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Powered Support in Dynamic Load Conditions – Numerical Analysis

Wojciech Masny
Archives of Mining Sciences | 2020 | vol. 65 | No 3 | 453-468 | DOI: 10.24425/ams.2020.134129
Keywords hard coal rock burst dynamic powered support numerical modelling
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Abstract

Tremors occur randomly in terms of time, energy as well as the location of their focus. The present state of knowledge and technology does not allow for the precise prediction of these values. Therefore, it is extremely important to correctly select a powered roof support for specific geological and mining conditions, especially in the case of areas where dynamic phenomena are often registered. This article presents information on rock burst hazard associated with the occurrence of rock mass tremors and their influence on a powered roof support. Furthermore, protection methods of a powered roof support against the negative effects of dynamic phenomena are discussed. As a result of an analysis the methodology, to determine the impact of dynamic phenomena on the powered roof support in given geological and mining conditions is presented.

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Authors and Affiliations

Wojciech Masny
ORCID: ORCID

Field Testing of the Methods for Prevention and Control of Coal and Gas Outburst – A Case Study in Poland

Phu Minh Vuong Nguyen Piotr Litwa Marek Przybylski
Archives of Mining Sciences | 2023 | vol. 68 | No 4 | 639-654 | DOI: 10.24425/ams.2023.148154
Keywords Gasogeodynamic phenomena coal and gas outbursts rock bursts coal mining
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Abstract

Coal mining tends to face increasing stress and gas conditions when it extends to deeper levels. The mining-induced high stress and gas pressure concentrations often result in gasogeodynamic phenomena such as rock bursts and coal & gas outbursts. Over the last decades, these gasogeodynamic events have been observed more often in the Upper Silesian Coal Basin, Poland. With the increasing mining depth, these hazards not only become a serious safety risk but also represent a significant challenge for coal mining. In order to eliminate future hazards and improve safety in underground coal mines, it is necessary to apply particular methods for the prevention and mitigation of possible hazards during mining operations. Inaction or incorrect use of preventive measures may lead to gasogeodynamic events, which may result in accidents and material losses, thereby affecting the mine’s economic performance. Several coal mines operated by Jastrzębska Spółka Węglowa S.A. (JSW group), such as Pniówek, Budryk and Zofiówka coal mines have been identified as the area most prone to rock bursts as well as coal and gas outburst. Generally, the longwall panels often experience a high degree of these mining hazards. Therefore, the main aim of this research is to examine and optimise the possibility of application of prevention methods in order to reduce the frequency and scale of dangerous gasogeodynamic phenomena such as coal and gas outburst. As a main part, the field testing of the selected preventive methods that were conducted in the JSW coal mines. Based on the obtained results, the possibility of application of an optimal method for the prevention and control of coal and gas outburst in the geo-mining conditions of the JSW coal mines was discussed. The research results could be an example for other coal mines in mine planning and designing in the gasogeodynamic (coal and gas outburst) hazard-prone conditions.
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Authors and Affiliations

Phu Minh Vuong Nguyen
1
ORCID: ORCID
Piotr Litwa
1
ORCID: ORCID
Marek Przybylski
2
ORCID: ORCID
  1. Central Mining Institute, Department of Extraction Technologies, Rockburst and Risk Assessment, 1 Gwarków Sq., 40-166 Katowice, Poland
  2. Jastrzębska Spółka Węglowa S.A., Pniówek Coal Mine, 18 Krucza st. 43-250, Pawłowice, Poland

Experimental Study on Deformation and Damage Evolution of a Mining Roadway with Weak Layer Rock under Compression-shear Load

Yimin Song He Ren Hailiang Xu Dong An
Archives of Mining Sciences | 2021 | vol. 66 | No 3 | 351-368 | DOI: 10.24425/ams.2021.138593
Keywords rock burst zonal fracturing compression-shear load interlayer displacement Digital Speckle Correlation method
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Abstract

