DYNAMIC LINEAR BACK-CALCULATION OF PAVEMENT MATERIAL PARAMETERS

The dynamic linear back calculation procedure for estimating pavement material properties is presented. Two approaches based on the fitting of the data in the time and frequency domain arc described in detail. The time-domain approach is recommended when the deflection histories do not decay to zero at the end of the sampling window. The parameter identification procedure used to generate the sensitivity matrix and the load vector and to solve the overdetermined set of equations is described. Twenty-four test sections from the GPS of the SHRP-LTPP program are analyzed. The material properties back calculated are: (1) The moduli of elasticity for unbound base, subbase and subgrade materials; and (2) the parameters of the generalized power law of the creep compliance of the asphalt concrete. The results are compared with those of the static linear back-calculation procedure and of laboratory tests. It is found that: (1) The moduli of elasticity for unbound materials from static and dynamic analyses compare relatively well; and (2) the exponents of the power law from back calculation and laboratory results do not compare well. It is suggested that the sample tested in the laboratory may not be representative of the whole asphalt concrete layer.