This research is aimed at investigating the influence of the coal height ratio on the mechanical properties and damage behavior of rock-coal-rock combined samples (RCRCS) under coupled static and dynamic loads. For this purpose, a uniaxial cyclic dynamic loading experiment with four different coal height ratios of RCRCS was conducted. Mechanical properties, failure modes, and wave velocity evolution of RCRCS were analyzed; the process of rock burst under coupled static and dynamic loads in rock-coal-rock combined structure was discussed. The following research results are obtained. (1) The peak strength of RCRCS under static and dynamic load decreases with the increasing coal height ratio as an inverse proportional function. (2) The loading and unloading modulus remains consistent for the same levels of dynamic load; the coal height ratio of 40% may be the limit for the stable value of modulus. (3) The increase of the coal height in RCRCS leads to a gradual increase of the energy release rate; the cracks develop preferentially in coal and then extend to rock sample. The distribution of AE events and damage is consistent with the distribution of passive wave velocity. The research results provide important scientific bases for the guidance of early warning of rock burst.

Upper protective layer (UPL) mining is extensively utilised as a pressure relief strategy to prevent outbursts and coal bursts. However, when the excavation height of the protected layer is substantial, the depressurisation efficacy of the protective layer may be diminished. This paper takes the Haishiwan coal mine in China as a case study and explores the stress evolution and influencing factors in the mining of extra-thick coal seam beneath the protective layer through theoretical analysis, numerical simulation, and field observation. The results indicate that increasing the excavation height of the coal seam will lead to the upward development of the collapse zone in the overburden of the goaf, with the “masonry beam” structure formed at a higher position by key strata blocks. The overburden above the masonry beam will be supported by the coal rock masse on both sides of the structure, leading to increased stress on the coal seam near the goaf and eliminating the depressurisation effect of the protective layer. Numerical simulation shows that factors such as faults, protective layers, interlayer spacing, and the height of coal seam excavation significantly affect the stress distribution in the protected layer. With the increase in interlayer spacing and the thickness of coal seam extraction, the stress reduction phenomenon of the UPL gradually decreases, especially with an abnormal stress concentration of the gob-side coal seam. Observations of Surface subsidence and the distribution of mining-induced seismic events corroborate the conclusions of theoretical analysis and numerical simulations. The results offer valuable guidance for the mining of extra-thick coal seams and the selection of the UPL.

Coal bursts occurring in steeply inclined coal seams (SICSs) are increasingly severe. To solve this problem, a mechanical model for the distribution of static stress on coal‐rock masses along panels and the distribution of dynamic load induced by the breakage of thick and hard roofs with propagation distance was established. The stress characteristics after a superposition of dynamic and static loads on the roof and floor roadways (R_r and R_f) were determined. In addition, precursory information characteristics and index sensitivities of four indices for dynamic loads and the CT index for static loads based on seismic tomography were separately analyzed. The monitoring and warning indices for SICSs and flat seams were compared. The results showed that the static stress of R_r was significantly higher than that of R_f, which provided a basis for the stress‐triggering coal burst behaviors. Three indices for dynamic loads and seismic tomography results exhibited remarkable precursory information and high sensitivity. However, the performance of lack of shock index is poor. The continuous anomaly and the contradiction of indices at R_r and R_f can be considered as precursory information for predicting coal bursts.

Microseismic monitoring systems (MMS) have become increasingly crucial in detecting tremors in coal mining. Microseismic sensors (MS), integral components of MMS, profoundly influence positioning accuracy and energy calculations. Hence, calibrating these sensors holds immense importance. To bridge the research gap in MS calibration, this study conducted a systematic investigation. The main conclusions are as follows: based on calibration tests on 102 old MS using the CS18VLF vibration table, it became evident that certain long-used MS in coal mines exhibited significant deviations in frequency and amplitude measurements, indicating sensor failure. Three important calibration indexes, frequency deviation, amplitude deviation, and amplitude linearity are proposed to assess the performance of MS. By comparing the index of old and new MS, critical threshold values were established to evaluate sensor effectiveness. A well-functioning MS exhibits an absolute frequency deviation below 5%, an absolute amplitude deviation within 55%, and amplitude linearity surpassing 0.95. In normal operations, the frequency deviation of MS is significantly smaller than the amplitude deviation. Simplified waveform analysis has unveiled a linear connection between amplitude deviation and localization results. An analysis of the Gutenberg–Richter microseismic energy calculation formula found that the microseismic energy calculation is influenced by both the localization result and amplitude deviation, making it challenging to pinpoint the exact impact of amplitude deviation on microseismic energy. Reliable MS, as well as a robust MS, serve as the fundamental cornerstone for acquiring dependable microseismic data and are essential prerequisites for subsequent microseismic data mining. The insights and findings presented here provide valuable guidance for future MS calibration endeavors and ultimately can guarantee the dependability of microseismic data.

The true triaxial test can accurately simulate the dynamic and static load superposition environment of deep mining and then reproduce the spatial and temporal evolution process of coal-rock dynamic disasters. This study used a self-developed true triaxial coal-rock dynamic behavior test system to investigate the dynamic failure characteristics and mechanism of coal bursts under different mining-induced stress disturbances. The results show that the perturbation duration of the coal samples under quasi-static load decreases with the increase of the disturbance rate, and the perturbation stress level increases first and then decreases. The coal samples can accumulate higher strain energy and show progressive and dynamic failure. The perturbation duration and stress peak of the coal sample under the cycle load decreased with the increase of the cycle amplitude and frequency, and the coal sample first spalled off on the free surface. The damage then developed internally until the coal burst. The perturbation duration and stress peak of coal samples decrease with the increase of transient stress and the perturbation stress levels. The dynamic failure process of coal samples is straightforward, and the strength of coal burst is violent and is more difficult to predict. The conclusions obtained help to deepen the understanding of the triggering mechanism of coal bursts.