Laboratory In Situ CT Observation of the Evolution of 3D Fracture Networks in Coal Subjected to Confining Pressures and Axial Compressive Loads: A Novel Approach

  • Yang Ju
  • Chaodong Xi
  • Yang Zhang
  • Lingtao Mao
  • Feng Gao
  • Heping Xie
Original Paper


Accurate characterisation of the three-dimensional (3D) fracture network of coal is of vital significance to enhancing coal seam permeability during simultaneous extraction of deep coal and methane resources. The limitations of traditional experimental methods prevent direct in situ observation and characterisation of the 3D fracture network and its evolution during loading processes. This study presents a novel approach that incorporates computed tomography and servo-controlled triaxial loading techniques to accomplish the laboratory in situ observation of the continuous evolution of 3D fracture networks inside coal samples which were subject to confining pressures and axial compressive loads. Spatial growth and morphologies of the interior fractures at various loading stages were captured in situ and extracted using imaging processing algorithms. The 3D fracture networks observed at different loading stages were quantitatively characterised using fractal theory and compared to evaluate the influences of confining pressures and vertical loads on their evolution. The results indicated that the original existing fractures of coal closed when the specimens were subject to confining pressures and vertical compressive deformation were in the linear elastic stage. Load-induced fractures expanded notably only when the axial compressive load reached the maximum value. The fractal dimension of the 3D fracture network tended to decrease initially and subsequently increased during the loading process, which reflects the evolutionary characteristics of coal fractures from a closed to an expanded state.


Three-dimensional fracture networks Laboratory in situ CT observation Fracture evolution Loading processes Confining pressures Fractal dimensions 

List of symbols


Fractal sets


Box-counting fractal dimensions


The side length of covering boxes


Grid size of the kth covering


Grid size of the (k + 1)th covering

Nδ (F)

Number of boxes covering the fractal set F



The authors sincerely appreciate the constructive and valuable comments from the editors and anonymous reviewers to help improve this manuscript. The authors also gratefully acknowledge financial support from the State Key Research Development Program of China (Grant no. 2016YFC0600705), the National Natural Science Foundation of China (Grant nos. 51674251, 51727807, 51374213), the National Major Project for Science and Technology (Grant no. 2017ZX05049003-006), the National Natural Science Fund for Distinguished Young Scholars of China (Grant no. 51125017), Fund for Innovative Research and Development Group Program of Jiangsu Province (Grant no. 2014-27), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (Grant no. PAPD 2014).


