The clear advantage of jacking a pile as an underpinning technique is the lack of any vibration.
The reaction used is the building wall loads. A slab or series of beams are needled into the wall in advance of pile insertion. Piles are installed through holes left in the reinforced concrete works.
Usual pile loads of 250 to 500KN. This system can be specified only after a check that obstructions to the pile penetration will not be found, as jacked piles have a limited ability to penetrate past obstructions and repositioning is relatively expensive.
The transfer of load from the building to the piles may be by slab needled into the walls or beams either side of the wall. As this work is done in advance of the jacked piling it already produces a degree of structural support prior to any piling works.
Sections of pile are connected using specially machined interference fit couplers.
Box outs in the slab/cap are filled with high strength grout on completion of the jacking works.
This type of piling is used in underpinning works where the structure may be sensitive to vibration or in distress requiring a very low risk solution.