CHARACTERIZATION OF MOISTURE-DEPENDENT CHANGES IN STIFFNESS OF UNBOUND AGGREGATE BASE MATERIALS IN FLORIDA

摘要

The Mechanistic-Empirical Pavement Design Guidelines (MEPDG) recommend use of materialmodulus in lieu of structural number for pavement base layer thickness design. Modulus isnonlinear with respect to effective confinement stress, loading strain, and moisture (suction), andmodulus nonlinearity should be considered for an efficient base layer design and analysis. Fixed7free resonant column tests were conducted on two base materials used in the State of Florida tocharacterize shear modulus (G) nonlinearity in the strain range of 10~(-5)% to 10~(-1)%, includingsmall-level strains, under different loading confinements and moisture contents. The suctioneffect on nonlinear modulus due to drying was evaluated, and it was found that unsaturatedmodulus is linear at strains lower than 10~(-5)% and nonlinear thereafter. Compared to drymaterials, the presence of moisture in unsaturated material makes it more nonlinear with respectto strain. The suction effect increases G in the strain range of 10~(-5)% to 10~(-1)%, with verysignificant increases at strain levels below 10~(-3)%. Empirical equations were developed tocalculate very small-strain modulus (Gmax) of dry material. A procedure to calculate anapproximate G value at known moisture content, confinement, and strain magnitude wasdeveloped.