Novel method for backcalculation of asphalt pavement moduli

There are many methods available for backcalculating pavement layer moduli. Because most use basin matching, they share similar drawbacks: the procedure may not converge, and the solution is probably not unique. Extensive calculations have revealed the existence of a point on the surface deflection basin, termed the "inertial point," whose deflection does not vary with the modulus of the upper layer. The relationship between the inertial point parameters and the structure information is established mathematically. The inertial point can be found directly from that relationship, and the subgrade modulus can be predicted as a by-product. Another important observation is that the surface course stiffness has a significant influence on the shape of the deflection basin near the loading center. From this observation, an iterative algorithm is developed to estimate the moduli of both the surface and base courses. The backcalculation method proposed will always obtain a unique solution because of the novel solution procedure used.