Using Seismic Moduli in Structural Design of Flexible Pavements

In many current procedures for structural design of pavements, an accurate determination of layer moduli is required. With the onset of the movement toward the 2002 Mechanistic Pavement Design, investigating the feasibility of supplanting the existing methods with more mechanistic approaches would be desirable. Nondestructive testing techniques are widely used to determine moduli of pavements, the critical strains and, thus, to estimate the remaining lives of pavement systems. A nondestructive testing device, the Seismic Pavement Analyzer (SPA), whose operating principle is based on generating and detecting seismic waves in a layered medium can be used for this purpose. Seismic methods provide fundamentally-correct linear-elastic moduli of different layers. To incorporate in pavement design and analysis, seismic moduli of different layers have to be adjusted to represent moduli at strain and stress levels that are close to those applied by truck traffic. To do so, the nonlinear and viscoelastic behaviors of different layers should be accurately determined. In this paper the process of using seismic data and laboratory tests to determine design modulus values and an attempt to validate this process are presented. Also included is a validation of the results based on FWD measurements.