Compaction characteristics of the caving zone in a longwall goaf: a review

  • Cun ZhangEmail author
  • Shihao Tu
  • YiXin Zhao
Original Article


Broken rock and coal—residual coal, plus material from the immediate roof and overlying strata—fill in the goaf, in an area termed the caving zone. Due to its high porosity and permeability, the caving zone contains gas and water, which may have originated from the mined coal seam, the adjacent unmined coal seam, or from any aquifer or surface river. Thus, studying the compaction characteristics of the caving zone can help understand gas and mine water drainage and identify steps to prevent spontaneous combustion of residual coal. The stability characteristics of the caving zone after mining are affect surface subsidence, as well as water and gas build-up and use. The caving zone is a potential underground storage of greenhouse gases. Therefore, the time–space relationship of caving zone compaction characteristics in the goaf has become an area for research focus in recent years; in this study, the formation, height determination, and compaction characteristics of a caving zone are examined. Reduction in block size and rearrangement of the fill are the main factors affecting the compaction process, as re-crushing and rearrangement of the broken coal and rock mass affect the secant modulus and pore size of the caving zone, causing the secant modulus to gradually increase and pore size to decrease. This in turn affects the macroscopic stress–strain curve and seepage characteristics of the caving zone. The strength and fracturing mode of the caving blocks are the main factors affecting the re-crushing and rearrangement of the caving blocks. The applicability and reliability of present research results and research methods are analyzed and the focus areas for future studies are identified. Using a combination of research methods, including theoretical analysis, laboratory testing, numerical simulation, and field measurement, the compaction characteristics of a caving zone in longwall goaf can be accurately calculated.


Caving zone Compaction characteristics Strain Stress Permeability Porosity 



Financial support for this work was provided by the Beijing Municipal Natural Science Foundation (No. 8184082), the National Natural Science Foundation of China (No. 51374200) and the Yue Qi Distinguished Scholar Project, China University of Mining & Technology, Beijing..


  1. Bai M, Kendorski FS, Van Roosendaal DJ (1995) Chinese and North American high-extraction underground coal mining strata behavior and water protection experience and guidelines (No. CONF-950811–). West Virginia Univ., MorgantownGoogle Scholar
  2. Bai QS, Tu SH, Yuan Y, Wang FT (2013) Back analysis of mining induced responses on the basis of goaf compaction theory. J China Univ Min Technol 42(3):355–361Google Scholar
  3. Bai Q, Tu S, Wang F, Zhang C (2017) Field and numerical investigations of gateroad system failure induced by hard roofs in a longwall top coal caving face. Int J Coal Geol 173:176–199Google Scholar
  4. Baptiste N, Chapuis RP (2015) What maximum permeability can be measured with a monitoring well? Eng Geol 184:111–118Google Scholar
  5. Barrash W, Clemo T, Fox JJ, Johnson TC (2006) Field, laboratory, and modeling investigation of the skin effect at wells with slotted casing, boise hydrogeophysical research site. J Hydrol 326(1):181–198Google Scholar
  6. Bauer E (2009) Hypoplastic modelling of moisture-sensitive weathered rockfill materials. Acta Geotech 4(4):261Google Scholar
