Injection Piers

Injection Piers

Function: As the name suggests, injection piers utilize a process that injects or pumps a grout solution through the perforated pipes of the pier. Thus, the power of underpinning is combined with the stabilization of compaction grouting to ensure a rock-solid foundation. The injection pier system is a combination of compaction grouting and underpinning. 

  • The injection piers process actually makes the soil much more compact and dense. The more compact the soil, the more strength it provides for the piers. The compaction grout virtually locks the entire underpinning system in place. This process makes injection grouting one of the most stable methods of foundation repair.
  • Each injection pier is specially designed with a perforated pattern on the lower 8 to 16ft of the pier. As the grout is pumped into the soil, it accomplishes several key purposes. First, it provides a water-resistant mass to prevent any downward soil flow. The grout is actually designed to infiltrate soil, and seal the limestone surface so that future ground movement does not affect the piers and ultimately the structure. 
  • Also, as the piers receive their injection, the grout solution spreads into the surrounding soil, amassing a large degree of lateral stability. The additional weight of the grout creates an incredible anchoring force for the piers and for the structure as a whole.

Terminology: An Injection pier is a bracket with a 4ft guide sleeve and 4ft sections of interlocking tubular steel pipes. The bottom 8 to 16 ft of the injection pier is perforated for subsequent ground injection.

Steps to Installation:

  • First, a bracket is installed at each pier location in accordance with the Engineer’s Pin Plan. 
  • Then a large steel frame with a hydraulic ram slides onto the bracket and pushes 4ft sections of pipe down through the opening in each bracket. 
  • The pipes are driven to the bedrock or load-bearing strata, well below the depth of soils affected by seasonal changes in the water table. 
  • After the injection piers have been installed to the appropriate load-bearing capacity, they are hydraulically jacked to sufficiently support the structure.
  • Finally, compaction grout is pumped through the perforated pipes into the soil. Line pressures are constantly monitored to ensure that weak soils are restored and the structure is stabilized. Throughout the pumping process structural movements are monitored at all times.
  • Injection Pier Service Upon completion of this phase, all equipment is removed and all of the injection pier installation areas are filled.