On the property of this large high-rise beach front condominium complex, two single story utility buildings began to settle. The block wall utility buildings are approximately 1,000 square feet each, and have a strip footing buried 24 inches deep. The interior of each building was backfilled and a floating slab was poured.
There were visible cracks in the slab of the eastern building, as well as cracks in the walls of both buildings where settlement was occurring. Further investigation showed that the eastern building had a 24-inch-deep void under the rear 10 feet of the slab that had been scoured out during a hurricane. The scour caused the slab to settle approximately 2.5 inches and the foundation to settle approximately 0.5 inches.
At the rear of each building, a 5-foot-wide sidewalk had been undermined by a void and was beginning to crack and settle more than 2 inches in some areas.
To stabilize and lift the foundation and walls, eight (8) Model 288 Galvanized Helical Piers were installed on the eastern building and five (5) Model 288 Galvanized Helical Piers were installed on the western building.
The soil report showed a loose sandy layer at a depth of 14 to 18 feet. Therefore, piers were advanced to 21 feet in order to reach competent load bearing strata. The Model 288 Galvanized Helical Piers were used with a single 14 inch helix. Each pier was hot dipped galvanized due to the high salinity of the soils at the beach. This galvanized material shows less than a 5% section loss over 50 years due to corrosion and will far outlast the structures it is installed on.
In order to lift and stabilize the structure, 20 kip underpinning brackets were used to connect to the 24-inch-thick footing. During excavation, multiple utility lines were discovered below the surface of the soil as well as underneath the concrete slabs. Therefore, piers needed to be installed at the correct angle to avoid the utility lines as well as maintain proper support capacity. Too great an angle would decrease the compressive capacity and too little would hit the lines.
Poly Renewal 400 was used to fill the voids under the building floor slab as well as the adjacent sidewalk. Approximately 880 pounds of Poly Renewal 400 were installed. Both the floor slab and sidewalk were lifted back to their original elevations.