The Process of Foundation Underpinning Explained


Underpinning can be described as a building technique used to strengthen a weakened or unstable foundation due to various reasons.

The process used in underpinning involves repairing or reinforcing the area beneath the foundation for a more stable and safer base.

Underpinning is done using different methods. Each underpinning method is suitable for specific foundation problems. It’s necessary to know your foundation’s structure, the kind of supports holding the foundation, and the causes of the foundation damage.


victorian house after underpinning foundation


What Necessitates Underpinning?

Some foundation issues may not be repaired by underpinning. Underpinning is only ideal for fixing a foundation that is no longer strong enough to support the building resting on it. Unstable or weak soil is a common cause of a weakened foundation.

Sometimes, the underlying soil on which a foundation sits can weaken as a result of excavations or weathering. The foundation can also lose its efficiency as a result of making alternations in the building it supports. If you encounter such problems, underpinning might be the best solution.


Underpinning Methods

There are several underpinning methods available today. Each method is suitable for a specific situation. Tradition underpinning, also known as mass concrete method, is one of the oldest underpinning methods.

It’s suitable for shallow applications. In this method, the soil beneath the foundation is excavated. The excavated soil is replaced with concrete to provide the foundation with a stronger base. Since concrete offers a more solid surface for the foundation, its weight is carried on a stronger base.

Another popular underpinning method is known as the beams and base method. In this method, a concrete base is used in combination with beams to offer more support to an existing foundation.

The load on the foundation is thereby transferred to the concrete beams installed beneath it. The beams transfer this load to the concrete base.

The concrete base spreads the load evenly for more stable support. The beams are constructed depending on the structural design of the building.

Mini-piled method is yet another underpinning technique. The technique is applied by transferring a foundation’s load to a more stable soil deep in the ground. In this case, the soil depth should exceed 5 meters.

Underpinning piles come in steel casings. The piles feature a diameter of between 15 to 30 centimeters. During the mini-piling process, holes are drilled into the ground and piles driven through them until they sit on more stable soil. In some cases, the piles can go 15 meters deep.


Creating Temporary Support

Before underpinning, the builder will create temporary supports to hold the weak foundation while underpinning the house. The support systems are made of materials like steel beams or wooden boards.

The kind of support system material to be used depends on the structure’s weight. The supports are removed upon the completion of the underpinning project.


Also read: Does Your House Need Underpinning?