Types of underpinning for foundations
If the foundation of your home can no longer provide support, you may be required to carry out underpinning. In construction or renovation, it is the process of strengthening the foundation of an existing building. A building may require underpinning for a number of reasons which include the following:
- The original foundation is faulty or not stable enough.
- Weight, such as an extra storey, is being added on to the structure
- A change in the properties of the soil surrounding the foundation
- Construction of nearby structures that requires soil around existing structures to be excavated.
- To increase the depth of existing foundations
- Movement of the foundation as a result of earthquakes, floods or other natural causes
- Soil subsidence which has caused the foundation to sink.
Available underpinning methods
The reason why your foundation requires underpinning is an important indicator of the method to use. And while underpinning services are carried out by specialists, having some little knowledge will help you make the right decision when you receive quotations from structural and geotechnical engineers The methods available for strengthening your foundation may, among others, include the following.
Beam and base underpinning
This is a more technically advanced variation of concrete underpinning that involves construction of a reinforced concrete beam either below or above an existing one, or in replacement of the existing footing. Mass concrete bases are then constructed strategically and the weight of the building transferred on to them by the reinforced beam.
Mass Concrete Underpinning
Concrete underpinning increases the mass of the foundation to strengthen it. Extensive excavation is done around or under and then concrete is poured strategically. The method is applied where the existing foundation lies at a shallow depth. It is a simple and cheap method that does not require use of heavy machinery though it can be a slow process. Also, the building can still be used while renovations are being done.
Expanding resin injection underpinning
This underpinning method is fast, least invasive and does not involve excavation. A mixture of hardener and resin is injected into the ground. The mixture expands and fills any spaces or cracks and also compacts loose soil. The process may even raise sunken parts of a building. Resin injection is a simpler and less expensive method.
Whatever method you choose to use will have varying costs depending on a number of factors, which include the following:
- Location of the building
- The type of footings in the foundation
- Soil type
- Accessibility of the foundation
- Amount of materials required