THE MODE AND SCATTERED ENERGY DISTRIBUTION OF GUIDED WAVES PROPAGATING IN TWO COUPLED PLANE-STRAIN LAYERS WITH RIGID BASE

The dynamic stability of subgrade in transition zones has become a key problem restricting the design of high-speed railway subgrade with a speed of 400 km/h and above. It urgent to explore the amplification mechanism of system dynamic response caused by non-uniform foundation from the perspective of wave and energy. In this paper, the foundation under track is reduced to a elastic layer which has a free surface and rigid bottom. The problem of vehicle induced elastic wave propagation in the transition zones in high-speed railway is refined into the problem of wave scattering in the inhomogeneous elastic layer with rigid base. A plane-strain model of two medium coupling elastic layers with rigid base is established. Facing with the dispersion equation of elastic layer with rigid base, the paper optimizes the method of finding roots in complex plane. Then, the dispersion analyses of the elastic layers that are assigned with geotechnical medium are carried out, and the corresponding multi-mode guided wave characteristics and the distribution of scattered energy are clarified. Furthermore, in terms of the thickness of elastic layer, stiffness ratio of two elastic layers and so on, comparative analyses are carried out at last. The results indicate that all of the guided wave modes in the elastic layer with rigid base have cut-off frequencies. When the thickness of the elastic layer decreases or the Young's modulus of the medium increases, the cut-off frequency of each order guided wave mode becomes higher. In scattering, the fundamental mode of the transmitted field can occupy the main energy. And as modes are excited one by one, the proportion of energy of higher modes of the reflected field and the transmitted field shows a “trade-off” state in the full frequency range. The energy distribution law will not be significantly changed when the elastic layer materials on both sides are exchanged, or the elastic layers thickness and the stiffness ratio is changed. On the whole, the energy is more easily concentrated in the softer elastic layer, and guided wave mode is more active in the initial frequency band after excitation and distributes more energy.