Foundation underpinning is a repair process that strengthens foundations that have been weakened though a variety of factors. In the process of underpinning, the area underneath the load of the foundation is repaired or reinforced for a safer, more stable base.
Underpinning comes in many types and suits many different kinds of repair projects. In order to make the right choice for your project, it is necessary to understand the structure of the foundation, the supports that are used, and the factors that cause the foundation to become damaged.
When Is Underpinning Necessary
Not all types of foundation damages can be repaired via underpinning strategies. This repair method is only required if the foundation cannot fully support the structure that rests upon it. Week and unstable soil is one of the common factors that cause foundations to lose stability.
Sometimes, the soil holding the foundation may become weak due to weathering or necessary excavations. Changes in the structure might also cause the foundation to lose its support efficiency. When you encounter some of these problems, one solution is foundation underpinning.
Underpinning Process According to Type
There are several types of underpinning methods to choose from, though each one is best suited for a particular situation. The traditional mass concrete underpinning method is a good example. This process is best suited for shallow underpinning and involves excavating the weak soil underneath the foundation and replacing it with mass concrete, which provides more strength. Since the concrete base is now stronger than the soil that used to hold the foundation, the weight of the structure is carried in a much more efficient manner.
Another method involves the use of a beam and base. This method not only makes use of traditional mass concrete bases, but also incorporates beams to support the existing foundation. Its load is transferred to a concrete beam that is constructed underneath it. The beam then transfers the load to a mass concrete base, which spreads evenly for support. The construction of the beams depends on the architecture of the structure built on the foundation.
Mini-piled underpinning involves transferring the load of the structure and the foundation to stable soils found deep underground. The depth of the soil exceeds 5-meters. The constructed piles are cased in steel and have a diameter ranging from 15-cm to 30-cm. The piles are driven into drilled holes, making them rest on a stable soil below ground level. Some piles may be constructed as to reach 15-meters below ground.
Setting up Temporary Support
Prior to underpinning, the technicians have to set up temporary supports that will hold the foundation while the underpinning process is underway. These support systems use materials such as wooden boards or steel beams depending on the weight of the load and are removed after the project has been completed.