Abstract
This research focuses on the strata control issues in a Bord and Pillar depillaring working under the influence of dead load condition of voluminous and fragmented softcover of overburden dump material. It reports the modeling of a mine working through the FLAC 2D software under the Indian geo-mining conditions. The modeling results of an actual mine working under softcover were compared with that under the intact overburden condition to assess the influence of the soft overburden over the depillaring working. The modeling work involved progressive caving of the strata and the cyclic goaf filling following the model-simulated occurrence of main fall and periodic caving. Mohr-Coulomb Failure criteria along with a simplified strain-softening (MCSS) model was used to study the failure and caving mechanism. Salamon’s compaction model was used to simulate compaction and resultant stress recovery in the goaf material. Comparison of the model findings was done in terms of load on supports, abutment stress, and convergence, apart from the stress redistribution and failure mechanism. The load transfer mechanism of the soft overburden was also studied for an overall understanding of the strata behavior in such workings.
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Abbreviations
- FA:
-
Face advance
- HC:
-
Hardcover
- IC:
-
Intact condition
- IO:
-
Intact overburden
- IP:
-
Intact parting
- IR:
-
Immediate roof
- LR:
-
Loading roof
- MR:
-
Main roof
- SC:
-
Softcover condition
- SSC:
-
Settlement softcover condition
- SIC:
-
Settlement intact condition
- SR:
-
Settlement ratio
- ν :
-
Poisson’s ratio
- H :
-
Depth of cover
- β :
-
Coefficient of thermal conductivity
- E :
-
Elastic modulus
- G :
-
Geothermal gradient
- σ v :
-
Vertical stress
- σ h :
-
Horizontal stress
- σ c :
-
Compressive strength (MPa)
- σ t :
-
Tensile strength (MPa)
- c :
-
Cohesion (MPa)
- ϕ :
-
The angle of internal friction (°)
References
Indian Bureau of Mines (2018) Ministry of mines. Indian Minerals Yearbook 2018 (Part-III) Mineral Reviews: 57th edn
Singh R, Singh TN, Dhar BB (1995) Coal pillar loading in shallow mining conditions. Int J Rock Mech Min Sci Geomech Abstr 33(8):757–768. https://doi.org/10.1016/S0148-9062(96)00036-8
Van der Merwe JN (2006) Beyond Coalbrook: what did we learn? J S Afr Inst Min Metall 106:857–868
Kushwaha A, Singh SK, Tewari S, Sinha A (2010) Empirical approach for designing of support system in mechanized mining. Int J Rock Mech Min Sci 47(7):1063–1078. https://doi.org/10.1016/j.ijrmms.2010.06.001
Mandal PK, Das AJ, Kumar N, Bhattacharjee R, Tewari S, Kushwaha A (2018) Assessment of roof convergence during driving roadways in underground coal mines by continuous miner. Int J Rock Mech Min Sci 108:169–178. https://doi.org/10.1016/j.ijrmms.2018.06.001
Qian MG, Miao XX, Xu JL, Mao XB (2003) Study of key strata theory in ground control. China University of Mining and Technology
Kushwaha A, Banerjee G (2004) Exploitation of developed coal mine pillars by shortwall mining- a case example. Int J Rock Mech Min Sci 42(1):127–136. https://doi.org/10.1016/j.ijrmms.2004.08.004
Ju J, Xu J (2013) Structural characteristics of the key strata and the strata behavior of a fully mechanized longwall face with 7.0m height chocks. Int J Rock Mech Min Sci 58:46–54. https://doi.org/10.1016/j.ijrmms.2012.09.006
Wang F (2014) Overburden strata movement for the longwall mining of shallow seam under the gobs of room and pillar mining. In: Proceedings of the 33rd International Conference on Ground Control in Mining
Ju J, Xu J (2015) Surface stepped subsidence related to top-coal caving longwall mining of extremely thick coal seam under shallow cover. Int J Rock Mech Min Sci 78:27–35. https://doi.org/10.1016/j.ijrmms.2015.05.003
