Tilt-Up Building Stabilized with 50-ft Polyurethane Injections

When subsidence threatened a modern tilt-up panel building in Everett, Washington, Slabjack Geotechnical stepped in with innovative polyurethane solutions and unmatched expertise. Here’s how they tackled this challenging project and ensured the building’s stability for the future.

In Everett, a two-year-old tilt-up panel building faced serious issues. The structure featured a 30-foot fill CMU block retaining wall and had settled by 2.5 inches. The subsidence posed a risk to critical utilities, which had also begun to settle, necessitating immediate intervention.

Initially, compaction grouting was recommended to a depth of 35 feet. However, soil tests revealed low blow counts, indicating poor soil compaction. To address this, the depth was increased to 50 feet to ensure thorough stabilization and effective results.

Slabjack’s approach was meticulous:

• Drilling: They drilled 133 holes, 4-6 inches in diameter, extending down to 50 feet.
• Pipe Installation: Bundles of pipes were inserted at 5-foot increments, backfilled, and prepared for injection using a bucket lift or boom.
• Injection: Click counts were used to inject 40 lbs of polyurethane per pipe. A test shot into sand confirmed the process’s accuracy.

The injection utilized NCFI Terrathane™ 24-042, a high-density 3.5lb polyurethane known for its slow reactivity, optimal spread, and excellent structural support. The targeted areas included:

• Interior Slab: Covering 2000 square feet, extending 8 feet from the wall in a 40 x 50 grid, with 50 interior holes.
• Exterior Areas: Spanning 3000-4000 square feet with four rows of holes, totaling 133 injection points, including 80 exterior holes in six rows.

The top-down injection method proved highly effective, stabilizing 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, showcasing the success of Slabjack’s intervention. Impressively, the entire project was completed within 14 business days by a skilled three-man team, with an additional two-man team brought in during the final phase.

Project Highlights

Location: Everett, Washington
Issue: 2.5″ settlement affecting the building, retaining wall, and utilities
Duration: 14 business days
Team: 3-man team, with an additional 2-man team in the final phase
Total Polyurethane Injected: 50,000 lbs

Slabjack Geotechnical’s innovative techniques and dedicated execution turned a potentially disastrous situation into a triumph. Their deep injection strategy with NCFI Terrathane™ 24-042 not only halted the settlement but also reinforced the building’s structural integrity. This project is a shining example of how Slabjack’s expertise and ingenuity can tackle even the most daunting geotechnical challenges.