  7. Booth CJ, Greer CB (2011) Application of MODFLOW using TMR and discrete-step modification of hydraulic properties to simulate the hydrogeologic impact of longwall mining subsidence on overlying shallow aquifers. Proc, Mine Water—Managing the Challenges, Aachen, pp 211–215Google Scholar
  8. Cao DT, Li WP (2014) Estimation method for height of featured zone with water flow in coal mining area. Chin J Geol Hazard Control 25(1):63–69Google Scholar
  9. Chen W, Qiu T (2011) Numerical simulations for large deformation of granular materials using smoothed particle hydrodynamics method. Int J Geomech 12(2):127–135Google Scholar
  10. Chen D, Pan Z, Ye Z (2015a) Dependence of gas shale fracture permeability on effective stress and reservoir pressure: model match and insights. Fuel 139:383–392Google Scholar
  11. Chen LF, Zhu JG, Yin JH (2015b) Numerical simulations of mechanical characteristics of coarse grained soil with different aspect ratios of tri-axial test. J Central South Univ 46(7):2643–2649Google Scholar
  12. Chen D, Pan Z, Ye Z, Hou B, Wang D, Yuan L (2016) A unified permeability and effective stress relationship for porous and fractured reservoir rocks. J Nat Gas Sci Eng 29:401–412Google Scholar
  13. Cheng WD, Xie JW, Wang GY, Xie PS (2009) Comparison of strata movement between section and slicing of top coal mining in steep and thick seams. J China Coal Soc 34(4):478–481Google Scholar
  14. Cheng G, Ma T, Tang C, Liu H, Wang S (2017) A zoning model for coal mining-induced strata movement based on microseismic monitoring. Int J Rock Mech Min Sci 94:123–138Google Scholar
  15. Chu T, Yu M, Jiang D (2017) Experimental investigation on the permeability evolution of compacted broken coal. Transp Porous Media 116(2):847–868Google Scholar
  16. Deng KZ, Tan ZX, Zhang HZ, Fan HD, Zhang LY (2012) Research on calculating method of residual subsidence of longwall goaf. J China Coal Soc 37(10):1601–1605Google Scholar
  17. Esterhuizen GS, Karacan CO (2005) Development of numerical models to investigate permeability changes and gas emission around longwall mining panel. In: Alaska Rocks 2005, The 40th US symposium on rock mechanics (USRMS). American Rock Mechanics AssociationGoogle Scholar
  18. Fan L, Liu S (2017) A conceptual model to characterize and model compaction behavior and permeability evolution of broken rock mass in coal mine gobs. Int J Coal Geol 172:60–70Google Scholar
  19. Feng GR, Yan YG, Yang SS, Zhang BS, Zhai YD, Kang LX (2009) Analysis on the damage zone of overlying strata and safety layer distance on the upward mining above the longwall goaf. J China Coal Soc 34(8):1032–1036Google Scholar
  20. Fu Y, Song XM, Xing PW (2010) Study of the mining height of caving zone in large mining height and super-long face of shallow seam. J Min Saf Eng 27(2):190–194Google Scholar
  21. Guo G, Wang Y, Ma Z (2004) A new method for ground subsidence control in coal mining. J China Univ Min Technol 33(2):150–153Google Scholar
  22. Guo H, Adhikary DP, Craig MS (2009) Simulation of mine water inflow and gas emission during longwall mining. Rock Mech Rock Eng 42(1):25–51Google Scholar
  23. Guo H, Qin J, Qu Q (2012) CFD Investigation of goaf flow of methane released from unmined adjacent coal seams. In: Ninth International Conference on CFD in the Minerals and Process Industries. Melbourne, pp 1–6Google Scholar
  24. Guo H, Todhunter C, Qu Q, Qin Z (2015) Longwall horizontal gas drainage through goaf pressure control. Int J Coal Geol 150:276–286Google Scholar
  25. Gupta AK, Paul B (2015) A review on utilisation of coal mine overburden dump waste as underground mine filling material: a sustainable approach of mining. Int J Min Mineral Eng 6(2):172–186Google Scholar