  1. Adhikary DP, Guo H (2015) Modelling of longwall mining-induced strata permeability change. Rock Mech Rock Eng 48:345–359. CrossRefGoogle Scholar
  2. Ai T, Zhang R, Zhou HW, Pei JL (2014) Box-counting methods to directly estimate the fractal dimension of a rock surface. Appl Surf Sci 314:610–621. CrossRefGoogle Scholar
  3. Almeida G, Leclerc S, Perre P (2008) NMR imaging of fluid pathways during drainage of softwood in a pressure membrane chamber. Int J Multiph Flow 34:312–321. CrossRefGoogle Scholar
  4. Bai X, Ding H, Lian J et al (2017) Coal production in China: past, present, and future projections. Int Geol Rev. Google Scholar
  5. Boehlert CJ, Cowen CJ, Tamirisakandala S, Mceldowney DJ, Miracle DB (2015) In situ scanning electron microscopy observations of tensile deformation in a boron-modified Ti–6Al–4V alloy. Scripta Mater 55:465–468CrossRefGoogle Scholar
  6. Cai YD, Liu D, Mathews JP et al (2014) Permeability evolution in fractured coal—combining triaxial confinement with X-ray computed tomography, acoustic emission and ultrasonic techniques. Int J Coal Geol 122:91–104. CrossRefGoogle Scholar
  7. Charkaluk E, Bigerelle M, Iost A (1998) Fractals and fracture. Eng Fract Mech 61:119–139. CrossRefGoogle Scholar
  8. Cheng YP, Wang L, Zhang XL (2011) Environmental impact of coal mine methane emissions and responding strategies in China. Int J Greenh Gas Con 5:157–166. CrossRefGoogle Scholar
  9. Cnudde V, Boone MN (2013) High-resolution X-ray computed tomography in geosciences: a review of the current technology and applications. Earth-Sci Rev 123:1–17. CrossRefGoogle Scholar
  10. Cnudde V, Masschaele B, Dierick M, Vlassenbroeck J, Van Hoorebeke L, Jacobs P (2006) Recent progress in X-ray CT as a geosciences tool. Appl Geochem 21:826–832. CrossRefGoogle Scholar
  11. Díaz Aguado MB, González Nicieza C (2007) Control and prevention of gas outbursts in coal mines, Riosa–Olloniego coalfield, Spain. Int J Coal Geol 69:253–266. CrossRefGoogle Scholar
  12. Espinoza DN, Shovkun I, Makni O, Lenoir N (2016) Natural and induced fractures in coal cores imaged through X-ray computed microtomography—impact on desorption time. Int J Coal Geol 154:165–175. CrossRefGoogle Scholar
  13. Falconer K (2003) Fractal geometry: mathematical foundations and applications, 3rd edn. Wiley, New YorkCrossRefGoogle Scholar
  14. Giffin S, Littke R, Klaver J, Urai JL (2013) Application of BIB–SEM technology to characterize macropore morphology in coal. Int J Coal Geol 114:85–95. CrossRefGoogle Scholar
  15. Hirono T, Takahashi M, Nakashima S (2003) In situ visualization of fluid flow image within deformed rock by X-ray CT. Eng Geol 70:37–46. CrossRefGoogle Scholar
  16. Hou H et al (2017) Evaluation and genetic analysis of coal structures in deep Jiaozuo Coalfield, northern China: investigation by geophysical logging data. Fuel 209:552–566. CrossRefGoogle Scholar
  17. Jiang JY, Cheng YP, Wang L, Li W, Wang L (2011) Petrographic and geochemical effects of sill intrusions on coal and their implications for gas outbursts in the Wolonghu Mine, Huaibei Coalfield, China. Int J Coal Geol 88:55–66. CrossRefGoogle Scholar
  18. Jiang L, Nishizawa O, Zhang Y, Park H, Xue Z (2016) A novel high-pressure vessel for simultaneous observations of seismic velocity and in situ CO2 distribution in a porous rock using a medical X-ray CT scanner. J Appl Geophys 135:67–76. CrossRefGoogle Scholar
  19. Ju Y, Xing M, Sun H (2013) Computer program for extracting and analyzing fractures in rocks and concretes. Software Copyright Registration #0530646, Beijing (in Chinese)Google Scholar
  20. Ju Y, Zheng JT, Epstein M, Sudak L, Wang JB, Zhao X (2014) 3D numerical reconstruction of well-connected porous structure of rock using fractal algorithms. Comput Method Appl Mech Eng 279:212–226. CrossRefGoogle Scholar
  21. Ju Y, Wang L, Xie HP, Ma GW, Zheng ZM, Mao LT (2017a) Visualization and transparentization of the structure and stress field of aggregated geomaterials through 3D printing and photoelastic techniques. Rock Mech Rock Eng 50:1383–1407. CrossRefGoogle Scholar
  22. Ju Y, Zhang Q, Zheng J, Chang C, Xie H (2017b) Fractal model and lattice Boltzmann method for characterization of non-darcy flow in rough fractures. Sci Rep 7:41380. CrossRefGoogle Scholar
