Abstract:

The article describes the results of uniaxial compression tests of rectangular specimens made of geomaterial with a view to investigate coal-rock contact conditions on a lab scale. Based on the acoustic sounding data, tomography was carried out to find spatial distribution of longitudinal wave velocity V in a specimen per stages of loading. Using the empirical relation V(σ), the mean normal stress s was calculated and taken as the input data in the solution of an inverse problem for determination of boundary conditions. The model calculations show that under vertical compression, near slip sections of coal-country rock contact, areas of horizontal tension arise, which are the most probable sources of failure and outbursts.

1 Introduction

Coal cutting process is accompanied by rapid alternation of stresses in rock mass, which occasionally induces dynamic phenomena such as gas outbursts and rock bursts (Seidle 2011, Bondarenko et al. 2014, Mark & Gauna 2016, Mark 2018). With a view to controlling coal-rock mass conditions and predicting such dynamic phenomena, mines are equipped with microseismicity monitoring systems (Luxbacher et al. 2008, Zhenbi & Baiting 2012, Al Heib 2012, NIOSH 2016). At the same time, modern methods of mine seismicity data interpretation fail to detect discontinuities having linear sizes of a few centimeters (Palmer 1987, Henson & Sexton 1991, Cocker et al. 1997, Khukhuudei & Khukhuudei 2014). Such discontinuities include thin contact zones between coal and enclosing rocks, and their acoustic properties differ slightly (Mironov 1988). In the meanwhile, the presence of areas with the decreased friction factor in coal-rock contact zones can be a cause of cleavage fracture of coal face and subsequent coal and gas outbursts (Karchevsky et al. 2017). The specified areas introduce qualitative changes in stress state of coal-rock mass, which can be detected using acoustic methods of mine geophysics (Everett 2013, Telford et al. 1990).

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