Paper contribution

Unloading impact failure mechanisms and kinetic energy analysis of coal-rock composites in deep roadways

Dejian LI; Bo Hu; Tongjie Sun; Mingyuan Zhang

Proceedings
EUROCK 2026
Pages
859-864
Submitted
28 January 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

Dynamic hazards induced by stress unloading during deep roadway excavation in coal–rock composite strata threaten the stability of underground engineering. To clarify the unloading impact failure mechanisms of coal-rock composites and quantify the failure intensity, loading and unloading experiments were conducted on specimens with five different coal-rock ratios (1:0, 2:1, 1:1, 1:2, 0:1) using a true-triaxial experimental system to simulate roadway excavation. The peak failure stress (σp), acoustic emission (AE) characteristics, failure patterns, fragment characteristics and kinetic energy were analyzed. The results show that the σpincreased with increasing rock content. Composite specimens generally exhibited lower cumulative AE counts and energy than single lithology specimens. Microparticulate fragments were observed only in the specimen with a coal-rock ratio of 1:1. Coal-rock composites exhibited progressive failure behavior, including precursory small-scale grains ejection and multiple impacts. Since the total kinetic energy of ejected fragments may overestimate unloading impact failure intensity due to the tendency of coal to break down into abundant fine fragments, a new parameter, the unit volume kinetic energy (Eu), was proposed to address this limitation. The Eu values of composite specimens (2:1, 2.58 J/cm³; 1:1, 2.54 J/cm³; 1:2, 3.76 J/cm³) were higher than those of coal (1:0, 0.99 J/cm³) and sandstone (0:1, 0.84 J/cm³) specimens. A strong correlation between Eu and bursting-pit volume confirmed the reliability of Eu as a metric for unloading impact failure kinetic energy. These findings clarify the failure mechanisms and provide a crucial practical metric for quantitatively assessing dynamic failure intensity in deep roadways.

Contributors

Authors

  1. Dejian LI State Key Laboratory of Tunnel Engineering, China University of Mining and Technology, Beijing, 100083, China; School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing, 100083, China
  2. Bo Hu State Key Laboratory of Tunnel Engineering, China University of Mining and Technology, Beijing, 100083, China; School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing, 100083, China
  3. Tongjie Sun State Key Laboratory of Tunnel Engineering, China University of Mining and Technology, Beijing, 100083, China; School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing, 100083, China
  4. Mingyuan Zhang State Key Laboratory of Tunnel Engineering, China University of Mining and Technology, Beijing, 100083, China; School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing, 100083, China

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References

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