A historic waterfront residence in Poulsbo, Washington, required soil stabilization behind a 135-foot-long concrete seawall built in 1901. Wolden Structural Engineering identified voids behind the 5-foot-tall structure, indicating ongoing soil loss. The project utilized SW-RP1 seawall repair foam to restore stability without replacement.
Initial Assessment
Engineering evaluation documented vertical cracks along the seawall without structural offset, but revealed substantial voids behind the wall. The erosion hazard area designation and 100-year floodplain location required engineered solutions to prevent continued property loss.
Proposed Solution
The design specified expansive polyurethane injection to fill voids and bind soil particles. SW-RP1 was selected for its rapid-setting properties and resistance to water infiltration. The system included 2.5-inch filter drainage ports spaced 5 feet apart to relieve hydrostatic pressure.
Procedures
- Established 26 injection locations at 5-ft intervals along the 135-ft seawall.
- Injected approximately 170 gallons of SW-RP1 resin using controlled techniques.
- Monitored placement to prevent wall crack extrusion.
- Drilled access holes to 6.5-ft depth behind the structure.
- Installed 30 pressure control filters with geotextile filtration media.
- Completed surface restoration within permit requirements.
Results
The three-day stabilization project addressed soil loss while preserving the historic structure. Post-construction monitoring confirmed successful void filling throughout the treatment area. A cost analysis demonstrated approximately 70-80% savings compared to complete reconstruction, while extending the existing structure’s service life by decades and reducing construction duration compared to traditional methods.