Algoma Harbor is a recreational harbor on the western shore of Lake Michigan that is approximately 30 miles east of Green Bay, Wisconsin. The channel is protected by a 1,102-foot north breakwater and a 1,530-foot south breakwater. Both breakwaters needed repairs due to deterioration of the timber cribbing and loss of stone fill, which led to voids in the breakwaters and increased channel sedimentation.

The U.S. Army Corps of Engineers Chicago District chose Hanson, as part of a joint venture, to design a partial demolition of the breakwater caps, a full steel sheet pile (SSP) encapsulation of the breakwaters and the construction of new reinforced concrete top slabs, which will approximately match the top of the cap elevations.

The SSP solution

Because the timber cribbing and cap were showing signs of deterioration and loss of fill, the team’s recommended repairs consisted of partial cap removal and full SSP encapsulation, which will stabilize the timber cribbing and allow the construction of a new reinforced concrete top slab.

Additionally, to install the SSP, the project team recommended temporarily relocating armor stones that surround the lake and harbor sides of the south breakwater from the edge of the breakwater, so the sheet pile driveline is clear.

The design calls for the following:

  • the installation of the SSP on both sides of the existing breakwater
  • the placement of new stone fill material between the SSP
  • the installation of a permanent waler and tie-rod system at consistent spacing to provide additional lateral stability for the SSP
  • the construction of a reinforced concrete top slab in between the SSP

The team recommended that the SSP for the repairs be hot-rolled PZ steel sheet piles, which are appropriate for the repair because of their interlock strength and overall yield strength characteristics.

Preserving historic elements

A historic lighthouse sits on the eastern end of the north detached breakwater, and the project team developed final condition lighthouse support details to provide the lighthouse with vertical and lateral stabilization throughout construction.

Additionally, the eastern end of the north attached breakwater features a historic catwalk structure that provides a walkway between the north land attached breakwater and the north detached breakwater and was previously used to provide access to the upper lighthouse door. The construction plans include removing the catwalk to facilitate construction of the sheet pile breakwater structure.