2. Gangue Backfilling Test in Datai Coal Mine
2.1. Project Introduction
2.2. Backfilling Technology and System Layout
2.3. Problems in Backfilling Practice
3. Numerical Modelling of Backfilling
3.1. Model Development and Simulation Method
3.2. Gangue Backfilling Process
3.2.1. Gangue Landslide Stage
3.2.2. Gangue Small-Scale Subsidence Stage
3.2.3. Funnel-Shaped Subsidence Stage
3.2.4. Large-Scale Subsidence Stage
3.3. Gangue Moving Area
- Gangue motionless area: Located in the upside of the coal-running slope, with a moving boundary line that exhibited a sector shape.
- Gangue landslide area: Because the gangue above the working face slides towards the coal-running slope, the gangue in the shallow part of the goaf exhibited a larger slide displacement.
- Gangue subsidence area: Located between the motionless area of the gangue and the working face. Gangue in this area subsides slowly.
- Gangue funnel-shaped subsidence area: Located in the connected space of the two-strip goaf, in which the gangue mainly backfilled the No. 2 strip goaf, and the movement was similar to a funnel.
- Gangue to-be-backfilled area: The subsidence pit formed in the shallow part of the goaf at the backfilling roadway was the effective backfilling area of the gangue in the next backfilling operation.
3.4. Gangue Moving Time
3.4.1. Variation of Gangue Moving Time with the Inclined Length of the Working Face
- When the inclined length of the working face was shorter than 67.5 m, the moving time was relatively short, no more than 40 min, and the time increment between mining stages fluctuated. This stage corresponded to the landslide stage, in which the gangue content inside the goaf was lower, and the movement velocity of the gangue after mining was fast.
- When the inclined length of the working face was longer than 67.5 m, the time increment between mining stages increased, and the gangue moving time increased rapidly. This stage corresponded to the small-scale subsidence stage, in which the goaf was completely full of gangue, and more time was needed for gangue backfilling.
3.4.2. Gangue Moving Time at Various Locations of the Working Face
- The inclined length of the working face should be shorter than a specific value to maintain a high backfilling ratio.
- When mining geological anomaly areas, especially faults, some measures should be taken in advance to reduce the influence on backfilling operation.
Conflicts of Interest
- Yao, Q.; Feng, T.; Liao, Z. Damage characteristics and movement of inclined strata with sublevel filling along the strike in the steep seam. J. China Coal Soc. 2017, 42, 3096–3105. (In Chinese) [Google Scholar] [CrossRef]
- Zhang, B.; Cao, S.G. Study on first caving fracture mechanism of overlying roof rock in steep thick coal seam. Int. J. Min. Sci. Technol. 2015, 25, 133–138. [Google Scholar] [CrossRef]
- Guo, W.Y.; Zhao, T.B.; Tan, Y.L.; Yu, F.H.; Hu, S.C.; Yang, F.Q. Progressive mitigation method of rock bursts under complicated geological condition. Int. J. Rock Mech. Min. Sci. 2017, 96, 11–22. [Google Scholar] [CrossRef]
- Huang, W.P.; Yuan, Q.; Tan, Y.L.; Wang, J.; Liu, G.L.; Qu, G.L.; Li, C. An innovative support technology employing a concrete-filled steel tubular structure for a 1000-m-deep roadway in a high in situ stress field. Tunn. Undergr. Space Technol. 2018, 73, 26–36. [Google Scholar] [CrossRef]
- Zhang, G.C.; Liang, S.J.; Tan, Y.L.; Xie, F.X.; Chen, S.J.; Jia, H.G. Numerical modeling for longwall pillar design: A case study from a typical longwall panel in China. J. Geophys. Eng. 2018, 15, 121–134. [Google Scholar] [CrossRef]
- Zhao, T.B.; Guo, W.Y.; Tan, Y.L.; Lu, C.P.; Wang, C.W. Case histories of rock bursts under complicated geological conditions. Bull. Eng. Geol. Environ. 2017, 77, 1529–1545. [Google Scholar] [CrossRef]
