To further understand the fracture behavior of rock materials containing en echelon flaws and determine precursor information for the final collapse of damaged mineral assemblies under compression, a series of uniaxial compression experiments using a loading system, an acoustic emission system and a video camera was conducted on sandstone specimens containing en echelon flaws. The mechanical properties, energy dissipation characteristics and acoustic emission parameters of compression failure of selected specimens were successively analyzed. The results showed that crack initiation was accompanied by a stress drop, step-like characteristics on the energy consumption curve and increased crackling noises, which were used as early warning signals before the final collapse happened. In addition, we used the histogram statistics method and maximum likelihood method to analyze the distribution of acoustic emission energy and determined that the acoustic emission energy distributions of sandstone specimens containing en echelon flaws followed a power law. With the progress of the experiment, the optimum exponents changed in different stages and gradually decreased as failure was approached, which could also be used as an early warning signal before the final collapse happened. This paper may provide some theoretical basis for monitoring and warning about the collapse and instability of engineering rock masses containing en echelon flaws.

The rockburst hazard is a primary geological disaster endangering the environment in underground engineering. Due to the complexity of the rockburst mechanism, traditional methods are insufficient to predict the rockburst hazard objectively, especially when dealing with an imbalanced dataset. To address this issue, the hybrid models of PSO-BPNN-AdaBoost and PSO-BPNN-XGBoost were developed to predict rockburst hazards in this study. First, a rockburst dataset with 266 cases was constructed, containing six indicators: the maximum tangential stress, uniaxial compressive strength, uniaxial tensile strength, elastic deformation energy index, tangential stress index, and brittleness coefficient of strength. Then, the original dataset was oversampled using the synthetic minority oversampling technique (SMOTE) for dataset balancing. Subsequently, the PSO-BPNN-AdaBoost and PSO-BPNN-XGBoost models were constructed and evaluated to have the best accuracies of 0.901 and 0.851, respectively. Finally, the developed models were applied to predict the rockburst hazard in the Daxaingling Tunnel, the Cangling Tunnel, and the Zhongnanshan Tunnel shaft. The results indicate that the obtained rockburst hazard levels are consistent with engineering records, and the developed PSO-BPNN-AdaBoost and PSO-BPNN-XGBoost models are reliable for rockburst prediction.

To further understand the anisotropic behavior of layered rock and the precursor characteristics of rock mass instability, a series of uniaxial compression experiments using a loading system and an acoustic emission system was conducted on sandstone specimens. The influence of bedding on the mechanical parameters and failure modes and the statistical evolution of the acoustic emission energy were successively discussed. The results of axial stress-strain curves and crack propagation modes showed that the existence of a bedding plane increased the anisotropy of the rocks, and the magnitude of the bedding inclination also exerted certain influence on this anisotropy. Furthermore, we used the least squares method and the maximum likelihood method to analyze the value and power-law exponent, respectively. The results of statistical evolution of acoustic emission energy showed that the value, the effective power-law exponent, and the optimal exponent could be used as monitoring indexes for the rock mass stability. With the progress of the experiment, the following phenomena pertaining to acoustic emission activities occurred, which may indicate imminent danger of collapse: (1) the crackling noises increased significantly; (2) the variation of the value exhibited a significant downward trend; and (3) the effective power-law exponent and the optimal exponent changed in different stages and gradually decreased as the final failure was approached. The findings in this paper may provide a theoretical basis for predicting the collapse and instability of rock mass structures.

With the improvement in tailing mining-grade requirements and in mineral processing technology, tailing materials tend to be fine-grained. Under the action of earthquakes, a tailing dam is prone to liquefaction, which endangers the safety and stability of the dam. To further explore the dynamic properties of tailing silt under cyclic stress, through a series of dynamic triaxial experiments, we investigated the growth of the hysteresis curve, the development of pore pressure, and the energy dissipation law of tailing silt. The experimental findings indicated that increasing the density of the sample significantly improves its liquefaction resistance and the pore pressure development curve can be fitted using the BiDoseResp function. At the same cyclic stress ratio, the sample’s anti-liquefaction strength did not rise monotonically with increasing confining pressure but changed variably at values near a specified low confining pressure; when the sample density rose under the same settings, the specific confining pressure reduced. We also further discussed the evolution law of the stress–strain curves of tailing silt. The results further explored the dynamic characteristics of tailing silt, which can provide some reference for the seismic design and reinforcement measures of many fine-grained tailing dams.

Developing green mining technology for medium-to low-grade mines requires achieving minimal or no damage to the mining area’s ecological environment. A medium-to low-grade phosphate mine in Hubei Province was taken as the research object in this study. The tailings were selected as the main filling aggregate. Indoor tests and theoretical analysis were conducted to analyze the influence of curing age, the water–cement ratio, the cement–sand ratio, and slurry concentration on the strength of the cemented backfill. Furthermore, a multi-factor non-linear mathematical model of the strength of the cementitious filler was established. The study results indicated that the strength of backfill increased linearly with the increase in the curing age, decreased negatively with the increase in the water–cement ratio, and increased exponentially with the increase in the cement–sand ratio and the slurry concentration. The multivariate non-linear prediction model of the strength of the filling body at different ages was also established based on the test results. This predictive model could effectively predict the strength of the cemented backfill, and the error value was not larger than 4%. Our research results can lay a theoretical foundation for developing medium-to low-grade phosphate mine filling with tailings as the main filling aggregate.

During coal mining, gas pressure co-evolves with in-situ stress and exhibits constant-amplitude cyclic loading-unloading (CACLU) characteristics. To elucidate the deformation and seepage response of coal masses under mining disturbances, this study performs triaxial seepage tests under constant-amplitude cyclic gas pressure loading-unloading. The results show that axial strain accumulates in the compressive direction with increasing cycles, while radial and volumetric strains follow distinct evolution patterns. Under low gas pressure, radial strain transitions from dilation to compression, and volumetric strain grows compressively. Under high gas pressure, radial strain remains dilative throughout, and volumetric strain decreases while remaining dilative. Both axial peak and residual strains grow exponentially in two stages (gradual increase then stabilization). Higher gas pressure accelerates mesoscopic structure adjustment and earlier strain stabilization. For energy partitioning, the fraction of elastic energy rises while dissipated energy falls with cycling. Higher gas pressure yields a larger average dissipated energy fraction, reflecting more energy consumed by irreversible damage. For seepage, loading-phase permeability decays exponentially with cycling, accumulating absolute permeability damage. Unloading-phase permeability increases progressively, showing a permeability enhancement effect that strengthens with gas pressure, reaching 5.4%, 16.3% and 26.7% at 1, 3 and 5 MPa respectively. Finally, a dynamic permeability evolution model is developed from the porosity and Kozeny-Carman equations, incorporating a cyclic damage attenuation coefficient and accounting for gas slippage, compression, and adsorption/thermal expansion. The model achieves good fit and accurately captures permeability evolution with cycles across gas pressures. These findings provide support for understanding the mechanical mechanism of coal-gas dynamic disasters.