Problem
The seawall along the Lake Michigan shoreline in Manitowoc, Wisconsin, had been suffering from ongoing settlement and soil loss through gaps and holes in the structure, requiring the city to repeatedly backfill with rock several times each year. These temporary measures failed to address the underlying cause: subsurface soil piping and erosion.
Dynamic Cone Penetrometer (DCP) testing identified multiple zones of loose and unstable soils extending to depths of approximately 10 feet. These conditions were likely made worse by seasonal freeze-thaw cycles and the heavy toll of industrial barge docking impacting the seawall to support a local malt facility.
Solution
RaiseRite proposed and executed a polyurethane permeation grouting program using a single-component polyurethane grout with minimal expansive pressure to seal the gaps through which soil loss was occurring and stabilize the failing soils without excavation or disruption to the seawall structure.
Project Details:
- Treatment Depth: 2 to 9 feet, effectively treating soils down to 10 feet.
- Coverage: 80 linear feet of seawall treated.
- Material Used: Approximately 1,500 lbs of single-component polyurethane grout.
- Crew: 2 technicians from RaiseRite.
- Timeline: 2 days for initial DCP testing and treatment; 1 follow-up day for post-testing.
Using a modified paint spray pump, injections were performed at one point at a time to ensure tight control over depth and volume. RaiseRite also deployed containment netting and boom systems along the shoreline to prevent foam migration into Lake Michigan — resulting in minimal cleanup and no environmental discharge.
Results & Verification
Post-treatment DCP testing revealed a threefold increase in resistance, demonstrating a significant improvement in subgrade stability. The injection process effectively stabilized loose soils, filled voids, and mitigated the conditions leading to seawall settlement.
Key Outcomes:
- 3x increase in DCP resistance post-injection
- Eliminated need for recurring backfilling
- No excavation or heavy machinary required
- Environmentally contained application
Summary
This seawall stabilization project in Manitowoc showcases RaiseRite’s ability to deliver effective, low-impact soil solutions for waterfront infrastructure. The polyurethane injection strategy not only restored structural stability but also eliminated recurring maintenance and preserved the integrity of the surrounding environment.
RaiseRite’s precision execution — from testing through post-verification — highlights the value of polyurethane grouting as a long-term solution for seawall settlement and subsurface soil loss.
