Effects of torpedo blasting on rockburst prevention during deep coal seam mining in the Upper Silesian Coal Basin

In the Upper Silesian Coal Basin(USCB),coal seams are exploited under progressively more difficult geological and mining conditions(greater depth,higher horizontal stress,more frequent occurrence of competent rock layers,etc.).Mining depth,dislocations and mining remnants in coal seams are the most important factors responsible for the occurrence of rockburst hazards.Longwall mining next to the mining edges of neighbouring coal seams is particularly disadvantageous.The levels of rockburst hazards are minimised via the use of rockburst prevention methods.One active prevention method is torpedo blasting in roof rocks.Torpedo blastings are performed in order to decrease local stress concentrations in rock masses and to fracture the roof rocks to prevent or minimise the impact of high-energy tremors on excavations.The estimation of the effectiveness of torpedo blasting is particularly important when mining is under difficult geological and mining conditions.Torpedo blasting is the main form of active rockburst prevention in the assigned colliery in the Polish part of the USCB.The effectiveness of blasting can be estimated using the seismic effect method,in which the seismic monitoring data and the mass of explosives are taken into consideration.The seismic effect method was developed in the Czech Republic and is always being used in collieries in the Czech part of the coal basin.Now,this method has been widely adopted for our selected colliery in the Polish part of the coal basin.The effectiveness of torpedo blastings in the faces and galleries of the assigned longwall in coal seam 506 has been estimated.The results show that the effectiveness of torpedo blastings for this longwall was significant in light of the seismic effect method,which corresponds to the in situ observations.The seismic effect method is regularly applied to estimating the blasting effectiveness in the selected colliery.

The influence of mining factors on seismic activity during longwall mining of a coal seam

In this article an attempt to determine the influence of mining factors on the seismic activity during the longwall mining of the upper layer of coal seam no.405/2 in one of the Polish hard coal mines in the Upper Silesian Coal Basin was conducted.Two longwall panels were mined in analogous geological conditions and based on the same mining system and technology.However,there was significant difference with regards to the mining factors,which was reflected in the observed seismic activity.Some tools used in mining seismology were applied to illustrate the aforementioned influence of mining factors,e.g.the frequency-energy distribution,the frequency-magnitude distribution,the 2 D distribution of released seismic energy,the relationship between released seismic energy and the volume of mined coal,the Benioff strain release,and the Gutenberg-Richter(GR)b coefficient distribution(b is the proportion between high and low energy tremors).Concerning the Benioff strain release,a new solution,based on the slope of a fitted line in a moving time window,is proposed.

Comprehensive use of the Gutenberg–Richter law and geotomography for improving seismic hazard evaluation in hard coal mines

Mining-induced seismicity occurs in numerous underground mines worldwide where extraction is conducted at great depths or in areas characterised by complex tectonic structure.It is accompanied by rock bursts,which result in the loss of working functionality and the possibility of accidents among personnel.The issue of a constant and reliable seismic hazard evaluation is of key signifcance for both the safety of miners and the stability of production.Research on its improvement is directed at developing new interpretive solutions and methods.The nature of the presented solution is the complex interpretation of seismological data that characterise rock mass seismicity and of underground measurement results in the form of a map presenting the longitudinal wave propagation velocity distribution in the rock surrounding the mined coal seam.The solution was tested in hard coal mines located in the Upper Silesian Coal Basin.The mines are equipped with a modern seismological system enabling the constant monitoring of seismicity together with hazard level evaluation as well as with seismic apparatus for conducting periodic measurements of the seismic wave propagation velocity before the mining face.Comprehensive seismic hazard evaluation criteria were determined based on the obtained results,involving the anomaly of the Gutenberg–Richter law“b”value and the maximum longitudinal seismic wave propagation velocity in the roof rock.The obtained experience and the result validation of this new comprehensive hazard evaluation method confrm its practical usefulness and indicate the directions of improvement for the solution in question.