  26. Hu Q, Liang YP, Liu JZ (2007) CFD simulation of goaf gas flow patterns. J Coal Sci Eng 32(7):719–723Google Scholar
  27. Jin LZ, Yao W, Zhang J (2010) CFD simulation of gas seepage regularity in goaf. J China Coal Soc 35(9):1476–1480Google Scholar
  28. Jozefowicz RR (1997) The post-failure stress-permeability behaviour of coal measure rocks (Doctoral dissertation, University of Nottingham)Google Scholar
  29. Ju JF, Xu JL, Zhu WB (2017) Storage capacity of underground reservoir in the chinese western water-short coalfield. J China Coal Soc 42(2):381–387Google Scholar
  30. Kang H, Lou J, Gao F et al (2018) A physical and numerical investigation of sudden massive roof collapse during longwall coal retreat mining. Int J Coal Geol 188:25–36Google Scholar
  31. Karacan C (2009a) Reconciling longwall gob gas reservoirs and venthole production performances using multiple rate drawdown well test analysis. Int J Coal Geol 80(3):181–195Google Scholar
  32. Karacan C (2009b) Forecasting gob gas venthole production performances using intelligent computing methods for optimum methane control in longwall coal mines. Int J Coal Geol 79(4):131–144Google Scholar
  33. Karacan C (2010) Prediction of porosity and permeability of caved zone in longwall gobs. Transp Porous Media 82(2):413–439Google Scholar
  34. Karacan C (2015) Analysis of gob gas venthole production performances for strata gas control in longwall mining. Int J Rock Mech Min Sci 79:9–18Google Scholar
  35. Karacan C, Esterhuizen GS, Schatzel SJ, Diamond WP (2007) Reservoir simulation-based modeling for characterizing longwall methane emissions and gob gas venthole production. Int J Coal Geol 71(2):225–245Google Scholar
  36. Karfakis MG, Bowman CH, Topuz E (1996) Characterization of coal-mine refuse as backfilling material. Geotech Geol Eng 14(2):129–150Google Scholar
  37. Koenig RA, Schraufnagel RA (1987) Application of the slug test in coalbed methane testing. Paper 8743:195–205Google Scholar
  38. Lan ZQ, Zhang GS (2007) Numerical simulation of gas concentration field in multi-source and multi-congruence goaf. J China Coal Soc 32(4):396–401Google Scholar
  39. Lei HT (2015) Study on new type of caving zone height calculation method. Coal Chem Ind 38(9):1–3Google Scholar
  40. Li XY, Logan BE (2001) Permeability of fractal aggregates. Water Res 35(14):3373–3380Google Scholar
  41. Li JM, Fei L, Wang HY, Zhou W, Liu HL, Zhao Q, Li GZ, Wang B (2008) Desorption characteristics of coalbed methane reservoirs and affecting factors. Pet Explor Dev 35(1):52–58Google Scholar
  42. Li M, Zhang J, Zhou N, Huang Y (2017) Effect of particle size on the energy evolution of crushed waste rock in coal mines. Rock Mech Rock Eng 50(5):1347–1354Google Scholar
  43. Liang YT, Zhang TF, Wang SG, Sun JP (2009) Heterogeneous model of porosity in gobs and its airflow field distribution. J China Coal Soc 34(9):1203–1207Google Scholar
  44. Liang B, Wang B, Jiang L, Li G, Li C (2016) Broken expand properties of caving rock in shallow buried goaf. J China Univ Min Technol 45(3):475–482Google Scholar
  45. Liu J, Hu H (2013) Pfc analysis of the uplift bearing capacity of plate anchors in sand. Chin J Comput Mech 30(5):677–638Google Scholar
  46. Liu Z, Zhou N, Zhang J (2013) Random gravel model and particle flow based numerical biaxial test of solid backfill materials. Int J Min Sci Technol 23(4):463–467Google Scholar
  47. Liu W, Li Y, Yang C, Daemen JJ, Yang Y, Zhang G (2015) Permeability characteristics of mudstone cap rock and interlayers in bedded salt formations and tightness assessment for underground gas storage caverns. Eng Geol 193:212–223Google Scholar
