It is a process of installing a system of piles to give extra vertical support under the foundations of various existing structures, where the soil is failing to carry the required loads.

The first sign is the appearance of structural wall or floor slab cracks that indicate loss of support from the soil below the foundations. The cause could range from, underground water, white ant nests, old decaying tree stumps below the footings, various soil types and most common of all is builders who have not dug the foundation trenches deep enough and cast the footings in the loose fill material that is still in its process of consolidating. The shape, size and position of the crack pattern will indicate where and what must be done.

The system we prefer is Jacked Piling, where steel pipes are jacked into the ground directly below the center line of the wall until there is an upward lift and then the pipe get concrete.

This steel lined concrete shaft which has founded on the rock below (or suitable load bearing soil) is then loaded with the weight of building above, by using hydraulic jacks and a system of wedges.

This transfers a positive upward force into the building which ensures no further settlement. With this hydraulic jacking system, we can sometimes close the cracks and also record the working loads at each pin position. If this force can lift the building it will be able to hold the building.Don’t underpin and hope it will work.  Underpin and be sure !!

The most common method that is adopted by builders is the use of Mass Concrete that is poured under the foundations, An attempt is made to increase the area of the foundation bearing area of the footing to reduce the pressure on the soil below. It is vital that the excavation goes through any made up ground and find any natural ground or suitable ground to carry the load. The added weight of the mass concrete founded in the ground may exacerbate the settlement. Any previous underpinning attempts will need to be demolished  to accommodate the new piles.

The next most common method is called the auger  or Haunch pile which is a round hole that is augured as close as possible to the wall with a supporting shoulder protruding under the footing. This is filled with reinforced concrete.

With both these methods one has to contend with the fact that concrete shrinks before it cures and that the building above will experience further settlement before it loads these piles. One will have to wait a good few months for the movement to cease before the remedial work on the wall cracks can commence. Both systems can work in the right conditions but with careful quality supervision and only be carried out by competent underpinning specialists and repair contractor.