- Zhao, T.B.; Guo, W.Y.; Tan, Y.L.; Yin, Y.C.; Cai, L.S.; Pan, J.F. Case studies of rock bursts under complicated geological conditions during multi-seam mining at a depth of 800 m. Rock Mech. Rock Eng. 2018, 51, 1539–1564. [Google Scholar] [CrossRef]
- Wang, Y.; Taheri, A.; Xu, X. Application of Coal Mine Roof Rating (CMRR) in Chinese coal mines. Int. J. Min. Sci. Technol. 2018, 28, 491–497. [Google Scholar] [CrossRef]
- Ning, J.G.; Wang, J.; Bu, T.T.; Hu, S.C.; Liu, X.S. An innovative support structure for gob-side entry retention in steep coal seam mining. Minerals 2017, 7, 75. [Google Scholar] [CrossRef]
- Zhang, J.W.; Wang, J.C.; Wei, W.J.; Chen, Y.; Song, Z.Y. Experimental and numerical investigation on coal drawing from thick steep seam with longwall top coal caving mining. Arab. J. Geosci. 2018, 11, 1–9. [Google Scholar] [CrossRef]
- Yuan, Y.; Tu, S.H.; Wang, F.T.; Zhang, X.G.; Li, B. Hydraulic support instability mechanism and its control in a fully-mechanized steep coal seam working face with large mining height. J. South. Afr. Inst. Min. Metall. 2015, 115, 441–447. [Google Scholar] [CrossRef]
- Tan, Y.L.; Yu, F.H.; Ning, J.G.; Zhao, T.B. Design and construction of entry retaining wall along a gob side under hard roof stratum. Int. J. Rock Mech. Min. Sci. 2015, 77, 115–121. [Google Scholar] [CrossRef]
- Tan, Y.L.; Liu, X.S.; Ning, J.G.; Lu, Y.W. In situ investigations on failure evolution of overlying strata induced by mining multiple coal seams. Geotech. Test. J. 2017, 40, 244–257. [Google Scholar] [CrossRef]
- Zhou, Z.L.; Chen, L.; Cai, X.; Shen, B.T.; Zhou, J.; Du, K. Experimental investigation of the progressive failure of multiple pillar-roof system. Rock Mech. Rock Eng. 2018, 51, 1629–1636. [Google Scholar] [CrossRef]
- Lai, X.P.; Cai, M.F.; Ren, F.H.; Shan, P.F.; Cui, F.; Cao, J.T. Study on dynamic disaster in steeply deep rock mass condition in Urumchi Coalfield. Shock Vib. 2015. [Google Scholar] [CrossRef]
- Liu, X.S.; Tan, Y.L.; Ning, J.G.; Lu, Y.W.; Gu, Q.H. Mechanical properties and damage constitutive model of coal in coal-rock combined body. Int. J. Rock Mech. Min. Sci. 2018, 110, 140–150. [Google Scholar] [CrossRef]
- Tu, H.S.; Tu, S.H.; Zhang, C.; Zhang, L.; Zhang, X.G. Characteristics of the roof behaviors and mine pressure manifestations during the mining of steep coal seam. Arch. Min. Sci. 2017, 62, 871–891. [Google Scholar] [CrossRef]
- Gong, P.; Ma, Z.G.; Ni, X.Y.; Zhang, R.R. Floor heave mechanism of gob-side entry retaining with fully-Mechanized backfilling mining. Energies 2017, 10, 2085. [Google Scholar] [CrossRef]
- Gong, P.; Ma, Z.G.; Zhang, R.R.; Ni, X.Y.; Liu, F.; Huang, Z.M. Surrounding rock deformation mechanism and control technology for gob-Side entry retaining with fully mechanized gangue backfilling mining: A Case Study. Shock Vib. 2017. [Google Scholar] [CrossRef]
- Huang, P.; Spearing, A.J.S.; Feng, J.; Jessu, K.V.; Guo, S. Effects of solid backfilling on overburden strata movement in shallow depth longwall coal mines in West China. J. Geophys. Eng. 2018, 15, 2194–2208. [Google Scholar] [CrossRef]
- Zhang, J.X.; Deng, X.J.; Zhao, X.; Ju, F.; Li, B.Y. Effective control and performance measurement of solid waste backfill in coal mining. Int. J. Min. Reclam. Environ. 2017, 31, 91–104. [Google Scholar] [CrossRef]
- Zhang, J.X.; Li, M.; Taheri, A.; Zhang, W.Q.; Wu, Z.Y.; Song, W.J. Properties and application of backfill materials in coal mines in China. Minerals 2019, 9, 53. [Google Scholar] [CrossRef]
- Zhou, N.; Zhang, J.X.; Yan, H.; Li, M. Deformation behavior of hard roofs in solid backfill coal mining using physical models. Energies 2017, 10, 557. [Google Scholar] [CrossRef]
- Deng, X.J.; Klein, B.; Hallbom, D.J.; de Wit, B.; Zhang, J.X. Influence of particle size on the basic and time-dependent rheological behaviors of cemented paste backfill. J. Mater. Eng. Perform. 2018, 27, 3478–3487. [Google Scholar] [CrossRef]
