Geopolymer injection vs underpinning and piling – What is the right treatment for sinking floors and subsidence in warehouses and commercial buildings?

When a warehouse or a commercial building is suffering from sinking floors and subsidence, the business concerned will look for the most appropriate method of treatment that can resolve the problem in a way that keeps disruption to its employees, customers and the business overall to a minimum and in the most economical way possible.

To make the most informed decision, it is important to commission a ground investigation survey upon which to base the choice of treatment. The survey can look at a variety of points. It can establish soil composition, the load-bearing capacity of the ground, the impact of the volume of water in the soil and the depth and condition of the existing foundations and the slab. These are vital to being able to narrow down which of the subsidence treatments available – underpinning, piling, or a more modern method, geopolymer resin injection – is the most suitable option.

The most appropriate treatments will vary from project to project. No one subsidence treatment solution can be said to be the silver bullet and the only choice for every situation. All the factors determined by the ground survey must be considered. These may rule out the use of techniques that would otherwise be specified based purely on basic assumptions about building loadings and depth of foundations and expected soil conditions.

Once the choice of viable subsidence treatments is established, the impact of each method on the running of the business during its implementation can be assessed. This will enable the selection of a solution that balances the business needs, the level and duration of disruption and remedial actions required following the completion of the work with the benefits of the treatment itself.

The following findings from the soil investigation report all need to be considered when checking the viability of one subsidence treatment method over another.

The type of soil below the foundations of warehouses and commercial buildings will affect its load bearing capacity. Very poor soils can prove difficult for all types of subsidence techniques to overcome. However, the nature of geopolymer injection is that the resin will fill voids, expand and compact the soil. This is not an option available for mass concrete methods, although deep piling may be viable if stronger ground can be found deeper down below the foundations.

If foundations are shallow, where the depth of the foundations is no more than three times their width, then both traditional underpinning methods such as mass concrete underpinning and more modern techniques that use geopolymer resin technology are applicable. Geopolymer resins have the advantage of being easily applied through injection tubes at various positions across the site. These are small bore tubes, typically 16mm in diameter, driven into the ground through holes pre-drilled under the foundations, or directly through concrete slabs, by handheld equipment. These include under central areas of, for example, sunken concrete slabs, where excavating the trenches required for mass concreting would be problematic.

Where ground strengthening is needed under deep foundations this favours the use of piling to remedy the subsidence. The piles can be driven deep underground to transfer the weight of the foundations to a competent load bearing soil strata. However, depending on the load-bearing capacity of the ground, geopolymer injections deeper into the ground may also be applicable in some instances. There is also the option of combining the two types of solution to complement each other in some cases. In general, warehouses and many commercial buildings are unlikely to have deep foundations, however, the ground survey will reveal this and may show that one, or both, of either piling or geopolymer injection, are suitable.

The height of the groundwater level on a site will depend on many factors including geology, climate, the influence of rivers and waterways as well as local drainage provision. It is an important consideration when selecting subsidence treatments.

Ground that is more prone to flooding can make it more difficult and time-consuming to employ traditional techniques that involve working under the water table when excavating trenches and boreholes. The geopolymers used for injection into the ground are hydrophobic so can be used with confidence where water has been identified as an issue by the ground investigation report.

Once conclusions have been drawn based upon the findings of the ground investigation survey, there are other factors that may be relevant when a business makes its final decision to use a particular method of subsidence treatment.

The location, position and surrounding infrastructure of a site will determine how easy it is to access. Access can be an issue for some of the heavy machinery required by more traditional subsidence treatments. Where piling is concerned heavy plant will be utilised and access to vehicles to remove the spoil from any excavations may be required for both mass concreting and piling operations.

By contrast, geopolymer resin injection technology produces no spoil and is carried out with handheld machinery. This allows easy access to be gained both outside or, where required, inside warehouses and commercial buildings to carry out the work needed to arrest the subsidence to concrete slabs or foundations.

This is linked to the access issue, as methods needing machinery, excavations, and delivery of concrete to site will add to the disruption felt by the business. Health and safety will need to be addressed with all this additional activity from contractors and equipment. Decisions will need to be made to see if all the business is safe to remain open during the works or whether parts of it will have to be closed.

Geopolymer injection technology is unobtrusive and in most cases any disruption is so minimal that businesses can remain fully open throughout the subsidence treatment process, allowing revenue to continue to be generated.

For some businesses where the environmental impacts of their actions are measured, tracked and reported, the impact on the embodied carbon of any process undertaken will be a factor in the decision-making process. It is well documented that the cement used in concrete creates 7% of the world’s CO2 emissions and subsidence treatment processes such as mass concrete and piling using this material will increase the overall embodied carbon of the warehouse or commercial building they are treating. The energy used by any machinery required for the processes will also introduce additional carbon emissions.

Low-carbon concrete is a relatively new product in the market and this can be explored as a way to reduce carbon although this will add cost to traditional subsidence treatments.

Teretek geopolymer injection uses resins that are not based on cement production and their application uses handheld equipment with limited energy use compared to that required by many other alternative methods. The lower embodied carbon impact of geopolymer injection compared to underpinning and piling may therefore make it a more sustainable choice for some businesses.

Another technique for treating subsidence is JOG Computer Controlled Grouting. This uses a cementitious grout precisely injected at multiple points around a building and is able to correct for level as well as treat subsidence. Although this technology is based on cementitious material the highly accurate computer controlled delivery of the grout means that, when compared to traditional concrete underpinning methods, far less cement is needed and therefore less embodied carbon is added to the building.

Armed with your ground investigation report, if you contact our team at Mainmark, we can help you get a thorough and comprehensive picture of the options available to you.

If we feel that traditional underpinning and piling treatments are the best option, we will tell you. However, if your subsidence can be treated with all the advantages of modern geopolymer injection technology, offered by our Teretek® system, we will tell you that too. It is a proven technique that has shown its worth for many businesses where they have been able to continue trading throughout the process of treating subsidence. It’s a quick effective and non-intrusive way to get your warehouse or commercial property and business back on a level footing.

For more information and an expert opinion on the options available to you to solve your subsidence concerns please contact our team of ground engineering specialists. We’d love to help.