What is Underpinning?
Underpinning is the process of strengthening the foundation of an existing building or other structure. It typically involves extending the foundation depth or distributing the load across a greater area. Most of the time, underpinning is a major repair project. In order to choose the correct method, you need to understand the current situation and any problems concerning the entire foundation.
Why is Underpinning Necessary?
There are a variety of reasons why your home might require underpinning. Many times, it is related to subsidence issues. Some examples of why underpinning might be necessary are:
- A change in soil conditions under the foundation
- Soil characteristics were not properly taken into account during the design phase
- The original foundation is no longer suitable/strong enough
- The construction/repair/excavation of neighboring structures endangers the current foundations
- Additional floors are to be constructed underground
Types of Underpinning
There are a few different methods of underpinning that are commonly used to underpin a house or any other type of building.
Mass Concrete Underpinning
Mass concrete underpinning is a traditional method of underpinning where the soil under the foundations is replaced. The process begins by digging out the soil. Then, concrete is poured to replace it. The soil is often replaced in squares based on a sequence determined by an engineer. This ensures the bearing capacity of the current foundation is not compromised. The result is a stronger foundation built underneath the existing one. This method can be used for shallow foundations. It's best used when the current structure is strong enough to span over the underpinning pits.
A piled underpinning is used when firm soil layers are situated at substantial depths and the soil above is inadequate to bear the loads. Piled underpinning is best when there is limited access to the construction site. It can also be ideal for situation where there are environmental concerns regarding excavated soil or a need to minimize movement during the process. The piles are usually steel-cased and can be filled with concrete. There are three types of installation techniques commonly used: driven piles, drilled piles and jacked piles. Piling methods require load transfer structures to transfer loads from the existing foundations to the piles.
Jet grouting is the creation of a geometric pattern of grouted soil under the foundation. This method uses a high-velocity jet of cement grout (with or without water/air). In underpinning applications, jet grouting is typically used to create columns of grouted soil underneath an existing foundation. The end result depends on soil characteristics, especially erodibility. Generally, jet grouting is effective across a wide range of soil types. Load transfer structures are not needed, because the columns can be extended to the existing foundation in many cases. Because of the required drilling and high pressure used, jet grouting always causes a soil disturbance, making it unsuitable for very sensitive foundations. The construction site must also be accessible to heavy equipment.
This is the underpinning solution used by Geobear. Over the years, geopolymers have been used for a number of geotechnical applications, such as the stabilizing and re-levelling of floors, compaction of granular soils, or increasing the bearing capacity of foundation soils for existing structures. Geopolymers are based on multi-component structural, expanding resins and they are environmentally neutral and water-resistant. The technique is based on chemical expansion pressure, instead of heavy pressurized hydraulic systems, which makes the application more controllable and safe.
Compared to traditional materials like cement, geopolymers have an effective and structurally strong curing process. They achieve 90% of the final compressive strength in less than 15 minutes. Most projects can be completed in days - even in cases where traditional ground repair methods would require weeks or months to finish. Unlike traditional underpinning techniques, geopolymer solutions are excavation free. As they utilize small and light installation machinery, these solutions result in fast and non-disruptive solutions for most buildings.
Challenges with Traditional Underpinning
The greatest challenge with traditional underpinning is the length of time it takes and the mess it creates in and around a home. Because traditional methods require excavation and digging beneath the property, they can be highly disruptive to your day-to-day life. When compared to Geobear’s geopolymer method, which only takes 1-2 days, traditional styles of underpinning are becoming a last resort for property owners.
Ask Geobear for Help
With the Geobear method of foundation underpinning, there is no reason to leave a property and there is absolutely no excavation or digging – we just need a way to get our material beneath existing foundations, which requires drilling a pattern of small holes around the affected area. At Geobear, we have been working around the world for over 30 years on thousands of properties using our ground injection method as a more convenient alternative to those traditional methods. Contact us below to learn more!