• Dynamic analysis of fault slips and their influence on coal mine rib stability

    Historical data indicate that in deep coal mines the presence of faults in close
    proximity to excavations affect the frequency of coal bursts. A number of researchers have
    attempted to correlate the fault geometries to the frequency and severity of coal bursts but
    dynamic numerical modelling has not been used to show how faults can affect coal ejection
    from the rib side. The dynamic numerical analysis presented here show how different
    orientations of fault slips may affect coal bursts. To prove the concept, 89 cases of slipping fault
    geometries were modelled using the FLAC3D software and their effect on rib stability
    investigated. The results indicate that there is a simple and logical correlation between the fault
    location, its slip velocity and the ejection of the yielded coal rib side. The seismic compressive
    wave generates rock/coal mass velocities that directly impact the rib side. If the coal rib is
    relatively disturbed and loose, these velocities can cause its ejection into the excavation. The
    slip direction typically impacts one side of the mine roadway only. A 1 m thick loose coal block
    attached to the 3 m high rib side in mine roadway was ejected at speeds ranging from 2.5 to 5
    m/s depending on the fault location, its orientation and the maximum fault slip velocity modelled
    at 4 m/s. Dynamic-analysis-of-fault-slips-and-their-influence-on-coal-mine-2020-GV.pdf1.6 MB
  • Dynamic events at longwall face, CSM Mine, Czech Republic

    Presented here are the details of the seismic events that occurred at longwall 11
    located at the CSM mine in the Ostrava coal region, Czech Republic. This longwall was
    excavated in a very complex area located within the shaft protective pillar and adjacent to the
    50 m wide and steeply inclined fault zone at a depth of 850 m. In addition, 10 longwalls were
    extracted below each other over many years in several sloping seams located on the other side
    of the large sloping fault zone resulting in complex stress fields and large subsidence. The
    immediate roof above longwall 11 was a very strong sandstone and sandy siltstone with a
    uniaxial compression strength of 80 – 160 MPa. When the longwall started, continuous seismic
    monitoring of the longwall area indicated 470 small seismic events with energy smaller than
    <102 J. The first high energy event of 3.3*105 J occurred when the longwall advanced 85m past
    the starting line. Some 30 minutes later a rockburst occurred registering energy of 2.2 *106 J,
    causing significant rockburst damage at the tailgate located near the large tectonic zone. The
    roadway steel arches were significantly deformed and the maximum floor heave reached up to
    1.5 m. To investigate the complex strata behavior in that area, a large FLAC3D model 0.27 km3
    in volume was constructed and 10 longwalls were extracted in several sloping seams adjacent
    to the large fault zone. The model under construction is now ready to study the complex strata
    behaviour and the associated stress fields together with the dynamic strata behaviour to match
    the modelled seismic events with those measured underground. Dynamic-events-at-longwall-face-2020-GV.pdf1.8 MB
  • Numerical model of dynamic rock fracture process during coal burst

    Coal bursts present one of the most severe hazards challenging the safe
    operations in underground coal work environments. In Australia, these events are becoming
    increasingly frequent as coal measures are mined progressively deeper. This study is
    supported by the Australian Coal Association Research Program (ACARP) which aims to better
    understand the phenomena of coal burst. In this paper the dynamic fracture process of coal
    bursts was successfully simulated in the coal roadway. This was achieved using dynamic
    analysis utilising DRFM2D routine by Venticinque and Nemcik (2017) in FLAC2D (Itasca, 2015)
    which complemented previous study observations by Venticinque and Nemcik (2018). This is
    significant because until now the evolving dynamic rock fracture process during coal burst
    remained unknown. Additionally, coal/rock burst events were shown from simulation as being
    largely driven by the propagation of shear fractures from within the rib. This was demonstrated
    to produce effect forcing the dynamic conversion and release of potential energy stored as
    compressive strain in the rib into kinetic movement of the entire rib section. This entire process
    was shown to occur very fast taking approximately 0.2 seconds for a coal burst to fully establish,
    with ejection of several meters of rib at a velocity of 1.6 m/s produced in the model of an
    underground coal roadway having 550 m depth of cover.
    Numerical-model-of-dynamic-rock-fracture-process-during-coal-burst-2020-GV.pdf960 KB
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