  23. Ju Y, Zhang Q, Zheng J, Wang J, Chang C, Gao F (2017c) Experimental study on CH4 permeability and its dependence on interior fracture networks of fractured coal under different excavation stress paths. Fuel 202:483–493. CrossRefGoogle Scholar
  24. Kang H, Zhang X, Si L, Wu Y, Gao F (2010) In-situ stress measurements and stress distribution characteristics in underground coal mines in China. Eng Geol 116:333–345. CrossRefGoogle Scholar
  25. Karacan CÖ, Olea RA (2014) Inference of strata separation and gas emission paths in longwall overburden using continuous wavelet transform of well logs and geostatistical simulation. J Appl Geophys 105:147–158. CrossRefGoogle Scholar
  26. Karacan CO, Ruiz FA, Cote M, Phipps S (2011) Coal mine methane: a review of capture and utilization practices with benefits to mining safety and to greenhouse gas reduction. Int J Coal Geol 86:121–156. CrossRefGoogle Scholar
  27. Karpyn ZT, Alajmi A, Radaelli F, Halleck PM, Grader AS (2009) X-ray CT and hydraulic evidence for a relationship between fracture conductivity and adjacent matrix porosity. Eng Geol 103:139–145. CrossRefGoogle Scholar
  28. Krohn CE, Thompson AH (1986) Fractal sandstone pores: automated measurements using scanning-electron-microscope images. Phys Rev B 33:6366–6374CrossRefGoogle Scholar
  29. Kumar H et al (2011) Inducing fractures and increasing cleat apertures in a bituminous coal under isotropic stress via application of microwave energy. Int J Coal Geol 88:75–82. CrossRefGoogle Scholar
  30. Liu P, Ju Y, Ranjith PG, Zheng ZM, Chen JL (2016) Experimental investigation of the effects of heterogeneity and geostress difference on the 3D growth and distribution of hydro-fracturing cracks in unconventional reservoir rocks. J Nat Gas Sci Eng 35:541–554. CrossRefGoogle Scholar
  31. Liu M, Chen M, He G (2017) The origin and prospect of billion-ton coal production capacity in China. Resour Conserv Recycl 125:70–85. CrossRefGoogle Scholar
  32. Macholdt DS et al (2015) Microanalytical methods for in situ high-resolution analysis of rock varnish at the micrometer to nanometer scale. Chem Geol 411:57–68. CrossRefGoogle Scholar
  33. Mandelbrot BB (1983) The fractal geometry of nature. W.H. Freeman, New YorkGoogle Scholar
  34. Mathews JP, Campbell QP, Xu H, Halleck P (2017) A review of the application of X-ray computed tomography to the study of coal. Fuel 209:10–24. CrossRefGoogle Scholar
  35. Nicula S, Lyne A (2001) NMR imaging studies on drilling fluid induced rock damage. Magn Reson Imaging 19:579CrossRefGoogle Scholar
  36. O’Brien G, Gu Y, Adair BJI, Firth B (2011) The use of optical reflected light and SEM imaging systems to provide quantitative coal characterisation. Miner Eng 24:1299–1304. CrossRefGoogle Scholar
  37. Peng RD, Yang YC, Ju Y, Mao LT, Yang YM (2011) Computation of fractal dimension of rock pores based on gray CT images. Chin Sci Bull 56:3346–3357. CrossRefGoogle Scholar
  38. Pradhan S, Stroisz AM, Fjaer E, Stenebraten JF, Lund HK, Sonstebo EF (2015) Stress-induced fracturing of reservoir rocks: acoustic monitoring and CT image analysis. Rock Mech Rock Eng 48:2529–2540. CrossRefGoogle Scholar
  39. Qian MG, Miao XX, Xu JL (2007) Green mining of coal resources harmonizing with environment. J China Coal Soc 32:1–7 (In Chinese) Google Scholar
  40. Schatzel SJ, Karacan CÖ, Dougherty H, Goodman GVR (2012) An analysis of reservoir conditions and responses in longwall panel overburden during mining and its effect on gob gas well performance. Eng Geol 127:65–74. CrossRefGoogle Scholar
  41. Sell K et al (2016) On the path to the digital rock physics of gas hydrate-bearing sediments—processing of in situ synchrotron-tomography data. Solid Earth 7:1243–1258. CrossRefGoogle Scholar
  42. Sun WJ, Feng YY, Jiang CF, Chu W (2015) Fractal characterization and methane adsorption features of coal particles taken from shallow and deep coalmine layers. Fuel 155:7–13. CrossRefGoogle Scholar
  43. Sun W, Wu A, Hou K, Yang Y, Liu L, Wen Y (2016) Real-time observation of meso-fracture process in backfill body during mine subsidence using X-ray CT under uniaxial compressive conditions. Constr Build Mater 113:153–162. CrossRefGoogle Scholar
