Assessment of the impact of an overlying coal seam edge using seismic profiling of refracted Pwave velocity

Abstract

This paper presents the results of seismic profiling along the sidewalls of two headings of a longwall in a coal-seam at a depth of about 850 and 870 metres in a coal mine in the Upper Silesian Coal Basin, Poland. The seismic profiles were located in a zone of impact of the same overlying edge of the coal-seam located about 40 m above. This study was interesting from that point of view since there were no other geological and mining factors present which could disturb the impact of the coal seam edge. The profiling of refracted P-wave velocity changes was carried out according to the Dubinski method. This method is used for the assessment of relative stress in a coal seam in the side wall of the excavation. The results obtained on both seismic profiles are very similar, which demonstrates the small impact of the overlying edge of the coal seam in both headings of a longwall. It should be emphasised that at greater exploitation depths, the calculated reference velocity is less reliable than the measured reference velocity. Presumably, the method of calculating seismic anomaly requires updating under such conditions, but additional evidence should be collected.

Comparison of the results of the seismic profiling and WAS-96/RMS seismoacoustic active method in an assessment of the impact of the overlying coal seam edge

“…1) or measured velocity in the region outside of anomaly. The error of the measured velocity did not exceed 50m/s [18].…”

“…One of the basic ones is stress concentration in coal seams which occurs in particular as a result of the impact of the edges and remnants of adjacent coal seams [7][8][9]. The magnitude of such impacts is commonly recognized by seismic profiling [1,[10][11][12][13][14][15][16][17][18]. Refracted P-wave velocity profiling used to be performed according to the Dubiński method [10] updated in the work of Dubiński and Konopko [1].…”

Reference P-wave velocity in coal seams at great depths in Jastrzebie coal mine

“…An additional problem is related to the fact that the velocity of the determined Pwave does not differ significantly from the velocity of the refracted S-wave in shale layers in the roof and the bottom of the coal seam (Fig. 2) [14]. At greater distances from the excitation point, the first breaks of the refracted P-wave in shale layers overtakes or distorts the first breaks of the P-wave in the coal seam.…”

“…Szreder and Barnas [14] reported that "seismic profiling in underground excavations was also carried out for different purposes in other geological conditions for example: in a salt body to estimate the width of the fracture zone in the side-walls of excavations [15] and also in tunneling [16][17]"…”