Influence of Physical Parameters of Coal Seam on “Cross” Phenomenon of Rayleigh In-seam Wave Dispersion Curve

Abstract

Dispersion curves of Rayleigh channel waves may have “cross” between the fundamental and first higher order modes either in the phase velocities or in group velocities in the low frequency band. It was observed that such phenomenon can lead to wrong interpretation of dispersion curves. In order to study the cross of dispersion curves, considering the changes of these parameters, such as the velocity and density of the coal seam and country rocks, and the thickness of the coal seam, we present multi-group of dispersion curves of Rayleigh channel waves computed by the generalized reflection-transmission coefficient method, based on a three-layer symmetrical model of rock-coal-rock. What’s more, the staggered-grid higher order finite difference method is used to simulate the channel waves for verification of extracted dispersion curves. Results show that the cross of dispersion curves of the Rayleigh channel waves depend greatly on the S-wave velocity difference between the coal and rocks, more difference, more “cross”, but the influence of thickness, density and P-wave velocity of the coal seam are not significant compared with S-wave velocity.

Keywords

• rayleigh channel waves
• dispersion curve
• generalized reflection-transmission coefficient
• “cross”
• numerical simulation