The foundations of homes will rest on soil at levels as decided by engineers during the original construction. The soil conditions at these lower levels can change due to a settlement, wet and dry conditions and other reasons. This can cause cracks in foundations, walls, slabs and other parts of the structure.
In such cases, engineers suggest foundation underpinning that moves the weight imposed by the home from the unstable soil to a support that is more stable. This support is provided through push piers, helical piers, caissons, deep foundation piers and many other systems that can be used to create the required support. In most of these methods, piers are pushed hydraulically into the ground till they reach bedrock. The weight of the home is then transferred to these piers using brackets that act as a connection between the original foundation and the new piers.
Underpinning can also be carried out by increasing the thickness of a foundation so that it has greater structural strength. It is a process that can correct foundations that have developed faults and have settled or show cracks. It acts to make the foundation strong enough to bear the load of the home. You can also use underpinning to increase the bearing capacity of any existing foundation. The right scheme of underpinning a home can depend on the structure that the foundation has. Site restraints, the depth at which the foundation is and other factors like local regulations, cost and time can often lead to decisions on the underpinning to be undertaken for the distressed foundation of a home.
In many cases, where foundations are at shallow levels, the foundation can be strengthened through the pouring of concrete after removal of the weak soil. The concrete replaces the soil and acts a bulwark against the further settlement. Underpinning can also be undertaken by having beams to support the foundation, which in turn are anchored in firm foundations. The use of concrete or steel piles is the most common method of underpinning that is used by most companies who undertake such work. It is a far more reliable method and gives guaranteed results. It also involves less disruption of the home and allows for work to be carried out without any need to evacuate the home, though some amount of disruption and mess cannot be completely avoided.
It is best if all the loads that cause their weight to be transferred to the foundations be removed before any underpinning is attempted. It is also sensible to the fence of the area before undertaking any excavation or other work. Some underpinning work, especially the driving of piles can affect adjacent structures and proper care must be taken to reduce this effect and neighbors informed of the work bring carried out so that they are prepared for any minor inconvenience. Having the right permissions in place can help in this matter as well.
Once underpinning work is completed, you can proceed with the other work to repair cracks and redo any other parts of the home that have been affected by the foundation defects.