Calibration of Pavement Response Models for the Mechanistic-Empirical Pavement Design Method
Rong Luo and Jorge A. Prozzi, University of Texas at Austin, September 2007, 85 pp. (167264-1)
Most pavement design methodologies assume that the tire-pavement contact stress is equal to the tire inflation pressure and uniformly distributed over a circular contact area. However, tire-pavement contact area is not in a circular shape and the contact stress is neither uniform nor equal to the tire inflation pressure.
To precisely account for the effect of actual contact stress on pavement responses, this research evaluates pavement responses under the 3-D non-uniform stresses and under the uniform stress. The studied pavement responses include the horizontal strains at the pavement surface, the horizontal strains at the bottom of the asphalt layer, and the vertical strains at the top of subgrade. A multi-layer linear-elastic computer program, CIRCLY, is used to estimate pavement strains under a number of combinations of tire load, tire pressure, asphalt modulus, asphalt thickness and subgrade modulus. The Asphalt Institute method and the Shell method are used to predict the pavement fatigue life based on the critical strains at the bottom of the asphalt layer calculated by both 3-D stress model and the uniform stress model.
Results show that the vertical contact stress component of the 3-D stresses has the dominant effect on the studied pavement strains. The effects of longitudinal stress component and the transverse stress component cannot be ignored, especially for pavement with a thin asphalt layer. Asphalt thickness, asphalt modulus, tire load and tire pressure have significant effects on the differences in asphalt strains between the 3-D stress model and the uniform stress model, but not on the difference in the vertical strains at the subgrade top. Subgrade modulus shows little effect on the differences in all studied strains predicted by the 3-D stress model and the uniform stress model. Tire pressure has greater effect than tire load on the fatigue life of a pavement with a thin asphalt layer. When the pavement has a thick asphalt layer, the effect of tire load is greater than the effect of tire pressure, and a larger tire load is associated with a smaller number of load repetitions.
Keywords: Mechanistic-Empirical Design, Wheel Load, Tire Pressure, Pavement Response, Non-Uniform Contact Stress
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