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Design and Construction of Mackinac Island Harbor retaining walls and columns

Project Name: Mackinac Island State Harbor of Refuge #51

Customer Name: Michigan Department of Natural Resources

Design / Specifying Engineer: Untied Design Associates

Block Manufacturer: MDC Contracting, LLC

Wall Installer: Ryba Marine Construction Co.

Project Location: Mackinac Island, MI

Year Built: 2007

Project Scope

Mackinac Island, known as the Great Lakes' island jewel, is one of the classic historic parks in the United States. Located at the juncture of Lake Michigan and Lake Huron between Michigan's upper and lower peninsulas, Mackinac Island attracts more than one million visitors each year.

The island is accessed primarily by ferry from the towns of Mackinaw City or St. Ignace. Mackinac Island State Harbor is the embarking point for thousands of visitors every day during the summer season. Though the look of the Harbor is intended to be "historic," it was in need of serious renovation. In 2007, the Michigan Department of Natural Resources decided to upgrade the harbor for better functionality and appearance to accommodate the larger numbers of boaters and visitors.

To design and build the new facility at this delicate site, the DNR turned to United Design Associates and Ryba Marine Construction Company, both located in Cheboygan, Michigan.

When the DNR first began looking at options for renovations of the harbor area, they wanted to use natural stone. However, natural stone proved to be cost prohibitive and nearly impossible to install and complete the project within the tight time constraints. The Mackinac Island State Harbor facility was required to meet all Americans with Disabilities Act (ADA) requirements, which made natural stone a poor option due to its irregularity in dimensions.

"The critical points at the sidewalks only had a 3/8 inch tolerance," said Tom Bajko, P.E. from Ryba Marine. "With the ADA requirements for slopes in the sidewalks, this was very important and would have been extremely time consuming to achieve with natural stone."

The design team on this project included Ryba Marine, the State of Michigan, the Department of Natural Resources, and United Design Associates. After studying the budget numbers, ADA requirements, project deadline, and the aesthetics of their options, the design team concluded that Redi-Rock's consistent dimensions, aesthetic appeal, and ease of installation provided the best solution for the project's needs. Redi-Rock's freestanding blocks, columns, and caps were specified for the job to create a picnic area, seat walls, fences to separate green space from roadway, and to provide stable cleats for the moorings of the harbor.

New construction on Mackinac Island is often tricky due to the rich history of the area and the focus on preservation. Mackinac Island was a popular fur trading outpost and saw battles during the Revolutionary War and War of 1812. By the 1860s, the island's industry had shifted to tourism. Travelers from as far as Detroit and Chicago flocked to the island as a natural getaway. In 1875, Mackinac Island was declared the United States' second national park after Yellowstone. The island was transferred to the jurisdiction of the state of Michigan in 1895, becoming Michigan's first state park.

Historic sites across the island have been preserved, allowing visitors to step back in time when they step off the ferry boat at Mackinac Island State Harbor. Mackinac Island has prohibited the use of motor vehicles since 1898, with the exception of emergency vehicles such as a police car and fire truck. Visitors and residents get around by foot, by bicycle, or by horse and buggy.

The project provided some unique challenges for Ryba Marine's construction crew. First, the project's location on an island required transporting a significant amount of materials from the mainland. Second, construction could not begin until the harbor closed for the year in late September, leaving the majority of the project to be completed during the harsh winter months. Third, Ryba Marine had never installed Redi-Rock.

"The learning curve for installing Redi-Rock was minimal. The workers had to learn as they went and did not have the luxury of any spare time to learn," Bajko said. "This is a first time installation that came out quite well."

The Redi-Rock blocks were manufactured in Charlevoix, Michigan by MDC Contracting and transported about 60 miles to the ferry dock in St. Ignace, Michigan where they were loaded onto a barge bound for Mackinac Island. The island's streets were not used at all to deliver the blocks and the machinery used to construct the project was located on barges to preserve the shore. In total, 1,300 Redi-Rock blocks equaling 650 tons were unloaded on the shore and installed as the project progressed. MDC worked very closely with Ryba Marine to insure the proper blocks were delivered at the right time to keep the project on schedule.

"It was very important to have the shop drawings and block counts due to the logistics of the project," Bajko said.

The freestanding blocks used in this project weigh about 1,500 pounds each and are installed using heavy equipment like an excavator, skid steer, or backhoe and a small crew. The Redi-Rock system is designed with interlocking knob and groove blocks that allow for mortarless installation. The freestanding blocks are textured on two sides and the end blocks are textured on three sides. The caps, textured on four sides and the top, are placed on top of the freestanding blocks to create a "polished" look.

Curved freestanding blocks created pedestrian overlooks facing the water, featuring four different radii, ranging from 16 feet to 56 feet. Curved freestanding blocks are produced with special inserts that eliminate the need for cutting the blocks on the job site. The minimum radius is 14'6" when all curved Redi-Rock blocks are used. Variable radius curves are available with special inserts and trimming the block as needed. The designers included some creative touches in the project, including using Redi-Rock's freestanding blocks to make benches for visitors to rest and enjoy the view of the harbor.

The boat cleats at the end of the harbor's docks needed to be anchored to a stable structure, ensuring the boats safe haven amidst the sometimes harsh conditions of summer storms. To give the boats the strong anchor they needed, the designers of this project found a unique way to make the Redi-Rock freestanding garden blocks act as an anchor for each dock's cleats.

The garden blocks were attached to the concrete sidewalk using 1" threaded bar. Garden blocks have the same basic design as a regular freestanding block except the top of the garden block has a 7-1/2" trough. This trough is typically filled with soil and planted with flowers or other ornamental plants. However, in this application Ryba Marine filled the planter area with concrete. While the concrete was still wet, Ryba placed caps with re-rod on the bottom to secure their position. The boat cleats were then attached by drilling into the caps where bolts were epoxied in place. This creative combination completed a secure cleat for boat to moor in the harbor.

To encourage a better flow of pedestrian, bicycle, and horse and carriage traffic through the park, United Design Associates designed a series of fences integrating Redi-Rock columns connected by fence rails. These columns feature the same cobblestone texture as the freestanding blocks, tying the entire project's look together. Redi-Rock caps top off each column.

Through the creativity and hard work from the design and construction team, the Mackinac Island State Harbor renovation was completed on May 15, 2008, just in time for the kick-off of the 2008 tourist season on the island. In addition to the Redi-Rock installation, the project also included construction of all new utilities, dredging, piling, structural steel including electrical, water, and sanitary on shore and on the pier, mooring system and structural repairs, new shoreline riprap, new finger pier, landscaping, and a new marina building. The total contract was over $5.2 million. The Mackinac Island State Harbor Refuge was rededicated on June 19, 2008, and serves as an example for future harbors of refuge in the state of Michigan. For a live look at the completed marina, visit 

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