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This project summary report summarizes the research performed in Texas Department of Transportation (TxDOT) Project 0-5540. TxDOT has reported difficulty stabilizing with lime those soils bearing high and low concentrations of organic matter. Before a remediation technique can be developed, researchers have to understand exactly how the organic matter interferes with lime stabilization. The project had three objectives: to identify a good test to measure organic matter in soils and identify the fraction of organic matter that causes problems with lime stabilization, to determine what mechanism or mechanisms were responsible for organic matter interfering with lime stabilization, and to evaluate how organic matter affects the engineering properties of soils from real TxDOT projects. Researchers developed a quick field test to measure organic matter in soils and tested 146 Texas soils. Researchers found that the UV-Vis method for measuring organic matter is a good field technique that measures actual deleterious constituents. Humic acid, in concentrations greater than 1 percent, interferes with lime stabilization of soil by not allowing the lime to form the pozzolanic reaction products that generate long-term strength gain. Calcareous soils with high concentrations of organic matter (more than 1 percent) respond more favorably to lime treatment than acid soils. The natural soils show an increase in shrink/swell with increasing organic matter. With increasing organic matter, the natural soils stabilized with lime or cement exhibit a decrease in unconfined compressive strength (UCS) after 56 days of curing.