Oxford Manor Apartments has a building which had up to 3" of settlement inside the structure. Polyurethane grouting and underpinning has previously been performed to lift and level the floors in the structure. Shortly after the repairs had been made the cracks in the floors, sheetrock, and brick reopened. Due to the amount of settlement in the structure the units were unable to be rented and needed a quick lasting fix. Alpha Geotechnical and Testing Services did an investigation to determine the cause of settlement and found the presence of expansive soils on site to a depth of 25'. Further, it was determined the previously installed underpinning elements were not sufficiently supporting the structure.
Due to low overhead inside of the building and limited access around the perimeter of the structure, Alpha Geotechnical determined it would be best to support the entire structure with hydraulically-driven piers and helical piers.
A helical pile configuration of 2-7/8" outside diameter round shaft, with an 8"-10" double-helix lead section was selected to support the foundation at the perimeter of the structure. The perimeter piles were installed with a Bobcat E35 mini-excavator. The interior of the structure was supported by 2-7/8" outside diameter round shaft driven piers attached by a slab bracket.
The correlation between installation torque and driving PSI was monitored throughout installation to determine the capacity of each of the piers. The installation of 118 piers throughout the structure only took 2-1/2 weeks.