Dynamic model of fault slip and its effect on coal bursts in deep minesPublished Feb, 2021The success of deep mining operations relies upon controlling the fractured ground. It is a documented knowledge that many coal bursts occur when mining close to the existing faults. Gradual stress relief towards excavations and other mechanisms can unload stress normal to the nearby fault plane causing it to slip. The generated seismic waves impact the mine roadway rib sides and can produce a coal burst. As part of the ACARP project, the FLAC3d dynamic numerical model was used to show how a fault slip at various locations and orientations may initiate a coal burst. This study simulates an artificial fault slip with peak velocity reaching 4m/s in 0.013 seconds and displacing 119mm in total. Seismic induced peak particle velocities in rock and its influence on coal rib stability were investigated. 89 numerical models with various fault locations and orientations at 450m depth indicated that a 4 tonne coal block can be ejected from the mine roadway rib side at speeds of up to 5m/s. The important finding is that irrespective of the fault slip magnitude, the fault geometry and the in-situ stresses enable to predict which side of the mine roadway may experience the coal burst. Instructing the mine personnel to use the other side of the roadway may improve their safety. Overall, this research produced preliminary results to prove that this method can be used to flag the coal burst dangers for certain fault locations and orientations in deeper mines irrespective of the fault slip properties that are typically difficult to predict. Dynamic-model-of-fault-slip-and-its-effect-on-coal-bursts-in-deep-GV.pdf933 KB
Dynamic analysis of fault slips and their influence on coal mine rib stabilityPublished Feb, 2020Historical 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 RepublicPublished Feb, 2020Presented 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 burstPublished Feb, 2020Coal 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.