Effect of Premining on Hard Roof Distress Behavior: A Case Study

  • Weidong PanEmail author
  • Xiaodong Nie
  • Xinyuan Li
Original Paper


Considering the complex geological conditions of mining in the fully mechanized 828 working face of the Qingdong Coal Mine, a mining plan was developed for premining the upper No. 7 coal seam to control the hard roof and gas of the No. 8 coal seam. Failure depth of the No. 7 coal seam floor and the caving interval of the hard roof were analyzed using a proposed model based on the Terzaghi’s principle and rock beam theory, respectively. The movement rules of the overlying strata under premining (No. 7 coal seam) and non-premining conditions were analyzed using physical material similarity simulations experiment. Furthermore, field monitoring was performed to determine the working resistance of the hydraulic supports. The estimated results from the proposed method showed that the failure depth of the floor of the 726 working face was 13.8 m, which is in agreement with that noted during the field observation. The caving interval of the hard roof decreased from 24.9 m to 10.6 m after premining the No. 7 coal seam. In the simulation, the caving interval of the hard roof of the No. 8 coal seam decreased from 20 m to 10 m after premining the No. 7 coal seam. The hydraulic supports were effective in the actual production process, and the initial and periodic weighting intervals were 20.4 m and 10.4 m, respectively. These findings demonstrate that after premining the No. 7 coal seam, the initial and periodic weighting intervals decreased, thereby reducing the pressure intensity of the roof. This method effectively weakens the hard roof of the No. 8 coal seam. The issues pertaining to the hard roof during the mining of the 828 working face could be overcome by premining a protective coal seam of the upper No. 7 coal seam.


Hard roof Extremely thick coal seam Fully mechanized top-coal caving Physical material similarity simulation 

List of Symbols


Failure depth


Waist length of the isosceles triangle


Angle between the waist line and the helical radius


Inner-friction angle


Distance between the peak of abutment pressure and the working face


Maximum positive bending moment


Maximum negative bending moment


Distance between the center of the hanging main roof and the coal rib


Distance from the coal rib to the breaking position


Uniaxial tensile strength


Stiffness of the elastic support


Main roof deflection


Geometrical similarity ratio


Weighting interval


Motion similarity ratio


Density similarity ratio


Inertia moment


Distance from the coal rib to the breaking position when the roof is broken deep in the coal rib


Distance between logarithmic spiral and original point



The authors gratefully acknowledge the financial support from the National Key Research and Development Plan (No. 2018YFC0604501) and the Yue Qi Distinguished Scholar Project, China University of Mining & Technology, Beijing (No. 800015Z1138).


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Copyright information

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

Authors and Affiliations

  1. 1.State Key Laboratory of Coal Resources and Safe MiningChina University of Mining and TechnologyBeijingChina
  2. 2.Key Laboratory for Precise Mining of Intergrown Energy and ResourcesUniversity of Mining and TechnologyBeijingChina
  3. 3.Coal Industry Engineering Research Center of Top-coal Caving MiningBeijingChina

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