Insights into coupling mechanisms of multimode surface waves

摘要

Based on three synthetic models, coupling mechanisms of multimode surface waves are theoretically analyzed to provide powerful insights into contributions of multiple modes to surface wave dispersion characteristics. Modeling results demonstrate that: (1) For a normally dispersive profile (a model with stiffness increasing with depth), the fundamental mode is strongly predominant on higher modes at every frequency, and hence the superposed dispersion curve is practically coincident with the fundamental mode one; (2) For an inversely dispersive profile (such as, a model with a soft layer trapped between two stiff layers or a model with a stiff layer sandwiched between two soft layers), the fundamental mode is not dominant in the high frequency range or in the middle frequency range, and more modes participate to the definition of Rayleigh wave dispersion with increasing frequency. In this case the superposed dispersion curve is not monotonically decreasing with increasing frequency but is a combination of the individual mode phase velocities in the corresponding frequency range, which accounts for the mechanism of zigzag dispersion curves, i.e., zigzag dispersion curves arise from mode superposition of multiple modes of surface waves. We verify our modeling results with a real-world example from a pavement system in Henan, China.