Case Study - Warehouse Slab Leveling

The owner of a gas manufacturing facility contacted a Georgia-based contractor regarding significant floor settlement issues, with a warehouse slab dropping approximately 3-4 inches. The settlement made issues for the forklift traversing in and out of the warehouse and posed a risk to the workers.

Initial Assessment

Upon arrival at the site, the team conducted a thorough investigation. Using a probe, voids were identified beneath the slab, with the probe sinking up to 2 feet in some areas. A Dynamic Cone Penetrometer test revealed large voids 2-4 feet below the slab.  Poor drainage was evident, with improper crowning causing water to flow towards the building instead of away from it. Interestingly, a layer of unusually hard clay was noticed outside the building, suggesting possible prior remediation attempts.

Proposed Solution

AP Lift 430 was chosen for this project, providing an excellent injectable polyurethane grout solution. With its impressive 22x expansion capability and 7,200 psf compressive strength, it’s ideal for warehouse slabs that support heavy equipment. The grout’s hydrophobic properties ensure long-term stability by blocking water infiltration that could otherwise lead to void formation.

Procedures

1. Deep Injection (Void Fill)

• 32 injection points were established in a grid pattern (16 on each side) at 4 ft apart.
• At each point, the team injected 15-20 pounds of material at about 5 feet depth.
• A slight lift (approximately 1/16 inch) during this phase indicated successful void filling.

2. Slab Lifting

• Additional holes were drilled next to the wall, 3 feet from the wall, and 9 feet from the wall (6 feet from the first row).
• Injection began from the holes nearest to the wall and moved outward.
• Multiple passes were made, with some areas requiring 3-4 injections.
• Gradual lifting was employed to prevent slab cracking.
• Dial indicators were used to ensure even lifting across the warehouse floor.

Results

The project successfully stabilized the warehouse floor and restored it to its proper level. Effective void-filling addressed the underlying instability, providing a solid foundation for the slab. Success was evident in the restored functionality of the warehouse space and the elimination of safety hazards posed by the uneven floor. The property manager was pleased with the work and requested additional slab lifting services for their other facilities.

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