Underpinning Techniques for Strengthening a Building's Foundation

Underpinning is a method that is used to strengthen a building's foundation for many different reasons. It could be that a building owner desires to expand a current structure, or the current foundation is visibly damaged and faulty. Underpinning services provide critical advice on the process of strengthening a current foundation and the most efficient methods that can be used to achieve this goal.

There are several commonly used techniques for underpinning a building. The most common and effective methods include:

• Mass concrete underpinning
• Pier and beam underpinning
• Mini-piled underpinning
• Underpinning by needle and beam

Let's look at each method in more detail, as well as the advantages and disadvantages of each.

• Mass concrete underpinning

Mass concrete underpinning is the traditional underpinning method that is commonly used to strengthen a building's foundation. It involves extending the foundation of the old building until a stable equilibrium is reached for the new structure.

Also referred to as the pit method, concrete underpinning begins by excavating the soil beneath the existing foundation while installing pins on the underlying structure. The soil is removed in a strategic manner and on a step-by-step basis.

When enough pins have been added to achieve a stable equilibrium, the excavation can be filled with concrete to seal the existing hole. A dry cement pack is normally used to provide support to the new pins that have been added.

• Pier and beam underpinning

The mass concrete method works best for buildings with shallow foundations, but what happens when you have a building with a deeper foundation? The pier and beam underpinning method suits this purpose well because it involves the installation of piers and beams underneath the surface of the building to provide added support to the structure.

The beams can have varied sized and depth depending on the load that they are supporting. This method works best for depths that do not exceed 6 metres.

• Mini-piled underpinning

For foundation depths that exceed 5 metres, the piled underpinning method can be used to drive piles of between 1.5-3m below the surface. This technique works best for soil that has variable characteristics, and it achieves general weight redistribution in the current structure.

• Underpinning by needle and beam

The needle and beam underpinning method is an extension of the mass concrete method. Once a pin is installed in the underlying building structure, a needle beam can be laid out horizontally to provide added support to the existing beams that are holding up the building.

The needle and beam method can therefore be used to make up for any shortfalls that the mass concrete method may provide. For more information, contact a local concrete contractor.