Long-term evolution of overlying rock fractures in mined-out areas and its effect on gas flow conductivity

During the operation of artificial underground structures, the surrounding rock experiences fatigue and creep damage caused by several types of disturbances under long-term constant loading. To quantify the mechanical response of sandstone under creep–fatigue loading, a damage–hardening evolution model based on the linear superposition concept is proposed. In the model, coupling is applied to represent the synergistic effect of creep and fatigue. Creep–fatigue tests of sandstone specimens are conducted under multilevel loading. The damage and hardening effects of sandstone under creep–fatigue loading are complex. Hardening is the dominant effect under low creep–fatigue loads, and damage is the dominant effect under high creep–fatigue loads. The strength of the rock specimens undergoes increasing and decreasing trends under this loading path, and the evolution of the Mohr–Coulomb envelope is discussed. The proposed model can be used to describe the test data and the evolution of the creep–fatigue process. With increasing creep–fatigue number, the acoustic emission amplitude, energy, and cumulative counts increase. However, the amplitude is more sensitive than the energy, indicating that it is more suitable for describing creep–fatigue loading. Furthermore, the peak frequencies of the AE signals are mostly distributed in the 0–15 kHz, 15–30 kHz, 30–45 kHz, and 45–55 kHz regions. The signal proportion in the 45–55 kHz zone decreases with the creep–fatigue number. However, other frequency zones increase with the creep–fatigue number. This phenomenon illustrates that the crack scale of the specimens increases with the creep–fatigue number.

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Characterization and differences of acoustic signals response of semi-circular red sandstone under combined monotonous and cyclic loadings

Zou,

Chen,

Chen

et al. 2024

Geomech. Geophys. Geo-energ. Geo-resour.

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After underground coal mining, rocks are often subjected to tensile damage by the interaction of dynamic and static loadings. The process of rock fracture development under dynamic and static loadings will be released in the form of acoustic energy to form an acoustic signal. In addition, the acoustic signals in dynamic loading differ from that in static loading. Therefore, this study conducted three-point bending experiments with continuous dynamic loading and dynamic–static coupling loading on semi-circular red sandstone specimens. The acoustic signals during red sandstone specimens’ tensile damage were monitored in real-time. The results show that red sandstone’s tensile strength and deformation are enhanced under dynamic–static coupling loading. The red sandstone has a more effective acoustic emission hit rate, energy rate, and r during tensile damage under continuous dynamic loading. In dynamic loading, macroscopic fractures are developed in red sandstone, which has few acoustic emission events but releases strong acoustic signals. In static loading, the pores inside the red sandstone are compacted, the rock particles are rearranged, and the tiny fractures are closed, and its acoustic emission events are many but low in energy. In addition, the rock particles in the front area of the static loading fracture are tightly cemented, which increases the difficulty of separating the rock particles in the front area of the fracture under dynamic loading. Then weakening the red sandstone fracture development process and suppressing its acoustic signals. The research results provide more insight into the differences in tensile damage processes in red sandstone under the interaction of dynamic and static loadings.

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Long-term evolution of overlying rock fractures in mined-out areas and its effect on gas flow conductivity

Cited by 11 publications

References 24 publications

Distribution Patterns of the Dominant Mining Fracture Fields in Pressure Relief Methane Migration

Distribution Patterns of the Dominant Mining Fracture Fields in Pressure Relief Methane Migration

Damage and hardening evolution characteristics of sandstone under multilevel creep–fatigue loading

Characterization and differences of acoustic signals response of semi-circular red sandstone under combined monotonous and cyclic loadings

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