  44. Sun W, Hou K, Yang Z, Wen Y (2017) X-ray CT three-dimensional reconstruction and discrete element analysis of the cement paste backfill pore structure under uniaxial compression. Constr Build Mater 138:69–78. CrossRefGoogle Scholar
  45. Wang R, Pavlin T, Rosen MS, Mair RW, Cory DG, Walsworth RL (2005) Xenon NMR measurements of permeability and tortuosity in reservoir rocks. Magn Reson Imaging 23:329–331. CrossRefGoogle Scholar
  46. Wang SG, Elsworth D, Liu JS (2011) Permeability evolution in fractured coal: The roles of fracture geometry and water-content. Int J Coal Geol 87:13–25. CrossRefGoogle Scholar
  47. Watanabe N et al (2012) Geologic core holder with a CFR PEEK body for the X-ray CT-based numerical analysis of fracture flow under confining pressure. Rock Mech Rock Eng 46:413–418. CrossRefGoogle Scholar
  48. Wennberg OP, Rennan L, Basquet R (2009) Computed tomography scan imaging of natural open fractures in a porous rock; geometry and fluid flow. Geophys Prospect 57:239–249. CrossRefGoogle Scholar
  49. Xia TQ, Zhou FB, Wang XX, Zhang YF, Li YM, Kang JH, Liu JS (2016) Controlling factors of symbiotic disaster between coal gas and spontaneous combustion in longwall mining gobs. Fuel 182:886–896. CrossRefGoogle Scholar
  50. Xie H (1993) Fractals in rock mechanics. A.A. Balkema, RotterdamGoogle Scholar
  51. Xie H, Zhao X, Liu J, Zhang R, Xue D (2012) Influence of different mining layouts on the mechanical properties of coal. Int J Min Sci Technol 22:749–755. CrossRefGoogle Scholar
  52. Xie HP, Zhou HW, Xue DJ, Gao F (2014) Theory, technology and engineering of simultaneous exploitation of coal and gas in China. J China Coal Soc 39:1391–1397 (In Chinese) Google Scholar
  53. Yin GZ, Li MH, Wang JG, Xu J, Li WP (2015) Mechanical behavior and permeability evolution of gas infiltrated coals during protective layer mining. Int J Rock Mech Min 80:292–301. Google Scholar
  54. Zhang R, Ai T, Li H, Zhang Z, Liu J (2013) 3D reconstruction method and connectivity rules of fracture networks generated under different mining layouts. Int J Min Sci Technol 23:863–871. CrossRefGoogle Scholar
  55. Zhang R, Ai T, Zhou HW, Ju Y, Zhang ZT (2015) Fractal and volume characteristics of 3D mining-induced fractures under typical mining layouts. Environ Earth Sci 73:6069–6080. CrossRefGoogle Scholar
  56. Zhang XG, Ranjith PG, Perera MSA, Ranathunga AS, Haque A (2016a) Gas transportation and enhanced coalbed methane recovery processes in deep coal seams: a review. Energy Fuel 30:8832–8849. CrossRefGoogle Scholar
  57. Zhang ZT, Zhang R, Xie HP, Gao MZ, Xie J (2016b) Mining-induced coal permeability change under different mining layouts. Rock Mech Rock Eng 49:3753–3768. CrossRefGoogle Scholar
  58. Zhou FB, Xia TQ, Wang XX, Zhang YF, Sun YN, Liu JS (2016) Recent developments in coal mine methane extraction and utilization in China: a review. J Nat Gas Sci Eng 31:437–458. CrossRefGoogle Scholar
  59. Zhou A, Wang K, Li L, Wang C (2017a) A roadway driving technique for preventing coal and gas outbursts in deep coal mines. Environ Earth Sci 76:236. CrossRefGoogle Scholar
  60. Zhou SD, Liu DM, Cai YD, Yao YB, Li ZT (2017b) 3D characterization and quantitative evaluation of pore-fracture networks of two Chinese coals using FIB–SEM tomography. Int J Coal Geol 174:41–54. CrossRefGoogle Scholar
  61. Zhu S, Wu SY, Cheng JW, Li SY, Li MM (2015) An underground air-route temperature prediction model for ultra-deep coal mines. Minerals-Basel 5:527–545. CrossRefGoogle Scholar

Copyright information

© Springer-Verlag GmbH Austria, part of Springer Nature 2018

Authors and Affiliations

  1. 1.State Key Laboratory of Coal Resources and Safe MiningChina University of Mining and Technology at BeijingBeijingChina
  2. 2.State Key Laboratory for Geomechanics and Deep Underground EngineeringChina University of Mining and Technology at XuzhouXuzhouChina
  3. 3.School of Mechanics and Civil EngineeringChina University of Mining and Technology at BeijingBeijingChina
  4. 4.Institute of Deep Earth Science and Green EnergyShenzhen UniversityShenzhenChina

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