Wang C, Zhang C, Zhao X, Liao L, Zhang S (2018) Dynamic structural evolution of overlying strata during shallow coal seam longwall mining. Int J Rock Mech Min Sci 103:20–32. https://doi.org/10.1016/j.ijrmms.2018.01.014
Wang F, Jiang B, Chen S, Ren M (2019) Surface collapse control under thick unconsolidated layers by backfilling strip mining in coal mines. Int J Rock Mech Min Sci 113:268–277. https://doi.org/10.1016/j.ijrmms.2018.11.006
Singh KB (2000) Causes and remedial measures of pothole subsidence due to coal mining. J Sci Ind Res 59, 280–285
Lokhande RD, Murthy VMSR, Venkateswarlu V, Singh KB (2015) Assessment for pot hole subsidence risk for Indian coal mines. Int J Min Sci Technol 25(2):185–192. https://doi.org/10.1016/j.ijmst.2015.02.004
Yang W, Xia X (2018) Study of mining failure law of the weak and weathered composite roof in thin bedrock working face. J Geophys Eng 15(6):2370–2377. https://doi.org/10.1088/1742-2140/aacedf
Wang SR, Wu XG, Zhao YH, Hagan P, Cao C (2019) Evolution characteristics of composite pressure-arch in thin bedrock of overlying strata during shallow coal mining. Int J Appl Mech 11(3):1950030. https://doi.org/10.1142/S1758825119500303
Singh GSP (2004) Development of a model for cavability assessment in longwall panels in India. M tech Thesis, Department of Mining Engineering, Indian School of Mines, Dhanbad
Obert L, Duvall WI (1967) Rock mechanics and the design of structures in rock. Wiley, New York
Itasca (2011) Fast Lagrangian Analysis of Continua Ver 7.0 Two Dimension, User’s Guide, Minneapolis, USA
Sheorey PR (1994) A theory for in situ stresses in isotropic and transversely isotropic rock. Int J Rock Mech Min Sci Geomech Abstr 31:23–34. https://doi.org/10.1016/0148-9062(94)92312-4
Singh GSP, Singh UK (2009a) A numerical modeling approach for the assessment of progressive caving of strata and performance of the hydraulic powered supports. Comput Geotech 36(7):1142–1156. https://doi.org/10.1016/j.compgeo.2009.05.001
Singh GSP, Singh UK (2010a) Prediction of caving behavior of strata and optimum rating of hydraulic powered support for longwall workings. Int J Rock Mech Min Sci 47(1):1–16. https://doi.org/10.1016/j.ijrmms.2009.09.001
Singh GSP, Singh UK (2010b) Numerical modeling study of the effect of some critical parameters on caving behavior of strata and support performance in a longwall working. Rock Mech Rock Eng 43:475–489. https://doi.org/10.1007/s00603-009-0061-1
Li W, Bai J, Peng S, Wang X, Xu Y (2015) Numerical modeling for yield pillar design: a case study. Rock Mech Rock Eng 48:305–318. https://doi.org/10.1007/s00603-013-0539-8
Jiang L, Zhang P, Chen L, Hao Z, Sainoki A, Mitri HS, Wang Q (2017) Numerical approach for goaf-side entry layout and yield pillar design in fractured ground conditions. Rock Mech Rock Eng 50:3049–3071. https://doi.org/10.1007/s00603-017-1277-0
Wang M, Bai J, Li W, Wang X, Cao S (2015) Failure mechanism and control of deep goaf-side entry. Arab J Geol 8:9117–9131. https://doi.org/10.1007/s12517-015-1904-6
Zhang G, He F, Jia H, Lai Y (2017) Analysis of gateroad stability in relation to yield pillar size: a case study. Rock Mech Rock Eng 50:1263–1278. https://doi.org/10.1007/s00603-016-1155-1
Weng L, Luan H, Luan Y (2018) A numerical approach considering mining-induced fracture weakening and goaf compaction on surface subsidence. Geotech Geol Eng 37:283–294. https://doi.org/10.1007/s10706-018-0608-6
Kripakov NP, Beckett LA, Donato DA, Durr JS (1988) Computer-assisted mine design procedures for longwall mining. United States Department of the Interior, Report of the Investigations 9172: 1–38
