tie-back installation.

Coastal Foundation Solutions proceeded exactly as planned with equipment mobilization to Captiva Island with no delays or interruptions. We maintain a fleet of modular barges to be transported into any type of waterbody, even land locked lakes.

The design entailed installation of forty-eight (48) 1 ½” square shaft Seawall Saver helical anchors placed on 7 foot centers. Additional anchors were required to be installed on each immediate side of expansion joints.

The helical tie-back anchors and installation equipment were transported to Captiva Island by Coastal Foundation Solutions custom construction barge. The new seawall panels had been installed and access from the upland portion of the project site was non-existent. Thus, the helical tieback anchors were installed with specialized equipment mounted to a hydraulic excavator.

PRODUCTS

Forty-Eight (48) Seawall Saver (1 ½” inch square bar) helical tieback anchors with a 6”-6”-6” triple-helix lead section was installed over the top of existing concrete seawall slabs. Coastal Foundation Solutions utilized a Caterpillar excavator with a specialized mast system powered by a 6K Eskridge drive head to install the helical anchors. Seawall Saver Helical extensions imbedded the tieback anchors to lengths of 15 to 21 feet to attain final installation torques.

The helical tieback anchors were hydraulically rotated to 2,000 P.S.I., providing a tension load of 12 kips.

One hundred and twenty-two (122) additional 1 ½” extensions were used to attain dynamic load capacity due to sub-surface soil disparities.

The helical tie back anchor was linked to a hot dipped galvanized “C” steel channel, placed within the seawall cap to provide lateral structural support. All tiebacks and anchors were installed with a Digital Torque Indicator to insure required engineered load capacity.

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