Advanced Soil Strengthening and Stabilization

Opportunity

Application

Humans throughout history have been attempting to stabilize the ground beneath them as the demand for construction and development around the world has steadily increased. Often soil needs to be stabilized for construction purposes, such as the construction of new buildings and roadways. However, it can also be beneficial to stabilize soil for other purposes as well, such as increasing sand’s resistance to erosion and scour or because of issues associated with creep or settlement. Unfortunately, most existing solutions are expensive, limited in effectiveness, and/or unsafe to people or the environment.

Surfactant-Induced Soil Strengthening provides significant advantages over these older solutions. It is inexpensive and easy to apply, and testing shows it to be very effective for strengthening and stabilizing a wide range of soil types. Depending on matrix and application rate, the invention can more than triple the unconfined compression strength of soils.

Invention Details

Often when large-scale engineering structures like buildings, bridges, or roadways are built, soil improvement is required to stabilize the subsurface. Several technologies are available for this: grouting, concrete and/or cement injection, cutting/replacing, surcharging, etc. Each of these techniques has its own set of advantages and disadvantages, but overall, most existing technologies for soil stabilization are expensive and/or harmful to the environment. In recent years, a new method for soil stabilization has been developed whereby naturally occurring microbes are used to drive chemical reactions that ultimately lead to precipitation of calcium carbonate, and the calcium carbonate strengthens soil. This soil stabilization method is sustainable and uses relatively simple ingredients: naturally-occurring bacteria, a calcium source (usually calcium chloride which is a common salt), and urea. Results in sands and granular soils have been promising.

Starting in 2015, UNF researchers began attempting to apply geomicrobial soil improvement in soil with high organic content because these soils remain a significant challenge for roadway construction in Florida. The UNF team tried (and repeatedly failed) to make this work using various techniques. At one point in the investigation, researchers hypothesized that maybe the reason geomicrobial soil improvement techniques were failing in the organic soil was due to particle surface charges in the sense that silica sand is a dipole similar to water while organic materials are generally neutrally charged. In an effort to mimic the silica’s dipolar behavior, anionic surfactants, the active ingredient in most shampoos and soaps, were added to the geomicrobial improvement recipe. The result was organic specimens that appeared to harden. But, upon further investigation, the research team realized that this hardening was not due to the geomicrobial chemical processes. Rather, the observed hardening was attributable to the surfactant bonding to calcium ions from the calcium chloride. A new soil stabilization method was born!

When the UNF team thought about what had happened further, they realized that the calcium from the calcium chloride had made “hard water.” As anyone with hard water knows, its alkali metals (i.e., calcium, magnesium, etc.) bond to soaps to create an insoluble substance that builds in pipes. While this is terrible for homeowners with hard water, it turns out that the same mechanism is great for strengthening soil!

UNF investigators ran a series of experiments to optimize this new soil stabilization technology and dubbed it “Surfactant-Induced Soil Strengthening” (SISS). The resultant optimized specimens showed significant strength improvement. In addition, this technology appears to be applicable to a wide range of soil-types including sands, clays, and soil with high organic content. As a “bonus,” experiments showed that in the presence of saltwater, ion exchanging tends to breakdown the SISS strengthening matrix. This means that the technology could be used to temporarily stabilize a beach or dune (for example, to prepare for an impending hurricane); provide improved protection when compared to an untreated shoreline; and over time, the beach or dune would return to its untreated state simply because it is continually exposed to saltwater. As such, it may be possible to upscale this technology and use it as a temporary protection technique for coastal structures vulnerable to hurricane erosion while simultaneously allowing for a return to sandy beaches after the storm has passed.

US Patent 11,274,251. Invented by Dr. Raphael Crowley, Taylor Engineering Research Institute, School of Engineering with Matt Davies, Nick Hudyma, and Josh Sasser