The structure and load characteristics of the roadway are simplified, and the experimental model of the roadway deformation and damage under compression-shear load is established. The experimental data acquisition system is built with a CCD camera. The digital speckle correlation method is used to calculate the image data of the experimental model. The correspondence between the evolution law of the deformation field, the interlayer displacement and deformation evolution are analysed, including the dynamic characteristic of the roadway surrounding the rock. Research results indicate: (1) The damage peak load of the weak layer structure shows a decreasing trend as the interlayer shear stress increases. As the initially applied shear stress increases, the value of interlayer sliding displacement increases, and the dynamic characteristics become more apparent. (2) In the sub-instability phase of the loading curve, when the surrounding rock slides along the layers under compression-shear load, the stress is re-distributed and transmitted to the deep part of the surrounding rock. Then the surrounding rock of the roadway forms the characteristic of alternating change, between tension to compression. (3) According to the state of dynamic and static mechanics, the deformation evolution of the roadway before the peak load belongs to the static process. Zonal fracturing is part of the transition phase from the static process to the slow dynamic process, and the rockburst damage is a high-speed dynamic process. (4) Under the compression-shear load, due to the weak layer structure of the coal and rock mass, the local fracture, damage, instability and sliding of the surrounding rock of the roadway are the mechanical causes of rockburst. (5) Even if the coal and rock mass does not have the condition of impact tendency, under stress load of the horizontal direction, distribution of large shear stress is formed between layers, and the dynamic damage of the rockburst may occur.
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Bibliography

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Authors and Affiliations

Yimin Song
1
He Ren
1
Hailiang Xu
1
Dong An
1
  1. North China University of Technology, School of Civil Engineering, China

Experimental and Theoretical Study on the Dynamic Ejection Process of a Rock Burst Under a Static Load

Weiyu Zheng
Archives of Mining Sciences | 2021 | vol. 66 | No 1 | 43-56 | DOI: 10.24425/ams.2021.136691
Keywords rock burst high-speed camera kinetic energy stress field crack propagation
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Abstract

As the duration of a rock burst is very short and the roadway is seriously damaged after the disaster, it is difficult to observe its characteristics. In order to obtain the dynamic characteristics of a rock burst, a modified uniaxial compression experiment, combined with a high-speed camera system is carried out and the process of a rock burst caused by a static load is simulated. Some significant results are obtained: 1) The velocity of ejected particles is between 2 m/s and 4 m/s. 2) The ratio of elastic energy to plastic energy is about five. 3) The duration from integrity to failure is between 20 ms and 40 ms. Furthermore, by analyzing the stress field in the sample with a numerical method and crack propagation model, the following conclusions can be made: 1) The kinetic energy of the ejected particles comes from the elastic energy released by itself. 2) The ratio of kinetic energy to elastic energy is between 6% and 15%. This can help understand the source and transfer of energy in a rock burst quantitatively.
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Authors and Affiliations

Weiyu Zheng
1 2
  1. China University of Mining & Technology (Beijing), School of Energy and Mining Engineering, China
  2. State Key Laboratory of Coal Mining and Clean Utilization, China

Comparative Testing of Cable Bolt and Wire Rope Lacing Resistance to Static and Dynamic Loads

Andrzej Pytlik Mariusz Szot
Archives of Mining Sciences | 2023 | vol. 68 | No 4 | 707-724 | DOI: 10.24425/ams.2023.148158
Keywords Rock support cable bolts wire rope lacing rock bursts drop weight impact method
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Abstract

The conduction of mining activity under the conditions of rock bursts and rock mass tremors means that designers often utilise support systems comprising various configurations of steel arch, rock bolt and surface support. Particularly difficult geological and mining conditions, when wire mesh does not provide sufficient dynamic resistance, it requires an additional reinforcement with wire rope lacing in the form of steel ropes installed between the bolt ends and fixed to them by means of various rope clamps (e.g. u-bolt clamps). Bench tests were conducted to compare the strength of wire ropes under static and dynamic loading. The tests involved wire ropes with an internal diameter of Ø15.7 mm. Tests under static loading demonstrated that the cable bolts transferred a maximum force Fs max = 289.0 kN without failure, while the energy absorbed until failure was E 1s = 16.6 kJ. A comparative test result analysis for the wire ropes used in the bolt designs revealed that the influence of dynamic loading forces has a significant effect on reducing the rope load capacity, which results in the brittle cracking of the wires in the rope. Although the average dynamic force leading to wire rope failure F dmax = 279.1 kN is comparable to the minimum static force Fmin = 279 kN defined in the relevant standard, the average energy E1d absorbed by the cable bolt until failure is 48% lower than the energy E1s determined for wire rope failure under static loading. Furthermore, cable bolt failure under dynamic loading occurred at an impact velocity of the combined ram and crosshead masses ranging within vp = 1.4-1.5 m/s.
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Authors and Affiliations

Andrzej Pytlik
1
Mariusz Szot
1
ORCID: ORCID
  1. GIG – National Research Institute, Plac Gwarków 1, 40-166 Katowice, Poland

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