STRUCTURAL SUPPORT OF LIME OR CEMENT STABILIZED SUBGRADE USED WITH FLEXIBLE PAVEMENTS

Lime or cement stabilizations have been used to modify wet and soft roadbed soils so that the roadbed can carry the load of construction vehicles without excessive rutting. Lime stabilization is recommended for fine-grained and high plasticity soils, and cement stabilization is recommended for coarse-grained and low plasticity soils. The durability and structural benefits of the stabilized road bed soils have been investigated in this study through four tasks. First, the in-situ conditions of stabilized subgrade were investigated using the Dynamic Cone Penetrometer (DCP) test. The results show that the moduli of stabilized soils are generally higher than non-stabilized soils several years after construction. The second task investigated the durability and strength characteristics of stabilized soils through laboratory tests. Unconfined compressive strength, California Bearing Ratio, and resilient modulus of stabilized soils are all higher than non-stabilized soils. After freezing and thawing cycles, the stabilized soils retain more strength and modulus than the non-stabilized soils. The third task evaluated the conditions of 4 test sections on State Route 2 in Erie County, with subgrade stabilized with 6% cement, 5% lime, 3% lime with 3% cement, respectively, and a control section with no stabilization. Pavement deflection measurements were taken during different stages of construction and for each of the 3 years after construction. The backcalculated subgrade moduli show that stabilization increases the subgrade modulus, with the cement treated soil being the strongest initially, followed by the 3% lime plus 3% cement section. However, the lime stabilized subgrade continues to gain strength three years after construction. The cement stabilized section has sandy soils, while the other sections have clayey soils. The fourth task developed a design procedure to quantify the increase in strength and modulus as an "effective" subgrade modulus in order to include the structural benefit of stabilized subgrade in the current pavement thickness design procedure.