- Deng, X.J.; Zhang, J.X.; Zhou, N.; de Wit, B.; Wang, C.T. Upward slicing longwall-roadway cemented backfilling technology for mining an extra-thick coal seam located aquifers: A case study. Environ. Earth Sci. 2017, 76, 789. [Google Scholar] [CrossRef]
- Feng, X.J.; Zhang, Q.M. The effect of backfilling materials on the deformation of coal and rock strata containing multiple goaf: A numerical study. Minerals 2018, 8, 224. [Google Scholar] [CrossRef]
- Wu, J.Y.; Feng, M.M.; Xu, J.M.; Qiu, P.T.; Wang, Y.M.; Han, G.S. Particle size distribution of cemented rockfill effects on strata stability in filling mining. Minerals 2018, 8, 407. [Google Scholar] [CrossRef]
- Zhang, X.G.; Lin, J.; Liu, J.X.; Li, F.; Pang, Z.Z. Investigation of hydraulic-mechanical properties of paste backfill containing coal gangue-fly ash and its application in an underground coal mine. Energies 2017, 10, 1309. [Google Scholar] [CrossRef]
- Taheri, A.; Tatsuoka, F. Stress-strain relations of cement-mixed gravelly soil from multiple-step triaxial compression test results. Soils Found. 2012, 52, 748–766. [Google Scholar] [CrossRef]
- Taheri, A.; Tatsuoka, F. Small- and large-strain behaviour of a cement-treated soil during various loading histories and testing conditions. Acta Geotech. 2015, 10, 131–155. [Google Scholar] [CrossRef]
- Zhao, Y.; Soltani, A.; Taheri, A.; Karakus, M.; Deng, A. Application of slag-cement and fly ash for strength development in cemented paste backfills. Minerals 2019, 9, 22. [Google Scholar] [CrossRef]
- Li, J.M.; Huang, Y.L.; Chen, Z.W.; Li, M.; Qiao, M.; Kizil, M. Particle-crushing characteristics and acoustic-emission patterns of crushing gangue backfilling material under cyclic loading. Minerals 2018, 8, 244. [Google Scholar] [CrossRef]
- Li, J.M.; Huang, Y.L.; Qi, W.Y.; Kong, G.Q.; Song, T.Q. Loose gangues backfill body‘s acoustic emissions rules during compaction test: based on solid backfill mining. CMES Comp. Model Eng. 2018, 15, 85–103. [Google Scholar] [CrossRef]
- Li, B.; Ju, F. An experimental investigation into the compaction characteristic of granulated gangue backfilling materials modified with binders. Environ. Earth Sci. 2018, 77, 284. [Google Scholar] [CrossRef]
- Zhao, T.B.; Zhang, Z.Y.; Yin, Y.C.; Tan, Y.L.; Liu, X.Q. Ground control in mining steeply dipping coal seams by backfilling with waste rock. J. South. Afr. Inst. Min. Metall. 2018, 118, 15–26. [Google Scholar] [CrossRef]
- Al-Halbouni, D.; Holohan, E.P.; Taheri, A.; Schöpfer, M.P.J.; Emam, S.; Dahm, T. Geomechanical modelling of sinkhole development using Distinct Elements: Model verification for a single void space and application to the Dead Sea area. Solid Earth 2018, 9, 1341–1373. [Google Scholar] [CrossRef]
- Wang, C.; Deng, A.; Taheri, A. Three-dimensional discrete element modeling of direct shear test for granular rubber-sand. Comput. Geotech. 2018, 97, 204–216. [Google Scholar] [CrossRef]
- Potyondy, D.; Cundall, P. A bonded-particle model for rock. Int. J. Rock Mech. Min. Sci. 2004, 41, 1329–1364. [Google Scholar] [CrossRef]
- Yin, Y.C.; Zou, J.C.; Zhang, Y.B.; Qiu, Y.; Fang, K.; Huang, D.M. Experimental study of the movement of backfilling gangues for goaf in steeply inclined coal seams. Arab. J. Geosci. 2018, 11, 318. [Google Scholar] [CrossRef]
|Stratum||Rocks||Average Thickness (m)||Character Description|
|Main roof||Siltstone||14.7||Gray black, silicon cementation.|
|Immediate roof||Siltstone||4.1||Gray black, silicon cementation.|
|Coal seam||No. 5 coal||1.7||Black, half bright type.|
|Immediate floor||Siltstone||7.7||Gray black, silicon cementation.|
|Main floor||Siltstone||20||Gray black, silicon cementation.|
|Parameter||Rock Stratum||Coal Seam||Gangue|
|Density ρ (kg/m3)||2500||1400||2500|
|Radius r (m)||0.4–0.6||0.4–0.6||0.4–0.6|
|Normal contact stiffness kn (GPa)||5||1||5|
|Shear contact stiffness ks (GPa)||2||0.5||2|
|Friction coefficient f||0.5||0.5||0.5|
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