Project Overview
Dean Marine and Excavating partnered with NTH to form a Design-Build team in pursuit of the rehabilitation of 600 feet of seawall at 1351 W. Jefferson, in downtown Detroit, MI. This former rail yard parcel had an existing 1910’s era Wakefield Sheeting timber and concrete capped seawall that had been in an observable state of deterioration for many years and was believed to be the source of significant subsidence along the shoreline. The City and DDA had committed to support plans to construct an extension of the Detroit Riverwalk over the DDA property at the river’s edge by constructing a stable replacement or modified seawall solution.
Project Scope
The bridging documents contained in the Design-Build RFP included limited geotechnical and dive inspection data. NTH performed historical document research, conducted a geotechnical investigation consisting of test borings and test pits, conducted a Phase II Environmental Site Assessment, prepared a Baseline Environmental Assessment, and directed a supplemental dive inspection of the existing wharf to fill in data gaps. NTH also relied on geotechnical data from file at adjacent sites. Young’s Consulting conducted a bathymetric survey under contract to Dean Marine to supplement available topographic survey data.
The investigation revealed the presence of tiebacks and timber anchor piles that were integral to the performance of the existing seawall system. The test pits and dive inspection revealed the wharf was in fair to poor condition. Large gaps were noted in the Wakefield sheeting with evidence of soil loss between the boards. Intermittent contact was noted between the heads of the timber support piling and the concrete bulkhead throughout the wharf and 50 feet of the wharf at the upstream end was in critical condition due to missing tiebacks, highly damaged or fallen timber wale beams, and missing timber support piling.
NTH recommended and design a replacement seawall consisting of an anchored sheet pile wall utilizing a sheet pile deadman system, steel wale sections and high strength steel anchor rods. Following completion of the design, NTH prepared and submitted the joint USACE/EGLE permit and Wayne Count SESC permit applications on behalf of the owner. Throughout construction, NTH staff regularly visited the site and was in frequent contact with Dean Marine to resolve issues that developed as a result of high-water levels and previous shoreline systems at the site.
Client Benefit
NTH worked with the DDA and Dean Marine to develop a design that met the structural requirements for the site within forecast budgets. NTH’s approach to perform a holistic review of the site to include historical documents and fill data gaps resulted in a significant change in the project scope from repair to replacement to the benefit of the DDA. NTH developed a cost-effective design that considered both the historic high and low water levels, coordinated with the needs of the Riverfront Conservancy, and included construction details developed in concert with Dean Marine to advance the schedule and remain an economical solution.