  48. Liu Y, Shao S, Wang X, Chang L, Cui G, Zhou F (2016) Gas flow analysis for the impact of gob gas ventholes on coalbed methane drainage from a longwall gob. J Nat Gas Sci Eng 36:1312–1325Google Scholar
  49. Ma ZG, Miao XX, Zhen ZQ, Li YS (2009) Experimental study of permeability of broken coal. Rock Soil Mech 30(4):985–988Google Scholar
  50. McKee CR, Bumb AC, Koenig RA (1988) Stress-dependent permeability and porosity of coal and other geologic formations. SPE Form Eval 3(01):81–91Google Scholar
  51. Meng Z, Shi X, Liu S, Tian Y, Li C (2016a) Evaluation model of CBM resources in abandoned coal mine and its application. J China Coal Soc 41(3):537–544Google Scholar
  52. Meng ZP, Zhang J, Shi XC, Tian YD, Li C (2016b) Calculation model of rock mass permeability in coal mine goaf and its numerical simulation analysis. J China Coal Soc 41(8):1997–2005Google Scholar
  53. Miao XX, Zhang JX, Feng MM (2008) Waste-filling in fully-mechanized coal mining and its application. J China Univ Min Technol 18(4):479–482Google Scholar
  54. Oldecop LA, Alonso EE (2004) Testing rockfill under relative humidity control. Geotech Test J 27(3):269–278Google Scholar
  55. Palchik V (2003) Formation of fractured zones in overburden due to longwall mining. Environ Geol 44(1):28–38Google Scholar
  56. Palchik V (2010) Experimental investigation of apertures of mining-induced horizontal fractures. Int J Rock Mech Min Sci 47(3):502–508Google Scholar
  57. Pappas DM, Mark C (1993) Behavior of simulated longwall gob material, vol 9458. US Department of the Interior, Bureau of Mines, pp 25–27Google Scholar
  58. Pryor WA (1973) Permeability-porosity patterns and variations in some Holocene sand bodies. AAPG Bull 57(1):162–189Google Scholar
  59. Qin Z, Yuan L, Guo H, Qu Q (2015a) Investigation of longwall goaf gas flows and borehole drainage performance by CFD simulation. Int J Coal Geol 150:51–63Google Scholar
  60. Qin W, Xu J, Hu G (2015b) Numerical simulation of abandoned Gob methane drainage through surface vertical wells. PLoS One 10(5):e0125963Google Scholar
  61. Ryder JA, Wagner H (1978) 2D analysis of backfill as a means of reducing energy release rates at depth. Unpubl. Res. report. Chamb. Mines South Africa, JohannesbgGoogle Scholar
  62. Salamon MDG (1991) Displacements and stresses induced by longwall mining in coal. In: 7th ISRM congress, International society for rock mechanics, Aachen, GermanyGoogle Scholar
  63. Schatzel SJ, Krog RB, Dougherty H (2017) Methane emissions and airflow patterns on a longwall face: potential influences from longwall gob permeability distributions on a bleederless longwall panel. Trans Soc Min Metall Explor 342(1):51Google Scholar
  64. Seidle JP, Jeansonne DJ, Erickson DJ (1992) Application of matchstick geometry to stress dependent permeability in coals. In: SPE rocky mountain regional meeting, Paper SPE 24361, Casper, Wyoming, pp 433–444Google Scholar
  65. Shu DM, Chamberlain JA, Lakshmanan CC, White N (1995) Estimation of in-situ coal permeability and modeling of methane pre-drainage from in-seam holes. In: International symposium on cum workshop on management and control of high gas emissions and outbursts in underground coal mines, Wollongong, Australia, pp 303–310Google Scholar
  66. Sitharam TG, Vinod JS (2010) Evaluation of shear modulus and damping ratio of granular materials using discrete element approach. Geotech Geol Eng 28(5):591–601Google Scholar
  67. Su C, Gu M, Tang X, Guo W (2012) Experiment study of compaction characteristics of crushed stones from coal seam roof. Chin J Rock Mech Eng 31(1):2012–2011Google Scholar