Yavuz H (2004) An estimation method of cover pressure re-establishment distance and pressure distribution in the goaf of longwall coal mines. Int J Rock Mech Min Sci 41:193–205. https://doi.org/10.1016/S1365-1609(03)00082-0
Wang W, Jiang T, Wang Z, Ren M (2017) A analytical model for the cover stress re-establishment in the goaf after longwall caving mining. J South Afr Inst Min Metall 117:671–683. https://doi.org/10.17159/2411-9717/2017/v117n7a9
Singh GSP, Singh UK (2011) Assessment of goaf characteristics and compaction in longwall caving. Min Technol Trans Inst Min Metall (Sect A) 120(4):222–232. https://doi.org/10.1179/1743286311Y.0000000010
Peng SS (1984) Chiang HS. Wiley, Longwall Mining
Salamon MDG (1990a) Mechanism of caving in longwall coal mining. Rock mechanics contribution and challenges. In: Proceedings of the 31st US symposium of rock mechanics. Golden, Colorado, pp 161–168
Badr SA (2004) Numerical analysis of coal yield pillars at deep longwall mines. PhD thesis, Colorado School of Mines, Golden, CO, USA
Sahoo SK, Behera B, Yadav A, Singh GSP, Sharma SK (2019) Plain strain modeling of progressive goaf compaction in a depillaring working under partially destressed overburden. Geotechnical and Geological Engineering. Unpublished
Singh AK, Singh R, Maiti J, Rakesh K, Mandal PK (2011) Assessment of mining induced stress development over coal pillars during depillaring. Int J Rock Mech Min Sci 48(5):805–818. https://doi.org/10.1016/j.ijrmms.2011.04.004
Jena SK, Lokhande R, Thakur RP (2016) Strata control monitoring with convergence, trend analysis in conventional bord and pillar extraction: a case study of underground coal mining at SECL. In: Proceedings of the Recent Practices and Innovations in Mining Industry: 347-361
Reed G, Frith R (2017) An assessment of coal pillar system stability criteria based on a mechanistic evaluation of the interaction between coal pillars and the overburden. In: Proceedings of the 2017 Coal Operators’ Conference, University of Wollongong: 77-89
Frith R, Reed G, Jones A (2019) A causation mechanism for coalbursts during roadway development based on the major horizontal stress in coal, very specific structural geology causing a localised loss of effective coal confinement and Newtons’ second law. In: Proceedings of the 2019 Coal Operators’ Conference, University of Wollongong :297–320
Acknowledgments
The authors are thankful to the Head, Department of Mining Engineering, IIT (BHU) for providing adequate laboratory and computational facilities. Further, they express gratitude to the M/s. BCCL for providing the site details for carrying out this scientific study.
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Highlights
• Numerical simulation results depicted that the main roof experienced a more dynamic loading effect as compared to the immediate roof in the soft overburden condition.
• Cumulative displacement of the yielded main roof and immediate roof strata increased after the periodic weighting in the depillaring working.
• Settlement at the surface is highest than the goaf material due to deformation of the fractured hardcover in the soft overburden conditions.
• Rib pillars faced shear failure in the horizontal direction due to the rotational and sliding tendency of the yielded block of the overlying immediate roof.
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Sahoo, S.K., Singh, G.S.P., Sharma, S.K. et al. Numerical Modeling Study of the Influence of Softcover on Strata and Support Behavior in a Bord and Pillar Depillaring Working. Mining, Metallurgy & Exploration 37, 1151–1168 (2020). https://doi.org/10.1007/s42461-020-00246-1
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DOI: https://doi.org/10.1007/s42461-020-00246-1