The process of underpinning targets the foundation when constructing or renovating your home. It involves strengthening the foundation by either extending its breadth or depth. This allows the foundation to rest on a soil stratum that is more supportive by distributing the weight of the house across a bigger surface. Some reasons for carrying out house underpinning are;
- If the original foundation is not stable and strong enough to support the building,
- If the usage of the current construction has changed, and
- Subsidence process that may cause change in the properties of the soil under which the foundation was built.
There are various types of house underpinning methods. Here are the most commonly practiced.
Mass Concrete Underpinning Method
This method has been used for many years with no change in its protocol. It looks to strengthen the foundation of existing structures. Boxes are dug underneath by hand then concrete poured in a strategised sequence. The end result of this process is a strong foundation that is built below the existing foundation. Mass concrete underpinning method is mostly applied for shallow depth foundation systems. It employs the use of utilitarian tools like post hole and shovel diggers. The tight nature of the boxes dug underneath does not allow the use of heavy machinery making it an advantageous method of house underpinning. It employs simple engineering tactics with low costs of labour to produce desired results.
Beam and Base Underpinning
This method of house underpinning employs the use technically advanced adaptation of mass concrete underpinning method. It is done by constructing a reinforced concrete beam above, below, or to replace existing footing. The weight of the building is then transferred by the beam to the mass concrete base that is well constructed at designated and strategic positions. The prevailing ground conditions of the foundation determine the base sizes and depth whereas the size of the beam is determined by configuration of the building and applied weights.
Mini Piled Underpinning Method
The method of underpinning is quite useful for areas that have restricted access, variable ground conditions, where structural movements is minimized, and areas with high levels of environmental pollution. It is highly applicable for cases where weights on the current foundation have to be shifted to stable soils at a higher depth to offer more stability. Rigs specifically designed to work in limited spaces and restricted headroom environments are used to create piles at higher depths.