When considering the use of chemical grouts to stabilize shallow soils, several criteria must beconsidered for the selection of an effective chemical grouting program. Current industry standard has adopted a one-size-fits-all mentality; however NEC Keystone approaches the remediation process holistically. We believe that the use of chemical grouts should be tailored to each unique soil condition – providing the owner with the most efficient and durable solution.
Prior to choosing a shallow soil stabilization program, it is necessary to have a basic understanding of the available materials and their uncured and cured properties. While there are thousands of chemical grouts available today, we focus on the two main types of chemical grouting commonly used: Single-part permeation grout and Two-part polyurethane grout.
Single-part permeation grouting is a procedure that utilizes a low-viscosity, polyurethane resin to encapsulate loose soils, fill voids and form a water-tight barrier. This process has been utilized for many decades to achieve subsurface improvements. As such, there are many studies and scholarly articles available that detail the use of this material. An important aspect of permeation grouting is the relatively low injection pressures, combined with a minimal amount of curing expansion, allowing the product to permeate into the existing voids of the soil matrix without disturbing or altering the soil unit. Through the use of chemical additives, curing time can be shortened or extended to maximize the benefits to the existing soils. Permeation grouting is a very controlled process that permits precise documentation of subsurface improvements, such as soil stabilization, water cut off, encapsulating hazardous materials, stabilization of underground utilities, dike, levee and seawall repairs and stabilization of pools and other light structures.
Two-part polyurethane grouting is a procedure used for filling voids and obtaining densification of soils by means of soil displacement. Two-part polyurethane injection has become the industry standard used worldwide for the past 20 years for densification under concrete structures and roadways while lifting and realigning. Two-part polyurethane injection occurs under higher pressures and the material expands rapidly to fill voids and displace soil. This product must be used beneath structures or roadways in order to have something to push against to create the necessary compression for complete remediation. The most important aspect of Two-part polyurethane grouting is that it only displaces soil – it does not stabilize the soils as in Single-part permeation grouting.
Which Solution Is Right for My Repair?
Both the Single-part and Two-part polyurethane solutions are excellent in their individual applications, but neither should be specified in all soil conditions or for all desired outcomes.
The condition of the subsurface soils and the desired project goals will determine which process will give the best outcome. There are also many circumstances where a combined approach would be best suited for stabilizing deeper zones through permeation grouting and then lifting/leveling structures with Two-part polyurethane injection at the soil-to-concrete interface.