  68. Sun QX, Mou Y, Yang XL (2013) Study on “two-zone” height of overlying of fully-mechanized technology with high mining height at Hongliu coal mine. J China Coal Soc 38(S2):283–286Google Scholar
  69. Tang M, Jiang B, Zhang R, Yin Z, Dai G (2016) Numerical analysis on the influence of gas extraction on air leakage in the gob. J Nat Gas Sci Eng 33:278–286Google Scholar
  70. Ti Z, Qin H, Cao Y (2014) DM-L optimization model of height of water flowing fractured zone based on sensitivity analysis. J Huazhong Normal Univ 48(5):673–676Google Scholar
  71. Tu S, Zhang C, Yang G, Bai Q, Yan R (2016) Research on permeability evolution law of goaf and pressure-relief mining effect. J Min Saf Eng 33(4):571–577Google Scholar
  72. Wang DS (2011) Simulation of gas flow rule at three dimensional drainage under close distance seam group mining. J China Coal Soc 36(1):86–90Google Scholar
  73. Wang M (2013) Simulation of compression test on gangue by pfc3d. Chin J Rock Mech Eng 32(7):1350–1357Google Scholar
  74. Wang ZQ, Zhao JL, Li ZQ (2013) Determination of height of “three zone” in the stope with stagger position and internal misaligned roadway layout. J Min Saf Eng 30(2):231–236Google Scholar
  75. Wang B, Liang B, Jiang L, Li G, Li C (2015) Research on fractal calculation and application of water storage in void of caving rock in the goaf. Chin J Rock Mech Eng 34(7):1444–1451Google Scholar
  76. Wang F, Tu S, Zhang C, Zhang Y, Bai Q (2016) Evolution mechanism of water-flowing zones and control technology for longwall mining in shallow coal seams beneath gully topography. Environ Earth Sci 75(19):1309Google Scholar
  77. Wang F, Zhang C, Liang N (2017) Gas permeability evolution mechanism and comprehensive gas drainage technology for thin coal seam mining. Energies 10(9):1382Google Scholar
  78. Whittles DN, Lowndes IS, Kingman SW, Yates C, Jobling S (2006) Influence of geotechnical factors on gas flow experienced in a UK longwall coal mine panel. Int J Rock Mech Min Sci 43(3):369–387Google Scholar
  79. Whittles DN, Lowndes IS, Kingman SW, Yates C, Jobling S (2007) The stability of methane capture boreholes around a long wall coal panel. Int J Coal Geol 71(2):313–328Google Scholar
  80. Wu RL (2013) Effects of key stratum on the scope of the “three zones” of gas pressure relief and migration in coal seam group mining. J China Coal Soc 38(6):924–929(6)Google Scholar
  81. Wu F, Yang J, Yu B, Chen X (2014) Determination of the roof caving heights of thick and extra thick coal seams. J China Univ Min Technol 43(5):765–772Google Scholar
  82. Xia T, Wang X, Zhou F, Kang J, Liu J, Gao F (2015) Evolution of coal self-heating processes in longwall gob areas. Int J Heat Mass Transf 86:861–868Google Scholar
  83. Xin GA, Zhang YB, Zhu HJ (2011) Application study on gas extraction technology by surface borehole. J Anhui Univ Sci Technol 31(4):65–70Google Scholar
  84. Xu Q, Yang SQ, Wang C, Chu TX, Wei MA, Huang J (2010) Numerical simulation of gas flow law in stope under stereo gas drainage. J Min Saf Eng 27(1):66–70Google Scholar
  85. Xu M, Song E, Chen J (2012) A large triaxial investigation of the stress-path-dependent behavior of compacted rockfill. Acta Geotech 7(3):167–175Google Scholar
  86. Yang Y, Liang P (2013) The detection technology of goaf overburden rock damage of based on EH4 electromagnetic imaging system. Chin J Geol Hazard Control 24(3):68–71Google Scholar
  87. Yang TH, Chen SK, Zhu WC, Huo ZG, Jiang WZ (2009) Numerical model of nonlinear flow-diffusion for gas mitigation in goaf and atmosphere. J China Coal Soc 34(6):771–777Google Scholar
