Seawall Sinkhole Stabilization in North Carolina

Problem

Hatteras, also known as Croatoan Island, is a barrier island located off the coast of North Carolina. The island’s 50-plus miles of beautiful shoreline make it a popular tourist destination with over 50,000 visitors per week in the summer months. One of the primary ways to reach the island is via the Cape Hatteras Ferry. When sinkholes formed behind the ferry terminal’s seawall, the North Carolina Department of Transportation (NCDOT) began to search for a way to prevent further sinkhole damage and ensure safety to the area.

Analysis

The seawall consisted of concrete support piles and concrete panels. The panels were set and sealed in between the piles, but the failing seals at the ferry terminal were causing soil to pull through the wall and into the ocean. As a result, sinkholes formed behind the seawall. The NCDOT contacted URETEK for an environmentally friendly, non-invasive solution to prevent further loss of soil behind the seawall at this important point of entry for the island.

Solution

URETEK employed its URETEK Deep Injection® (UDI) process along the seawall to fill the voids and sinkholes with expanding, water-resistant polyurethane. This process also sealed the panels and piles on the back side of the wall, preventing the future formation of sinkholes. Trained divers located the joints of panels while also providing a live-stream video of the repair process for quality assurance. Then, injection tubes were driven down to 20-foot depths along the seawall, and technicians began to inject URETEK 486 Star® polymer.

Result

With the UDI repairs, all soil leaks were successfully sealed, the sinkholes forming behind the wall were filled, and the soil was stabilized. The URETEK crew took extra precautions during injection into this environmentally sensitive area to guarantee the project was ecologically friendly. The newly sealed joints provided a stable and functioning ferry terminal for residents and vacationers visiting Hatteras island.

URETEK Deep Injection® (UDI)

Widely referenced throughout our industry, UDI involves the injection of structural polymer into base and subgrade soils to increase the load bearing capacity. This is achieved by injecting the polymer through small holes drilled directly through the pavement structure to depths determined by site-specific analysis. Our URETEK 486 Star® material flows easily into voids and weak zones within the soil mass below. Through a controlled chemical reaction, the expanding polymer compacts surrounding soils and applies a controlled pressure on targeted areas of the affected pavement above. If needed, a multi-injection design plan is utilized to gently return the pavement to its original grade. The composite material quickly cures into a strong, dimensionally stable, and water-resistant geo-material, providing years of reliable service.

URETEK 486 Star®

URETEK 486 Star® polymer is a two-component, high-density, expanding thermoset polyurethane system. It was developed to be the ideal solution for under-sealing, void filling, lifting of settled pavement, stabilization and stiffening of weak soils, and for encapsulating and sealing buried infrastructure. URETEK 486 Star® is environmentally inert, non-toxic, and resists underground water erosion or weakening due to its industry-leading hydrophobic properties.

Seawall Sinkhole Repair
Sinkhole Repair
Sinkholes formed behind the ferry terminal's seawall
Sinkhole repair
UDI was performed along the back side of the wall to prevent the future formation of sinkholes