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<p>To elucidate the mechanical response and damage evolution mechanisms of coal‒rock assemblies in deep high-temperature environments, a combined approach utilizing a comprehensive testing platform for determining the cryomechanical properties and freeze-damage characteristics of gas-bearing coal‒rock assemblies (equipped with a high-temperature loading and mechanical testing module), along with discrete element numerical simulation, was employed. Dynamic impact tests were conducted on both individual coal–rock units and coal–rock assemblies under thermomechanical coupling at temperatures ranging from 30 to 90&#xa0;°C, and the ZWT viscoelastic model was improved by coupling it with the Weibull damage model introducing a temperature effect correction process. The results indicate that the dynamic stress‒strain curves of the samples under thermomechanical coupling can be divided into four stages: compaction, elastic, crack propagation, and softening failure. Thermal damage presents a three-stage evolution pattern: rapid damage (30–50&#xa0;°C), slow-change phase (50–70&#xa0;°C), sustained damage (70–90&#xa0;°C), and 70&#xa0;°C serves as the critical threshold at which an abrupt change in the mechanical properties of coal–rock assemblies occurs. At this temperature, elastic modulus sharply decreases by 54.41%. However, it rebounds significantly at 90&#xa0;°C owing to preliminary coal pyrolysis recementation and siltstone skeleton hardening, whereas the peak strength shows a non-monotonic variation characteristic. The failure mode of the samples is dominated by tensile cracks, and thermal damage is highly concentrated in highly thermally stress-sensitive siltstone layers rather than in traditionally assumed weak coal bodies, which verifies the presence of a new sandstone-dominated thermal damage mode. The improved dynamic constitutive model based on ZWT describes the stress‒strain relationship well after the samples experienced impact at high temperatures but is unable to satisfactorily characterize the compaction stage. Acoustic emission and force chain evolution results further confirm that elevated temperatures cause cement bond failure, reduced contact force chains, and interface weakening, which promote localized deformation and cause macrostructural instability to accelerate. Conclusions indicate that 70&#xa0;°C represents a critical threshold at which abrupt changes in coal‒rock composite mechanical properties occur. Thus, integrated temperature monitoring and support design are needed in deep high-temperature engineering. This study reveals the nonlinear characteristics of thermomechanical coupled failure modes and mechanical responses, providing a theoretical foundation and a practical guidance for ensuring safe deep mining operations and developing early warning systems for disaster avoidance.</p>

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Mechanical Properties of Deep Coal‒Rock Complexes Under Thermal‒Mechanical Coupling

  • 期刊论文

  • 发表日期：

    2026年7月24日

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  • Liu Jun,
  • Wu Wenming,
  • Chen Hanbing,
  • Chen Xiangjun,
  • Ma Shujun

摘要

To elucidate the mechanical response and damage evolution mechanisms of coal‒rock assemblies in deep high-temperature environments, a combined approach utilizing a comprehensive testing platform for determining the cryomechanical properties and freeze-damage characteristics of gas-bearing coal‒rock assemblies (equipped with a high-temperature loading and mechanical testing module), along with discrete element numerical simulation, was employed. Dynamic impact tests were conducted on both individual coal–rock units and coal–rock assemblies under thermomechanical coupling at temperatures ranging from 30 to 90 °C, and the ZWT viscoelastic model was improved by coupling it with the Weibull damage model introducing a temperature effect correction process. The results indicate that the dynamic stress‒strain curves of the samples under thermomechanical coupling can be divided into four stages: compaction, elastic, crack propagation, and softening failure. Thermal damage presents a three-stage evolution pattern: rapid damage (30–50 °C), slow-change phase (50–70 °C), sustained damage (70–90 °C), and 70 °C serves as the critical threshold at which an abrupt change in the mechanical properties of coal–rock assemblies occurs. At this temperature, elastic modulus sharply decreases by 54.41%. However, it rebounds significantly at 90 °C owing to preliminary coal pyrolysis recementation and siltstone skeleton hardening, whereas the peak strength shows a non-monotonic variation characteristic. The failure mode of the samples is dominated by tensile cracks, and thermal damage is highly concentrated in highly thermally stress-sensitive siltstone layers rather than in traditionally assumed weak coal bodies, which verifies the presence of a new sandstone-dominated thermal damage mode. The improved dynamic constitutive model based on ZWT describes the stress‒strain relationship well after the samples experienced impact at high temperatures but is unable to satisfactorily characterize the compaction stage. Acoustic emission and force chain evolution results further confirm that elevated temperatures cause cement bond failure, reduced contact force chains, and interface weakening, which promote localized deformation and cause macrostructural instability to accelerate. Conclusions indicate that 70 °C represents a critical threshold at which abrupt changes in coal‒rock composite mechanical properties occur. Thus, integrated temperature monitoring and support design are needed in deep high-temperature engineering. This study reveals the nonlinear characteristics of thermomechanical coupled failure modes and mechanical responses, providing a theoretical foundation and a practical guidance for ensuring safe deep mining operations and developing early warning systems for disaster avoidance.