SlabJack Geotechnical recently tackled a challenging project in Everett, Washington, where a two-year-old tilt-up panel building faced serious subsidence issues. The building, which featured a 30-foot fill CMU block retaining wall, had settled by 2.5 inches, posing a risk to critical utilities. Initially, compaction grouting was recommended to a depth of 35 feet, but soil tests revealed low blowcounts extended to a depth of 50 feet, requiring deeper treatment than expected and other more economical methods were explored.
The selected mitigation approach was to use NCFI Terrathane Fast Foam (24-042) polyurethane grouting. Injections were performed on a 40 ft by 50 ft grid on the interior of the building, and in rows along the exterior of the building and along the retaining wall. Most injections were performed by drilling holes, each 4 to 6 inches in diameter, and inserting a bundle of injection pipes into the hole. The top-down injection method was used to stabilize the footer, drive lane, utilities, and retaining wall. Polyurethane outcroppings at 30 feet along the retaining wall confirmed successful penetration and stabilization. An independent engineer verified that the settlement had ceased. A total of 50,000 lbs of the 3.5 pcf (nominal) Fast Foam product was injected, with the entire project being completed within 14 business days. More info can be found at NCFI Geotechnical.
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