Deep-drilled concrete piers reinforced with rebar are drilled 9 to 15 feet into the soil under foundation grade beam. Depending on soil and loaded weight of foundation, single 12 in. piers or double shaft, 8 in. piers are placed- usually on six-foot centers.
After piers are hardened and cured to a PSI strength of 3,500 PSI, jacks are placed on pier caps and concrete blocks are placed between the foundation and pier caps. Steel shims are used as spacers. Concrete piers are adjustable.
Concrete piers are a preferred method when foundation is of a poor quality. Pressure is only applied to foundation during the lifting process.