Foundation Underpinning Process Explained

Foundation underpinning is a repair process that strengthens foundations which have been weakened by a variety of factors. In the process of underpinning, the area underneath the load of the foundation is repaired, made strong or reinforced.

Underpinning comes in many types and suits different kinds of repair projects. In order to make the right choice, it is necessary to understand the structure of the whole foundation, the supports used and the factors that cause the foundation to crack or get damaged.

 When Is Underpinning Necessary

Not all types of foundation damages can be repaired through underpinning strategies. This repair method is only required if the foundation cannot fully support the structure constructed on top of it. Week and unstable soil is one of the common factors that cause foundations to loose 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 loose its support efficiency. When you encounter some of these problems, one solution is to make use of foundation underpinning.

 Underpinning Process According to Type

There are several types of underpinning methods to choose from, and each will be best for some situations only. The traditional mass concrete underpinning method is a good example. The 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 makes use of the traditional way of constructing mass concrete bases but also incorporates beams to serve as a support for 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 it evenly for support. The construction of the beams depends on the architecture of the structure built above the foundation.

Another type of underpinning process, called mini-piled underpinning, involves transferring the load of the structure and the foundation to stable soils found deep under the ground. Usually, 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 being carried out. These support systems make use of materials such as wooden boards or steel beams depending on the weight of the load. The supports are removed after the completion of the underpinning project.