In-Situ Investigation using SH-Waves

The in-situ dynamic shear modulus of pavement materials may be deduced from measurements of the surface phase velocity of horizontally polarized shear waves (SH-waves). The velocity of SH-waves as observed at the surface of layered pavements is dependent on the frequency of wave motion, the material properties and the layer thicknesses. Interpretation of the observed phase velocity dispersion with frequency allows the material properties to be obtained. A torsional vibrator capable of generating continuous SH-waves at the surface of a pavement, and instruments suitable for detecting and measuring the velocity of the resulting wave motion, are described. This equipment was used to obtain dispersion plots on two- and three-layer pavements. Theoretical phase velocity-frequency dispersion relationships are presented, describing the propagation of SH-waves in idealized two- and three-layered pavement-type structures. The observed dispersion plots were interpreted, using theoretical dispersion relationships for comparable idealized structures, to deduce the material properties.