Correction to:Application of long-reach directional drilling boreholes for gas drainage of adjacent seams in coal mines with severe geological conditions

Correction:International Journal of Coal Science&Technology(2022)9:88 https:/doi.org/10.1007/s40789-022-00553-6 In this article,the author would like to change the Ethics Declaration as below:EthicsDeclarations Scientific work published within the framework of an international project DD-MET co-financed by the Research Fund for Coal and Steel(RFCS),(Grant Agreement:847338)and by the Polish Ministry of Science and Higher Education(Contract no.5073/FBWiS/19/2020/2 and 5038/FBWiS/2019/2).

Use of coals and wastes in a co-gasification process aimed at producing hydrogen rich gas

The use of low-quality coals and flotoconcentrates is currently severely limited,and the problem of managing municipal waste from anthropogenic activities is currently a challenge.The problems of reducing carbon dioxide emissions,utilizing the energy potential of waste and increasing its recycling have an impact on the costs of electricity production.Considering the abundant streams of unused fuels,they can be considered as attractive energy materials,so environmentally-friendly and cost-effective options for their utilization should be developed.A study was conducted using steam co-gasification technology on selected coals,flotation concentrates and Refuse Derived Fuel(RDF)alternative fuel.Selected low-quality coals were combined with RDF alternative fuel in a process aimed at hydrogen production.The experiments produced gas with hydrogen concentrations ranging from 67%(vol.)to 68%(vol.)with low methane concentrations.It was observed that the addition of alternative fuels helped to increase the hydrogen concentration in syngas.Attention was paid to the catalytic ability of the metal oxides contained in the fuel blend,with particular reference to K_(2)O and Al_(2)O_(3)and TiO_(2).

Spatiotemporal analysis of elastic and inelastic deformations in roof-rocks from seismological observations

The spatiotemporal analysis of seismic zones characterised by the scattering and accumulation of strain energy in the roof-rocks of the excavated longwall panel where inelastic or elastic deformations occurred during hard coal seam mining is discussed.The studied longwall panel was designed to utilize the effect of partial stress relaxation caused by the earlier extraction of the coal seams located above.A full seismic moment tensor and spectral source parameter analyses were used to obtain information about the degree of inelastic and elastic coseismic deformations.This study also showed that these deformation changes correspond to variation in the Benioff strain release characteristics.Next,analyses of deformation zones were compared with the relationship between radiated energy and the excavated volume of rocks per month.The concept of balanced seismic energy release assumed the exponential increase of released seismic energy with the increase in the volume of excavated rock.Discrepancies between the observed and predicted radiated energies indicated that strain energy in selected zones in the rock mass was either scattered if the prediction was overestimated,or accumulated if underestimated.Moreover,the study showed that elastic deformation in one zone can lead to inelastic deformation in the same zone.

Application of long-reach directional drilling boreholes for gas drainage of adjacent seams in coal mines with severe geological conditions

This study aimed to demonstrate the application of Long Reach Directionally Drilled Boreholes(LRDD)for gas drainage of adjacent seams before and during the longwall face operations of low permeability-high gas content coals Staszic-Wujek Hard Coal Mine in the Upper Silesia Coal Basin(Poland).Five LRDD Boreholes(TM1a-TM5)with a length of 300 and 400 m were located over coal seam 501 in the fractured zone and monitored over six months of longwall face operations.LRDD Boreholes were combined with Cross-Measured Boreholes.Reservoir characterization and geological modeling supported the results obtained from gas drainage.The drainage efficiency of LRDD Boreholes was the approxi-mately 70%level,while conventional Cross-Measured Boreholes were only 30%.The highest goaf gas quality(94%methane concentration)was reported for TM4,placed at an average elevation of 41 m above coal seam 501.The highest goaf gas production(average 6.2 m^(3)/min)was reported for LRDD Borehole TM3.This borehole was placed within the fracture zone(average elevation of 24.4 m)and drilled through the sandstone lithotype with the best reservoir properties,enhancing drainage performance.LRDD Boreholes TM2 and TM4 achieved similar performance.These three LRDD Boreholes were drilled close to the maximum principal horizontal stress direction,providing borehole stability during under-mining.The lowest goaf gas production was reported for LRDD Boreholes TM1a and TM5.Both Boreholes were placed in the rubble zone.