Test Procedure for Determining Organic Matter Content in Soils -- UV-VIS Method (5-5540-01-P4)

The Texas Department of Transportation has been having problems with organic matter in soils that they stabilize for use as subgrade layers in road construction. The organic matter reduces the effectiveness of common soil additives (lime/cement) in stabilization projects. The researchers developed a technique using UV-Vis spectroscopy to measure the harmful organic matter in another project (0-5540). This project consisted of purchasing three UV-Vis instruments, equipping them with software to measure the organic matter and doing two trainings with the Texas Department of Transportation. Following the trainings, four laboratories analyzed 20 natural soil samples and three laboratory standards to determine repeatability and reproducibility between the laboratories. Researchers also continued testing real project soils to see what mitigation techniques researchers could use. Researchers determined that three replicates need to be run to achieve 95 percent confidence that the measured value is the true value. Researchers determined that soils with organic matter below 1.5 percent can be safely treated, and soils with an organic matter to Eades & Grim optimum lime (OM:EG) ratio less than 0.5 have the greatest potential for mitigation with additional lime application. Additionally, calcium chloride added to the soil with the lime improved the formation of pozzolanic reaction products and strengths of some soils. This work illustrates the complex nature of organic interactions with soil stabilizers and the many questions left unresolved.