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

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Abstract

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.

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Abbreviations

H:

Failure depth

r 0 :

Waist length of the isosceles triangle

α:

Angle between the waist line and the helical radius

φ:

Inner-friction angle

L :

Distance between the peak of abutment pressure and the working face

M 1 :

Maximum positive bending moment

M 2 :

Maximum negative bending moment

l :

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

X :

Distance from the coal rib to the breaking position

R T :

Uniaxial tensile strength

K :

Stiffness of the elastic support

Y :

Main roof deflection

αL :

Geometrical similarity ratio

L 1T :

Weighting interval

α T :

Motion similarity ratio

α γ :

Density similarity ratio

I:

Inertia moment

x2 :

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

r :

Distance between logarithmic spiral and original point

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Acknowledgements

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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Authors and Affiliations

  1. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing, 100083, China

    Weidong Pan, Xiaodong Nie & Xinyuan Li

  2. Key Laboratory for Precise Mining of Intergrown Energy and Resources, University of Mining and Technology, Beijing, 100083, China

    Weidong Pan, Xiaodong Nie & Xinyuan Li

  3. Coal Industry Engineering Research Center of Top-coal Caving Mining, Beijing, 100083, China

    Weidong Pan, Xiaodong Nie & Xinyuan Li

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  1. Weidong Pan
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  2. Xiaodong Nie
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Correspondence to Weidong Pan.

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Pan, W., Nie, X. & Li, X. Effect of Premining on Hard Roof Distress Behavior: A Case Study. Rock Mech Rock Eng 52, 1871–1885 (2019). https://doi.org/10.1007/s00603-018-1657-0

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