Guided wave propagation in three-layer pavement structures

A study on guided waves in a. layered half-space with large velocity contrasts and a decreasing velocity with depth is presented. Multiple mode dispersion curves are calculated in the complex wave number domain, taking into consideration the attenuation caused by leakage into the underlying half-space. The excitability of the modes by a vertical point force on the surface is also calculated. Results show that the measurable wave field at the surface of a pavement structure is dominated by leaky quasi-Lamb waves in the top and second layers. The fundamental antisymmetric mode of vibration is the dominating mode generated in the stiff top layer. This mode drives the complete system and continuity across the boundaries generates higher order modes in the embedded second layer. The interaction of leaky Lamb waves in the first two layers results in large variations in the excitability and the attenuation, so that only the waves corresponding to certain portions of the dispersion curves are measurable remote from the source at the pavement surface. It is concluded that these portions of dispersion curves can be individually resolved in practice, by using multichannel processing techniques. This holds the potential for a refined nondestructive testing technique for pavements. (C) 2004 Acoustical Society of America.