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Stress Evolution in Roadway Rock Bolts During Mining in a Fully Mechanized Longwall Face, and an Evaluation of Rock Bolt Support Design

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Abstract

Rock bolts are widely used in coal mines throughout China. Approximately 8,000 km of roadways are excavated in coal mines every year in China, 80 % of which are supported by rock bolts. At present, the design of rock bolt support schemes is mainly based on analogies and experience from previous projects. In the present study, in order to evaluate the design of rock bolt support in roadways, several cross sections of a roadway were monitored for rock bolt stress during the roadway excavation and mining. The study results show that the stress in the rock bolts varied in the areas 20 m behind the excavating face and 30 m ahead of the mining face. For the rock bolts observed in this study, the max axial force was within the design limit of the bolts, thus the support design was shown to be acceptable. Then, numerical simulation was performed using FLAC3D to investigate the stress evolution in the rock bolts during the mining of the fully mechanized longwall face. The simulation results show an overall agreement with the in situ measurements. Finally, parametric study pertaining to length, anchorage length, and rock bolt spacing was carried out with the numerical model, and several suggestions for the support design were proposed.

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Abbreviations

P :

Support strength of hydraulic supports

k :

Ratio of thickness of roof stratum to that of coal seam

h :

Max mining height

γ :

Unit weight of rock mass in the roof

g :

Gravitational acceleration

c g :

Grout cohesive strength per unit length

D :

Diameter of rock bolt or cable

t :

Annulus thickness

τ peak :

Shear strength of grout/rock or reinforcing/grout interface

k g :

Grout stiffness per unit length

G :

Grout shear modulus

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Acknowledgments

The authors gratefully acknowledge the support from the Natural Science Foundation of China (grant no. 51104151 and 51227003), National Basic Research Program of China (973 Program, grant no. 2013CB227902), and Fundamental Research Funds for the Central Universities (grant no. 2011QNA18).

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Authors and Affiliations

  1. State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou, 221008, China

    Kai Zhang, Guimin Zhang, Rongbin Hou & Yu Wu

  2. ChengJiao Coal Mine, HeNan Coal and Chemical Company, Yongcheng, 476600, China

    Hongqi Zhou

Authors
  1. Kai Zhang
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  2. Guimin Zhang
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  3. Rongbin Hou
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  4. Yu Wu
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  5. Hongqi Zhou
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Correspondence to Guimin Zhang.

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Zhang, K., Zhang, G., Hou, R. et al. Stress Evolution in Roadway Rock Bolts During Mining in a Fully Mechanized Longwall Face, and an Evaluation of Rock Bolt Support Design. Rock Mech Rock Eng 48, 333–344 (2015). https://doi.org/10.1007/s00603-014-0546-4

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  • DOI: https://doi.org/10.1007/s00603-014-0546-4

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