To understand the science behind the injection mitigation process, it's helpful to explore what the term stabilization refers to and its significance in our development throughout history.
Soil stabilization, also known as chemical injection, is a term for the act of altering or rendering the soil strength to better handle load bearing requirements for the structure being built. Many articles and studies have been conducted on the variety of ways to achieve stabilized soils and a number of agents that can be utilized to mitigate the poor sub surface material.
We have record of early civilizations using methods of soil stabilizers from Egyptian, Greek and Roman time periods, as lime serving as the stabilizing agent. In the recent study from 2021, Effectiveness of Ionic Stabilization in the Mitigation of Soil Volume Change Behavior, the researchers state, "Studies on soil stabilization using ionic stabilizers for engineering purposes may date back to 1950's and 1960's. The early works on ionic stabilization widely involved the utilization of phosphatic and sulfuric acid. Phosphoric acid was firstly adopted as a stabilizer to improve soil strength by Michaels and Puzinauskas and Lyons. However, a literature review conducted by Sokolovich presented that the chemical soil stabilization using acids, i.e. phosphoric acid, was firstly proposed by Budnikov et al. Michaels and Puzinauskas highlighted the high effectiveness of adding 1% phosphorus pentoxide on the strength characteristics of an asphalt stabilized fine-grained soil. Michaels et al. showed that before adopting the phosphoric acid as a soil stabilizer, it was repeatedly used as a binder for ceramics and metal oxides.
This is imputed to the rapid cementation action and low
cost of the phosphoric acid. Michaels et al. also suggested that
some accelerator acid, such as sodium fluosilicate, can be utilized to accelerate the curing and strength gain, and increase the water resistance of phosphoric acid-stabilized soils.
Then, sulfuric acid was proposed by Hemwall and Scott to effectively participate with phosphoric acid in the ionic stabilization. Experimental results from Hemwall and Scott revealed that adding a certain amount of sulfuric acid would enhance the cementation of aluminum-phosphate in
phosphoric acid-treated soils, and thus greatly improve soil strength. Sokolovich postulated that phosphoric acid stabilizes the soils by invading the clay lattice, liberating the aluminum ion, and eventually forming a hydrogen bond."
Expansive clay has a tight bond with Silicon, Oxygen and Aluminum. This bond is where things are a problem. Its gives clay the ability to gain major swell with water, leading to excessive movement for the foundation slab as clay density and volume rise and fall with the wetting and drying.
The clay molecules are important to understand because of its lattice structure laying in tight compacted sheets, called tetrahedral sheets, giving it a great place to store water.
Our liquid stabilizing solution,
aka "the chemical", has a physical reaction with the clay's bond and structure. The solution wakes up an organic sulfonic acid (RSO3) that breaks the bond between Si-O-AL within these sheets and initiates another process that untangles the lattice that holds the clay together, permanently changing the subsoil. These liquid solutions are referred to as stabilizing solvent agents and our solution is a mix of 3 different acidic/sulfuric compounds.
All of this excitement is starting to build up, and we'll see how that plays out next...
Once the stabilizing liquid solution has saturated the clay, triggering a reaction process of breaking through the Si-O-Al bond, another process is charging up.
As the ions become active with all this activity, a process called ion cation exchange begins to occur.
Density of electrical charges in the clay drop as the amorphous silicon bond releases, forcing the expulsion of water out of the clay double layer sheeting. Positive charges from the stabilizing agent create the perfect attraction for the negative charged clay material to release the water trapped within.
Now that the injection mitigation has rendered the molecular bond, unwound the lattice structure, converted ionic charges and released this problematic water; we get to flow into the last function...
With the lattice structure opened, bonds released and water breaking free, the unstable particles begin to float freely within the chaos.
The final process is called particle flocculation and refers to the washing away of the larger particles as the smaller settle into porous subsoil materials.
Machine injection application requires such high-pressure water force to deliver the solution mix, it helps encourage flocculation movement with silt and runoff carrying away.
This is where it ends for expansive soil, rendered to stability and ready for it's testing bores to be drilled, following a
48-72 hour settling/drying period.