  88. Yavuz H (2004) An estimation method for cover pressure re-establishment distance and pressure distribution in the goaf of longwall coal mines. Int J Rock Mech Min Sci 41(2):193–205Google Scholar
  89. Yu B, Chen Z, Ding Q, Wang L (2016) Non-Darcy flow seepage characteristics of saturated broken rocks under compression with lateral constraint. Int J Min Sci Technol 26(6):1145–1151Google Scholar
  90. Yu B, Chen Z, Dai Y, Xu M, Wei J (2018) Particle size distribution and energy dissipation of saturated crushed sandstone under compaction. J Min Saf Eng 35(1):197–204Google Scholar
  91. Yuan L, Smith AC (2007) Computational fluid dynamics modeling of spontaneous heating in longwall gob areas. Trans Soc Min Metall Explor Inc 322:37Google Scholar
  92. Zhang HW, Zhu ZJ, Huo BJ, Song WH (2013) Water flowing fractured zone height prediction based on improved foa-svm. China Saf Sci J 23(10):9Google Scholar
  93. Zhang HW, Zhu ZJ, Huo LJ, Chen Y, Huo BJ (2014) Overburden failure height of superhigh seam by fully mechanized caving method. J China Coal Soc 39(5):816–821Google Scholar
  94. Zhang C, Tu S, Bai Q, Yang G, Zhang L (2015a) Evaluating pressure-relief mining performances based on surface gas venthole extraction data in longwall coal mines. J Nat Gas Sci Eng 24:431–440Google Scholar
  95. Zhang C, Tu S, Yuan Y, Bai Q (2015b) Numerical simulation of surface gas venthole extraction in pressure relief mining. J China Coal Soc 40(S2):392–400Google Scholar
  96. Zhang L, Zhang C, Tu S, Tu H, Wang C (2016a) A study of directional permeability and gas injection to flush coal seam gas testing apparatus and method. Transp Porous Media 111(3):573–589Google Scholar
  97. Zhang C, Tu S, Zhang L, Bai Q, Yuan Y, Wang F (2016b) A methodology for determining the evolution law of gob permeability and its distributions in longwall coal mines. J Geophys Eng 13(2):181–193Google Scholar
  98. Zhang C, Tu S, Zhang L, Wang F, Bai Q, Tu H (2016c) The numerical simulation of permeability rules in protective seam mining. Int J Oil Gas Coal Technol 13(3):243–259Google Scholar
  99. Zhang C, Tu S, Chen M, Zhang L (2017a) Pressure-relief and methane production performance of pressure relief gas extraction technology in the longwall mining. J Geophys Eng 14(1):77–89Google Scholar
  100. Zhang C, Tu S, Zhang L (2017b) Analysis of broken coal permeability evolution under cyclic loading and unloading conditions by the model based on the hertz contact deformation principle. Transp Porous Media 119(3):739–754Google Scholar
  101. Zhao Y, Zhang J, Chou CL, Li Y, Wang Z, Ge Y (2008) Trace element emissions from spontaneous combustion of gob piles in coal mines, Shanxi, China. Int J Coal Geol 73(1):52–62Google Scholar
  102. Zhou F, Xia T, Wang X, Zhang Y, Sun Y, Liu J (2016) Recent developments in coal mine methane extraction and utilization in China: a review J Nat Gas Sci Eng 31:437–458Google Scholar
  103. Zhu G, Xu Z, Chen X, Ying G (2014) Study of influence functions of surface residual movement and deformation above old goaf. Chin J Rock Mech Eng 33(10):1962–1970Google Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Beijing Key Laboratory for Precise Mining of Intergrown Energy and ResourcesChina University of Mining and TechnologyBeijingChina
  2. 2.School of Resource and Safety EngineeringChina University of Mining and TechnologyBeijingChina
  3. 3.School of Mines, Key Laboratory of Deep Coal Resource Ministry of Education of ChinaChina University of Mining and TechnologyXuzhouChina

Personalised recommendations