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Multiple and Long-Term Disturbance of Gob-Side Entry Retaining by Grouped Roof Collapse and an Innovative Adaptive Technology

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Abstract

The demand for gob-side entry retaining (GSER) technology is extensive in Chinese coal mines because of its outstanding advantages. However, due to the occurrence of long-term roof movement disturbances, maintaining the conventional GSER over long distances is difficult. The urgent demand for this technology and its difficult maintenance are prominent contradictions faced in its application. In this paper, two characteristics of strata movement after mining that have great influence on GSER are determined in a physical simulation experiment. One is that the roof layers, which are dominated by the key strata (KS), collapse in multiple groups to form two-directional periodic pressures and superposed disturbances. The other is that the movement of the main roof will experience three stages of deformation, as follows: bending subsidence before collapse, sinking deformation at collapse and compressive deformation after collapse. In particular, the gradual compression of the bulging gangue in the gob extends the disturbance cycle. Therefore, it is difficult to maintain the GSER over long distances because of the long-term and multiple breaking disturbances of the roof layers. Mechanical models of KS breaking and GSER are established, and a method to determine the timing and strength of KS disturbances are proposed. Making use of the characteristics of staged collapse and fluctuating weighting of the overlying strata, an innovative technology named short-staged GSER is proposed. This technology maintains the maximum length of GSER within the optimal length, which ensures that the entry avoids superposed disturbances, and reduces the maintenance difficulty. The method for determining the key technical parameters is discussed, and an engineering case in panel 24202 of the Shaqu Mine in China is presented. From a back-calculation of measurements, the engineering practice demonstrates that the surrounding rock mass is stable, and the deformed entry size is safe when the length of the short-staged GSER does not exceed 100 m.

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Abbreviations

a :

The width of the GSER

b :

The width of the filling wall

E :

The equivalent elastic modulus after mining injury of the coal seam

E 0 :

The equivalent elastic modulus after mining injury of the immediate floor

E 1 :

The elastic modulus of the first layer

E 2 :

The equivalent elastic modulus after mining injury of the immediate roof

\({E_i}\) :

The elastic modulus of the i-layer

h 1 :

The height of the first layer

\({h_i}\) :

The height of the i-layer

h 0 :

The thicknesses of the immediate floor

h :

The thicknesses of the coal seam

h 2 :

The thicknesses of the immediate roof

H 0 :

The vertical distance between the KS and the coal seam

h k :

The thickness of the KS

K :

The residual bulking coefficient of the immediate roof

L k :

The length of the KS when it breaks

L m :

The mining distance when the KS breaks

L :

The length of the sloping block of the main roof

q :

The load on the KS

\({\left( {{q_n}} \right)_{\text{1}}}\) :

The load formed by the n-layers on the first layer

s′:

The deformation of the outside of the filling wall

s p :

The deformation of the main roof prior to collapse

s c :

The deformation of the main roof at collapse

s a :

The deformation of the main roof after collapse

s :

The total deformation of the main roof

x 0 :

The horizontal distance from the breaking point of the main roof to the entry

α :

The caving angle of the roof

δ :

The space height from the filling wall to the immediate roof

σ t :

The tensile strength of the KS

σ b :

The largest load in the filling wall

\({\gamma _i}\) :

The volume force of the i-layer

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Acknowledgements

This study was funded by the National Natural Science Foundation of China (Grant no. 51404251), the Natural Science Foundation of Jiangsu Province (Grant no. BK20140198), and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

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Authors and Affiliations

  1. School of Mines, Key Laboratory of Deep Coal Resource Mining, Ministry of Education, China University of Mining and Technology, No. 1 Daxue Road, Xuzhou, 221116, Jiangsu, China

    Changliang Han, Nong Zhang, Jiaguang Kan & Yiming Zhao

  2. State Key Laboratory of Deep Coal Mining and Environment Protection, Huainan, 232001, Anhui, China

    Junhua Xue

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  1. Changliang Han
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  2. Nong Zhang
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  3. Junhua Xue
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  4. Jiaguang Kan
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  5. Yiming Zhao
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Correspondence to Changliang Han or Nong Zhang.

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Han, C., Zhang, N., Xue, J. et al. Multiple and Long-Term Disturbance of Gob-Side Entry Retaining by Grouped Roof Collapse and an Innovative Adaptive Technology. Rock Mech Rock Eng 52, 2761–2773 (2019). https://doi.org/10.1007/s00603-018-1612-0

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