Microhardness of Coal from Near-Fault Zones in Coal Seams Threatened with Gas-Geodynamic Phenomena, Upper Silesian Coal Basin, Poland
Abstract
:1. Introduction
2. Description of the Research Problem
3. Research Methodology
- Fmax—maximal force (N),
- hc—depth of impact (µm),
- Ac—developed contact area (µm2).
- EIT—elastic modulus [GPa]
- Ei—elastic modulus of indenter (1141 GPa)
- vi—Posson’ ratio of the indenter (0.07)
- Er—reduced modulus of the indentation contact
- vs—Posson’ ratio of the sample (user’s selection).
4. Research Material
- Unaltered coal—The sole subject of the analysis was the most common maceral from the vitrinite group, i.e., colotelinite. The surface of the analyzed areas was free from exogenic fractures. The only fractures that could be observed in this coal were single and regular endo-microfractures, i.e., fractures resulting from natural coalification processes.
- Altered coal:
- a.
- Cracked coal—It was assumed that the diagnostic feature of this type of structure should be the presence of a network of irregular cracks that appeared as a result of the impact of the exogenic forces, observed in colotelinite.
- b.
- Cataclastic coal—In the areas classified as cataclastic coal, we can identify a dense or a very dense network of cracks. Some coal fragments are comminuted to a large extent and mixed. The original structures are partly or totally blurred.
- c.
- Mylonitic coal—These structures are characterized by a very high degree of transformation. Particular fragments, previously ground, are dislocated in relation to one another and show traces of secondary pressing. The original structures are totally blurred. Thus, directional structures and secondary cracks may appear.
- The W1 sample was taken from the “Borynia–Zofiówka–Jastrzębie” hard coal mine, coal seam no. 404/1 + 405/1. The material comes from the mine face of the ventilation plane V, located at the depth of 1000 m. In August 2010, a sudden outburst of methane occurred in the area, combined with the dislocation of rock material into the mine face. A sample from a sidewall in the vicinity of the fault was selected for microhardness tests. The total content of ‘structurally altered’ coal in the sample was over 17 percent (Table 1);
- The W2 sample was taken from the “Borynia–Zofiówka–Jastrzębie” hard coal mine, seam no. 409/4. In November 2005, an outburst of methane and rocks occurred in the D-6 gate road. After the incident, two faults were revealed, situated in the post-outburst cavern area [12,14]. For the microhardness tests, a sample from the right sidewall of the fault was selected, containing almost 50 percent of structurally altered coal (Table 1);
- The W3 sample was taken from the “Pniówek” hard coal mine, coal seam no. 403/3. In the B-5 longwall, a minor tectonic discontinuity cutting through the seam was discovered, with the upthrown side on the left. For the microhardness tests, a sample from the right side of the fault was selected, containing ca. 50 percent of structurally altered material (Table 1);
- The W4 sample was taken from the “Borynia–Zofiówka–Jastrzębie” hard coal mine, coal seam no. 412 łg + łd. In the G-2 top gate, a fault with a minor left thrust was discovered. For the microhardness tests, a coal hunk extracted from the spot located 1.5 m away from the fault was selected. The content of structurally altered coal in this sample is about 20 percent (Table 1);
- The W5 sample was taken from the “Borynia–Zofiówka–Jastrzębie” hard coal mine, seam no. 406/1. In the F-1 top gate, a fault was revealed, from which samples were extracted for the purpose of further analysis. The content of structurally altered coal material in this sample is circa 44 percent (Table 1);
- The W6 sample was taken from the “Borynia–Zofiówka–Jastrzębie” hard coal mine, seam no. 407/1. The research sample was extracted from the spot located over 10 m away from the fault. This sample contains just a small amount of structurally altered coal material (less than 2 percent of the total capacity–Table 1).
5. Obtained Results
5.1. Vickers Microhardness Analyses
5.2. Elasticity Modulus
5.3. Characteristic Impressions
6. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Sample No. | W1 | W2 | W3 | W4 | W5 | W6 | |
---|---|---|---|---|---|---|---|
Distance from the fault/grain fraction of the sample | Sidewall—fault area (1–2 mm) | Fault—right sidewall (0.5–1 mm) | Fault—right wing (0.5–1 mm) | 1.5 m to the right from the fault (0.5–1 mm) | The fault (0.5–1 mm) | Distance from the fault >10 m (0.5–1 mm) | |
Unaltered coal | 82.66 | 52.01 | 49.80 | 80.69 | 56.34 | 98.32 | |
Structurally altered coal | Cracked coal | 10.6 | 9.50 | 17.40 | 7.36 | 10.23 | 1.32 |
Cataclastic coal | 1.23 | 30.92 | 21.77 | 8.67 | 30.80 | 0.36 | |
Mylonitic coal | 5.25 | 7.57 | 11.03 | 3.28 | 2.63 | 0.00 |
Sample No. | Mean Vitrinite Reflectance Value R0 (%) |
---|---|
W1 | 1.09 |
W2 | 1.11 |
W3 | 0.98 |
W4 | 0.98 |
W5 | 1.04 |
W6 | 1.11 |
Statistical Parameters | Vickers Microhardness HV (N/mm2) | Modulus of Elasticity EIT (GPa) | |
---|---|---|---|
Unaltered vitrinite | Mean | 58.66 | 5.87 |
Maximum | 69.79 | 6.91 | |
Minimum | 43.81 | 4.97 | |
Number of measurements | 30 | 30 | |
Standard deviation | 6.63 | 0.48 | |
Cracked vitrinite | Mean | 50.41 | 5.51 |
Maximum | 65.05 | 7.03 | |
Minimum | 39.43 | 4.52 | |
Number of measurements | 19 | 19 | |
Standard deviation | 8.69 | 0.74 | |
Cataclastic coal | Mean | 44.78 | 5.16 |
Maximum | 53.78 | 6.44 | |
Minimum | 33.40 | 4.08 | |
Number of measurements | 36 | 36 | |
Standard deviation | 5.71 | 0.50 | |
Mylonitic coal | Mean | 57.53 | 5.80 |
Maximum | 67.94 | 8.36 | |
Minimum | 44.71 | 4.54 | |
Number of measurements | 24 | 24 | |
Standard deviation | 5.40 | 0.82 |
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Godyń, K.; Kožušníková, A. Microhardness of Coal from Near-Fault Zones in Coal Seams Threatened with Gas-Geodynamic Phenomena, Upper Silesian Coal Basin, Poland. Energies 2019, 12, 1756. https://doi.org/10.3390/en12091756
Godyń K, Kožušníková A. Microhardness of Coal from Near-Fault Zones in Coal Seams Threatened with Gas-Geodynamic Phenomena, Upper Silesian Coal Basin, Poland. Energies. 2019; 12(9):1756. https://doi.org/10.3390/en12091756
Chicago/Turabian StyleGodyń, Katarzyna, and Alena Kožušníková. 2019. "Microhardness of Coal from Near-Fault Zones in Coal Seams Threatened with Gas-Geodynamic Phenomena, Upper Silesian Coal Basin, Poland" Energies 12, no. 9: 1756. https://doi.org/10.3390/en12091756