Reasons and Methods of Underpinning
Underpinning services are essential to solidify and strengthen the foundation for any construction project. This is particularly important when:
- Soil conditions under the building have changed and are threatening the stability of the foundation.
- An existing structure's foundation is being used to build another building for economical reasons.
- The structure of the building has shifted due to geological activity such as earthquakes or other natural events including flood and droughts.
- Extra weight has to be put on the building, e.g., the purpose of the building has changed.
This process may be done by extending the width or length of the building's foundation to provide more support and increase stability by evening out load distribution.
Common Types of Underpinning
Mass Concrete Underpinning—This is a method that has been used for over 100 years. Basically, concrete is poured into trenches dug below the buildings foundation, creating a foundation underneath the existing foundation. This is a cost effective method of underpinning with low labour costs and little requirement for heavy machinery.
Beam and Base Underpinning—A beam of concrete is created below the existing foundation as a replacement for the existing footing. The purpose of this beam is to allow the load of the building to be transferred to concrete bases which are strategically placed across the foundation.
Mini-piled Underpinning—If the loads of a foundation need to be transferred a distance larger than 5 metres, this method of underpinning is the most suitable. Concrete piles linked by re-inforcement beams support the structure. This type of method is also used when an entire building needs to have its foundation stablilised.
Under-pinning Using Resin Injections
This is a fairly new method of underpinning, having been around for only about 30 years. In this method, a mixture of resins and hardener are injected beneath the foundation. A chemical reaction occurs between these two components underground, causing the resin to expand and fill any structural irregularities, such as crevices. The resin also helps to compact loose soil and hence is frequently used for building structures weakened owing to soil issues. This method is non-disruptive and time efficient; however, it is more expensive
The method selected for underpinning depends upon the type of building and the reasons behind underpinning. Professionals in the field assess the building and decide which method to use accordingly. Prior to this, it is important to get the soil tested by a geotechnical engineer to determine its type and level of stability.