Mechanical Behaviors and Equations of Composite Coal-Rock under True Triaxial Loading-Unloading at Varying Burial Depths

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发表日期：

2025年11月18日

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Xiaoliang Li,
Zhentang Liu,
Yubing Liu,
Quancong Zhang,
Li Zhang,
Weinan Wang,
Jianyang Yu,
Xianshang Zhang

摘要

During coal mining, coal seams and the surrounding roof and floor strata do not exist in isolation; instead, they form an integrated composite coal–rock system, which serves as the fundamental structural unit of the mining space. Understanding the mechanical behaviors and equations of composite coal–rock are critical for the prevention and control of rockbursts. This study conducted the true triaxial loading–unloading failure tests on composite coal–rock to investigate its mechanical properties and energy evolution. Furthermore, the true triaxial constitutive and anisotropic stress equations for composite coal–rock, considering the burial depth, were developed. The results show that the characteristic stress, strain flexibility, elastic energy, and dissipated energy of composite coal–rock all increase (decrease) with the increases of the unloading stress level factor λ (unloading speed ${V}_{3}$ $V_{3}$ ). The self-inhibition model can effectively describe the evolution process of the elastic energy in composite coal and rock. The greater λ ( ${V}_{3}$ $V_{3}$ ), the weaker (stronger) self-inhibition effect. The constitutive equation can characterize the deformation and strength of composite coal–rock under loading–unloading at different burial depths. The additional stress between the coal and rock in composite coal–rock is equal in magnitude but opposite in direction. The sum of the intermediate (minimum) effective stresses in the coal and rock equals twice the intermediate (minimum) principal stress of the composite coal–rock. The loading–unloading stress path can alter the magnitude and direction of anisotropic stress in both coal and rock, but it does not affect the stress relationship between them.