Stabilization of Soft Clay Subgrades in Virginia: Phase I Laboratory Study
Christopher M. Geiman
Filz, George M.
Thomas L. Brandon
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Many pavement subgrades in Virginia consist of wet, highly plastic clay or other troublesome soils. Such soils can be treated with traditional lime and cement stabilization methods. Alternatives, including lignosulfonates and polymers, are available, but their performance record is mixed and solid engineering data are lacking, which prevents reliable design. The goal of this research was to screen a suite of traditional and non-traditional stabilizers against three Virginia soils that have caused problems during construction or resulted in poor performance in service. The selected stabilizers were: quicklime, hydrated lime, pelletized lime, cement, lignosulfonate, synthetic polymer, magnesium chloride, and a proprietary cementitious stabilizer. A laboratory procedure was developed and applied to three Virginia soils obtained from Northern Virginia, Staunton, and Lynchburg. Key findings from the research include: (1) traditional lime and cement stabilizers were far more effective than liquid stabilizers (lignosulfonate, synthetic polymer, and magnesium chloride) in increasing strength; (2) the liquid stabilizers were ineffective on soils with a high moisture content; (3) the proprietary cementitious stabilizer was more effective in increasing strength than lime for all cases tested but not was not as effective as the cement stabilizer; (4) quicklime and hydrated lime increased the workability of the soils although they did not produce strengths comparable to cement; (5) the strength of soils stabilized with cement and the proprietary cementitious stabilizer can be estimated based on the water-amendment ratio of the mixture; and (6) the strength of soils stabilized with lime can be estimated based on a combination of the plasticity index and the water-amendment ratio of the mixture. The benefits of subgrade stabilization are that it improves the strength, stiffness, and durability of soft subgrade soils. Such improvement allows a reduction in the required thickness of overlying pavement courses and/or an increase in pavement life. Quantifying the life cycle cost benefits requires performing pavement design studies based on anticipated traffic levels, desired serviceability, etc. The preferred design method would be a mechanistic design, which requires resilient modulus values for the stabilized subgrade and other pavement layers. Neither resilient modulus testing nor pavement design studies were included in the scope of the work for this project, but they should be included in subsequent phases.