A Case Study on the Evaluation of Soil-Cement Stabilization for Gravel Road Subgrades in the State of Tennessee: Laboratory Testing and Field Recommendations

Cement stabilization is a widely applied method for improving the mechanical performance of unpaved road subgrades, aiming to increase soil strength, stiffness, and durability under traffic and environmental stresses. This study presents a detailed case investigation of subgrade stabilization for gravel access roads at a 1,200-acre site along Lynchburg Highway in Tullahoma, Tennessee. The project encountered subgrade instability during grading, prompting a comprehensive laboratory testing and geotechnical evaluation program. Representative soil samples were collected from eight locations at depths of 0.5–1.5 ft below the surface and tested with cement contents of 6%, 8%, and 10% by dry weight. Laboratory procedures included Atterberg limits, moisture content, standard Proctor compaction, and unconfined compressive strength (UCS) testing after seven days of molding and curing the samples.The results indicated that none of the soil–cement mixtures achieved the target minimum 7-day UCS of 100 psi, a criterion established by the Tennessee Department of Transportation for acceptable chemical subgrade stabilization. Reduced strength values were attributed to challenges in achieving homogeneous mixing and controlling moisture content for clayey soils in field conditions. Based on these findings, cement stabilization was deemed unsuitable for the site soils, and other stabilization methods such as lime stabilization and geogrid reinforcement of road subgrade were recommended as a more effective alternative. Practical recommendations for subgrade treatment, including proper scarification, chemical application, mixing, compaction, and curing procedures, are provided to ensure long-term stability of aggregate-surfaced roadways. This study highlights the critical influence of soil properties, cement dosage, and field construction practices on stabilization performance and provides site-specific guidelines for improving subgrade reliability in low-volume gravel road applications.