Estimating S-wave velocity of a coal seam excavation damaged zone in the vicinity of an underground coal mine roadway

Abstract

We present a new approach for estimating the S-wave velocity of the fractured coal seam in the vicinity of the underground roadway. We use so-called roadway mode – the dispersive wave which propagates close to the roadway sidewall. To better understand the complex seismic wavefield generated around the underground coal mine roadway, we use 3D finite-difference simulations. Modelling confirmed that the roadway mode in the horizontal plane in the center of the seam and for higher frequencies strives to the fundamental mode of the Rayleigh tunnel surface wave in the coal layer. Therefore, the S-wave velocity model can be obtained from its group or phase velocity dispersion curve. The applicability of this method is demonstrated with the data from a 2-m thick coal seam from the Rydułtowy mine, Poland. Derived quasi 2D S-wave velocity profile strongly correlates with the mechanical quality of the sidewall. We notice a velocity decrease for the damaged part of the roadway. The method can be routinely applied to image and monitor fractured coal seam near a roadway in the underground coal mine to improve safety and reduce economic loss while mining. Note: This paper was accepted into the Technical Program but was not presented at IMAGE 2021 in Denver, Colorado.