St. Augustine Selects Redi-Rock Over Cast-in-Place for Vital Coastal Resiliency Project

Along a vulnerable stretch of Inlet Drive in St. Augustine, Florida, the city needed a coastal retaining wall solution to stabilize and elevate the shoreline in the North Davis Shores neighborhood that had been impacted by coastal erosion. As part of a broader effort to provide greater flood protection for this critical residential roadway, the project also included upgrades to existing stormwater infrastructure and the addition of a tide check valve to help prevent tidal backflow.

Redi-Rock from Truemont Materials provided a solution for the Inlet Drive Shoreline Resiliency Project that allowed the new retaining wall to be constructed landward of the existing waterfront wall, helping limit unnecessary disturbance to nearby mangroves while addressing the project’s cost, constructability, drainage, and aesthetic requirements.

THE CHALLENGE

Repeated storm surge and erosion made a low-lying section of Inlet Drive a priority for the City of St. Augustine.

Map showing the location of the Inlet Drive Shoreline Resiliency Project in St. Augustine, Florida.

The project location is the lowest point in the island chain, where wave action from nor'easters and other coastal storms could push through. Inlet Drive runs along a particularly vulnerable stretch of St. Augustine's shoreline, directly exposed to conditions from the nearby inlet. The risks became especially apparent following Hurricane Matthew in 2016 and Hurricane Irma in 2017.

“That particular section on Inlet Drive that this city owns, we were suffering from erosion, and that storm surge comes in, and it just overtops the road, and it just takes things with it and moves things around… it was a case where if we didn't stabilize that shoreline piece, we were at risk of potentially having a really much larger and very expensive infrastructure problem if that road was to get impacted.” —Jessica Beach, Chief Resiliency Officer, City of St. Augustine

The site's environmental constraints added another challenge. Existing mangroves needed to be avoided, and the project team preferred not to remove the existing waterfront wall. Moving construction farther toward the water could also introduce additional wetland impacts, mitigation requirements, costs, and permitting time.

Finally, an existing storm outfall pipe was allowing tidal water to back up through it, causing road flooding. The project would also need to account for sea-level rise by elevating the shoreline revetment, further addressing erosion, undersized drainage, and tidal flooding. A larger drainage pipe would need to be installed to achieve this goal.

Those considerations led the project team toward a different approach: build the new coastal retaining wall landward of the existing structure.

The new Redi-Rock retaining wall is being installed immediately behind the failing existing wall.

THE SOLUTION

To address the shoreline’s immediate structural needs while supporting its long-term resilience, the City of St. Augustine’s Public Works Department pursued a hybrid strategy combining hard infrastructure with natural shoreline enhancements. Redi-Rock served as the structural component of this approach, providing a new retaining wall designed to stabilize and elevate the shoreline, while living shoreline elements, such as native coastal vegetation, absorb wave energy, reduce erosion, and support the surrounding coastal habitat.

Redi-Rock gave the project team a precast retaining wall option that fit the available footprint while addressing construction, cost, drainage, and aesthetic considerations.

Truemont Materials had begun conversations with the City of St. Augustine several years before construction, introducing Redi-Rock as a potential fit for the project. As the design developed, several characteristics of the system aligned with the city's priorities:

• Smaller Project Footprint. Locating the Redi-Rock wall behind the existing waterfront structure allowed the team to work landward while avoiding the mangroves.
• Simplified Environmental Approach. Avoiding additional wetland impacts helped the project team steer clear of the added mitigation, permitting, cost, and schedule considerations that could accompany a more environmentally intrusive solution.
• Competitive Installed Cost. Cost was a major consideration for the city. Truemont Materials reports that contractors working with the company have seen total installed Redi-Rock costs approximately 30–40% lower than those for cast-in-place walls in comparable applications.
• Efficient Construction. The modular precast system provided an installation approach that helped the project remain on schedule without the onsite forming and pouring associated with cast-in-place construction.
• Integrated Drainage. The wall's drainage characteristics were particularly important in a tidal environment where water may move both toward and away from the wall. The Redi-Rock wall system also allows for the integration of drainage pipes, necessary to upgrade the currently undersized drainage pipe of the existing wall.
• Context-Sensitive Aesthetics. Redi-Rock's textured appearance enabled the design team to create an engineered coastal structure that complemented St. Augustine's historic surroundings.

“When we chose the Redi-Rock, cost was a big driver. The footprint and then the constructability as far as timeline, and then the aesthetics… I've had lots of compliments from our residents. They're like, wow. This doesn't really look like an engineered wall.” -Beach

The appearance was an especially important consideration in a city known for historic coquina construction.

Detailed view of Redi-Rock’s Limestone texture showing similarities to the texture of historic coquina walls found throughout the St. Augustine area.

Laura Mahoney of engineering firm Baxter & Woodman, also appreciated the Limestone-textured wall’s similarity to the area’s natural stone. When you think about the city of St. Augustine, you think of historic coquina walls,” Mahoney explained. “So many structures are made from the coquina, so the way the exterior of the Redi-Rock product was enough similar to that. We felt that it was consistent with what you would see around the city of St. Augustine.”