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Importance of Fracturing Hard and Massive Overlying Strata for Complete Extraction of Thick Coal Seam — Case Studies

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Journal of the Geological Society of India

Abstract

Engineering efforts need to be organized as per the rock mechanic conditions of the site for efficient underground extraction of a thick coal seam. Geo-mining conditions of Indian coalfields have favoured development of thick coal seams on Bord and Pillar (B&P) method, where single lift depillaring of total thickness (SLDTT) is vital for their final extraction. Competency of heightened pillar is an important factor for uncontrolled roof-pillar interaction during caving of the hard and massive overlying strata. An increase in extraction height by underwinning of roof coal band of the thick coal seam during retreat, developed along its floor horizon, is found to be the main reason for the strength deterioration. Conducted field studies also showed that the presence of competent overlying strata caused caving after a large overhang inside the goaf varying from 6000 m2 to 12500 m2. An attempt was made to control the roof caving by a proportional increase in width of the heightened pillars and it worked well but caused the issue of resource conservation. However, another field study with SLDTT working below laminated and weak overlying strata experienced a smooth strata control condition. This fortifies the idea of strength reduction of the competent overlying strata by fracturing for a controlled strata behaviour. This paper presents the result of the field investigations to demonstrate the role of strength reduction of overlying strata for underground extraction of total thickness of a thick coal seam in single lift.

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Acknowledgements

Authors are highly obliged to Director, CSIR-CIMFR, for his permission to publish this paper. Authors are also obliged to the colliery management of each mine for their valuable co-operation during the field observation. The views expressed in this paper are those of the authors and not necessarily of the institute to which they belong.

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Authors and Affiliations

  1. CSIR-CIMFR (CSIR-Central Institute of Mining and Fuel Research), Barwa Road, Dhanbad, 826 015, India

    Rakesh Kumar, Ashok Kumar, Arun Kr. Singh & Amit Kr. Singh

  2. Indian Institute of Technology (Indian School of Mines), Dhanbad, 826 015, India

    Arvind Kr. Mishra

  3. National Institute of Technology, Rourkela, 769 008, India

    Sahendra Ram

  4. School of Mines and Metallurgy, Kazi Nazrul University, Asansol, 713 340, India

    Rajendra Singh

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  1. Rakesh Kumar
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  2. Arvind Kr. Mishra
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  3. Ashok Kumar
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  4. Arun Kr. Singh
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  5. Sahendra Ram
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  6. Amit Kr. Singh
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  7. Rajendra Singh
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Correspondence to Rakesh Kumar.

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Kumar, R., Mishra, A.K., Kumar, A. et al. Importance of Fracturing Hard and Massive Overlying Strata for Complete Extraction of Thick Coal Seam — Case Studies. J Geol Soc India 98, 203–210 (2022). https://doi.org/10.1007/s12594-022-1960-y

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  • DOI: https://doi.org/10.1007/s12594-022-1960-y

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