INVESTIGATION of EFFECTS of RAYLEIGH WAVE DIFFERENT MODES on DISPERSION CHARACTERISTICS of LAYERED MEDIA
Surface wave method is a new nondestructive testing procedure used for in-situ evaluation of elastic moduli and layers thicknesses of layered structures, such as soil sites and pavement systems. The method is based on the dispersive characteristics of surface waves in layered media. The impact source used in the surface wave method usually generates Rayleigh waves with different frequencies, therefore the obtained experimental dispersion curve contain various modes specifications. In this paper, the effects of propagation of different modes of Rayleigh wave on the dispersion characteristics of layered media determined from surface wave method is studied and investigated. For this purpose, the Thomson – Haskell formulation is employed in order to construct the dispersion curves of different modes of Rayleigh waves, and the corresponding software is designed and developed to determine and plot the first mode and higher modes of Rayleigh wave dispersion curves. The effects of propagation of Rayleigh wave different modes on these characteristics are evaluated using the medium response of different modes. The results show that the transmitted energy into the system by the fundamental mode is much higher than the other modes. Therefore, the theoretical dispersion curve obtained using the fundamental mode can be used with acceptable accuracy to make the inversion process in order to determine the stiffness profile of the system.