To make way for a planned City of Detroit park and Riverwalk extension, a site remediation project is underway on nearly 500 feet of former industrial land along the Detroit River near Fort Street, downstream of the Ambassador Bridge. As a subconsultant to Stantec, Wade Trim provided regional seawall design expertise and construction oversight on that portion of the remediation project.

While the seawall was originally built to retain the soil on the land side down to the river’s dredge line, the site remediation required excavating this same soil 30 feet deep while the seawall held back the river on the other side. An initial condition assessment and engineering evaluation of the seawall and buried components was undertaken to understand existing site conditions and develop design alternatives.

A unique approach was used to excavate 15,000 cubic yards of soil while maintaining the seawall’s structural integrity. A king-pile wall was installed 30 feet inland, parallel to the seawall. Then six mini-cofferdams, or cells, were created between the two walls to isolate small areas for excavation. In sequence at each cell, soil was dredged and removed, and the cells were kept full of water which maintained nearly equal pressure on both sides of the seawall. As the impacted material was removed between the walls, a 10-foot-thick concrete matt was installed using a tremie method. This slab, along with a series of struts and braces, created a composite wall assembly, providing permanent shoreline protection and a base for the future Riverwalk path. The site remediation project is expected to be completed in the spring of 2019.