When is Polyurethane Grout Rehabilitation an Effective Option?

The use of polyurethane grout injection for soil densification and structural rehabilitation has been revolutionizing the way public works managers and building managers think about rehabilitation vs. replacement. Due to cost-effectiveness and innovations in polyurethane injection techniques, the viability of the solution has been “fast expanding” and the applications are spanning across a variety of uses, such as roadway lifting, manhole and joint sealing, dam seepage barriers, seawall stabilization, and building foundation realignment.

The question is, when does polyurethane grout make sense as a rehabilitation solution?

As you can imagine, this question is filled with a ton of variables, but we will point out typical rehabilitation opportunities and questions you should ask yourself around overall viability.

1. Is the issue repairable via polyurethane injection?

The first thing to consider with this question is “Is the issue soil related?” First and foremost, polyurethane injection is used to fill voids, whether large voids where no soil is present, or voids that exist between unconsolidated soils. The polymer is fast expanding, so once the voids are filled the polymer then compresses and densifies the soil and increases its weight-bearing capacity. So if your problem is being caused by weak or weakening soils, then polyurethane may be an excellent solution.

2. What is the condition of the structure being rehabilitated and what are your goals?

While we obviously think polyurethane injection is pretty great, the fact is, it isn’t a silver bullet. If the intended use of the structure is for continued use, the structure ought to be in a relatively operable condition. While we have been able to do amazing things with brick manholes that have lost grout, we are mainly focused on ensuring the structure can still meet current demands by rehabilitating the soil around or underneath the structure. But if the structure is crumbling or there is a focus on having the structure meet considerable volume increases, rehabilitation may not be a solution.

3. When considering sewer infrastructure, when is polyurethane applicable?

Polyurethane injection is highly adaptable when it comes to pipe and manhole joint rehabilitation. The reason is the application can be performed from inside the structure (access permitting) or from the surface.  The polymer is ideal for sealing leaking joints or stabilizing the structure.  Once injected, the polymer aggressively expands throughout the voids, sealing joints against Inflow and infiltration. In addition to sealing joints and filling voids, the polymer stabilizes the adjacent soil providing increased support for the structure and preventing future washout of the stabilized soil.

As mentioned in item #2, the condition of the structure and its future requirements are a consideration when determining whether polyurethane injection is a viable rehabilitation option. That being said, groundwater leakage and inflow and infiltration can be a major cause of sanitary sewer overflows and, if mitigated, can result in better utilization of your actual wastewater flows and you may find your current designs to be more adequate than thought.

4. Can polyurethane injection be used to increase soil load bearing capacity to handle heavier loads?

In short the answer is yes, but it really depends on how much weight, the soil quality, and the nature of the geology and subsurface structures. There are several instances where we have helped repurpose foundations to handle dramatically increased loads, such as silos, cranes, heavy equipment and machinery, and structural support columns. In each instance, the injection approach was uniquely designed to take advantage of the current soil and geological makeup of the site.

Not every site is capable of load bearing increases.  In sites with highly plastic soils, the polyurethane’s bearing increase becomes limited to the bearing capacity of polyurethane itself as it is unable to permeate the soil and cannot build structural integrity by mixing with the soils. In order for ideal bearing-capacity increase, the ability for the polymer to saturate and bind the soil into a contiguous structural layer must be available.  The injection design can help develop a bridging technique to help distribute the loads more evenly over the newly strengthened soil.

Conclusion

Polyurethane is an excellent rehabilitation solution when structural circumstances permit and financial conditions make sense. When determining these issues, we recommend running an ROI analysis, developing a rehabilitation solution with a Ground Works Solutions representative, and having an injection approach designed which would meet your project goals.
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