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Mechanism of core discing in the relaxation zone around an underground opening under high in situ stresses

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Abstract

Core discing is a brittle rock failure during borehole drilling in intact rock subjected to high in situ stresses. This failure mode has been recognized as an important index for assessing underground projects under high in situ stresses. With increasing depth of underground space exploitation, core discing occurs not only in highly-stressed intact rock, but also in the relaxation zone of the surrounding rock masses. In the latter case, the disc thickness is even smaller, and the mechanism is significantly different from that of core discing in highly-stressed intact rock. In this study, the correlation between the regional geological structures and the disc thickness in the relaxation zone is analyzed based on the deep auxiliary tunnel of the Jinping hydropower project. A “structural arch” model, applicable for analyzing the mechanical behaviors of fractures and rock blocks in the relaxation zone, is proposed. The model is then verified by laboratory similarity tests and numerical simulations. Finally, it is revealed that the “discontinuous” stress field in the relaxation zone is the main cause of core discing in the relaxation zone around underground openings subjected to high in situ stresses.

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Abbreviations

I p :

the geometric size of the prototype.

I m :

the geometric size of the model.

γ p :

the bulk density of the prototype.

γ m :

the bulk density of the model.

C l :

the similarity ratio of geometric size.

C γ :

the similarity ratio of bulk density.

C σc :

the similarity ratio of compressive strength.

C σt :

the similarity ratio of tensile strength.

C σ :

the similarity ratio of stress.

C E :

the similarity ratio of elastic modulus.

C C :

the similarity ratio of cohesion.

C ε :

the similarity ratio of strain.

C μ :

the similarity ratio of Poisson’s ratio.

C φ :

the similarity ratio of internal friction angle.

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Acknowledgments

This study was supported by the National Natural Science Foundation of China (Grant No. 51109035) and the Key Projects in the National Science & Technology Pillar Program during the Twelfth Five-Year Plan Period of China (Grant No. 2016YFC0801605).

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Authors and Affiliations

  1. Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang, Liaoning, 110819, China

    Long An, Changyu Jin, Dong Liu & Chenggong Ding

  2. School of Mining Engineering, Liaoning Shihua University, Fushun, Liaoning, 113001, China

    Xinghang Dai

Authors
  1. Long An
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  2. Changyu Jin
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  3. Dong Liu
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  4. Chenggong Ding
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  5. Xinghang Dai
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Correspondence to Dong Liu.

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An, L., Jin, C., Liu, D. et al. Mechanism of core discing in the relaxation zone around an underground opening under high in situ stresses. Bull Eng Geol Environ 77, 1179–1189 (2018). https://doi.org/10.1007/s10064-017-1168-3

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  • DOI: https://doi.org/10.1007/s10064-017-1168-3

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