The soil beneath our feet is constantly shifting and changing. This can cause problems for buildings, especially those with shallow foundations. Reactive clay soils are particularly prone to expanding or contracting depending on the moisture content. If there’s more moisture present – like when there’s leakage next to the footing – the clay swells and causes the footing to heave. Less moisture – like when there are trees close to the footing– results in soil shrinkage, which then causes the footing to settle. This can lead to significant building distortions, deflections, deformations, and uneven floors which can be unacceptable. Several methods have been around for fixing the problem, one of which is the resin injection ground engineering method.
Resin Injection is a process used to stabilize buildings and pavements
Resin Injection is a process used to stabilize buildings and pavements that have shifted due to differential settlement. This method does not require excavation or the installation of additional structural elements (i.e. underpins), making it a popular choice among homeowners. However, there has been much controversy surrounding this method, particularly among engineers. While resin injection has proven to be quite effective for mitigating liquefaction beneath existing structures caused by an earthquake, its long-term effectiveness and performance for shallow-founded residential houses experiencing differential settlement on reactive soils are still questionable.
Resin injection can be a viable solution or just a short-term fix to a bigger problem
Resin injection has been widely used in Australia since the 1990s as a quick and easy solution to address foundation issues on reactive soil, often without consulting a structural engineer. However, this method doesn’t always produce the desired results, and there has been much debate in recent years over whether this is a viable solution or whether it is just a short-term fix to a bigger problem.
This article will explore whether resin injection ground engineering is a viable option for re-levelling a residential house. We’ll look at the pros and cons of this method to help you decide if it is the right choice for your project.
What is resin injection ground engineering?
In civil engineering, grouting is the process of injecting pumpable materials into a soil or rock formation to change its physical characteristics. This technique has been used since 1800, when it was first employed to repair a sluice in Dieppe, France. Since then, it has been successfully used to fix dams and other structures. In 1950, the process of compaction grouting was introduced. This involved using a zero-slump grout made of cement, sand, and water to compress any weak materials in a foundation. After remedying many buildings damaged by the Newcastle earthquakes in 1989, the idea arose to use this solution to re-level sunken slabs and footings.
Although there are many different types of grout for lifting slabs and footings, the most popular one is polyurethane (PU) resin. Polyurethane (PU) resin is a common material used for grouting due to its science-backed ability to quickly and effectively expand when mixed with water and fill in gaps underneath the slab or footing with a foam-like substance. The expansion pressure from the PU resin also compacts the surrounding soil, increasing its bearing resistance. Injecting PU resin beneath a structure can also help to lift it and remediate settlement without having to excavate.
Advantages of resin injection ground engineering
When it comes to raising and re-levelling a footing, there are a few different options to explore. Structural engineers often recommend conventional underpinning, which involves excavating around the foundation and installing support piers. However, this can be disruptive and destructive, taking days or even weeks to complete. With resin injection, however, there is no excavation or heavy machinery required. As a result, the process is much faster, typically taking less than two days, and causes far less disruption.
Also, underpinning historical and heritage houses built on significantly shallow founded bluestone footings is difficult and sometimes even impossible. In some cases, the only viable option may be to inject resin into the foundation and structure. The resin injection ground engineering method can provide the stability needed to preserve these important historic buildings.
Disadvantages of resin injection ground engineering
Resin injection ground engineering is not always the best solution for remediation and improving the foundation soil below footings and can actually make the problem worse. In some cases, it has made little to no difference in floor levels and differential movements of the house.
Read a case study on failed attempt at resin injection ground engineering works here
It is important to note that injecting resin below the footings will not prevent further movement if the foundation soil is continually exposed to moisture fluctuations. Therefore, it is crucial to first address the underlying issues causing the building movements/settlement before proceeding with any ground engineering works. Attempting ground engineering works without addressing the root cause of the problem is likely to be ineffective. It may even further complicate and reduce the likelihood of success for future foundation/footing remediation works.
Furthermore, differential movements of the footings and subsequent damage to the house can become significantly pronounced if the foundation soil has become more stabilized due to resin injection compared to the areas of the house where the footing is still founded on reactive soil.
Finally, resin injection may be less intrusive than traditional underpinning, but it is not always as non-destructive as you may believe. For example, if subfloor access is insufficient and the injection must be done from inside the house, holes must be drilled into the internal flooring – which can leave permanent marks or, worse yet, break older tiles. This can significantly add to the initial quoted cost that most homeowners do not consider before committing to resin injections.
Should you consider ground engineering to fix the foundation of your house?
Every site presents its own unique challenges. Reactive soils are particularly troublesome, as they can cause cosmetic damage to houses even though the underlying structure may be sound. A structural engineering assessment is required to investigate the cause of the damage and identify an appropriate treatment plan. A competent Forensic engineer must do an in-depth risk vs benefit analysis of underpinning and resin injection options before recommending it as the best course of action. In many cases, the best course of action may be as simple as stabilizing moisture conditions or replenishing moisture in dry foundations rather than undertaking major structural repairs.
In summary, before choosing to proceed with resin injection ground engineering, it is important to consult with a reputable Forensic Structural Engineer. Keep in mind that once the work is done, there’s no going back, and resin injection companies don’t usually guarantee results. So, it is essential to get professional input before making a decision.