A single-story office building settled over organic soils beneath its post-tensioned slab. With access restricted to the interior, a fast and clean repair was essential. Geotech experts from Helicon were called in to assess the situation.

Initial Assessment

Borings showed dense to very loose strata and differential movement under interior columns and slab zones; uniform densification and code‑level lift tolerance were required. Traditional underpinning inside an occupied shell would extend schedules and raise costs versus targeted polyurethane injection.

Proposed Solution

The contractor selected AP Lift 475 for hydro‑insensitivity, rapid ~15‑minute reaction, and ~100 psi compressive strength (~14,000 psf). This material was ideal to permeate, densify, and lift with minimal downtime.

Procedures

1. Inject 30,000 lbs over 635 interior points per geotech layout.
2. Apply tight grid spacing, pressure/volume control, and real‑time elevation checks.
3. Coordinate QA/QC with the Engineer of Record for sign‑offs.

Results

• Restored slab support and column bearing
• Zero exterior disruption; interior‑only access.
• Approximately 97% cost savings vs interior underpinning/piering, with faster completion.

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