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.

In this paper, we investigated the mechanics and permeation properties of the raw coal sample during loading and unloading process, and come to some conclusions: the permeability of the sample increases nonlinearly during the unloading confining pressure process. The larger the gas pressure is, the greater the increase range of the permeability will be. The larger the confining pressure unloading amplitude is, the greater the increase range of the permeability will be. In the loading process, the permeability and the axial strain of the specimen change in a “V” shape. As the gas pressure increases, the peak strength of the specimen gradually decreases, and fitted the gas pressure and the peak strength are accordance with the linear relationship. As the confining pressure increase, the peak strength of the sample gradually increases, and fitted the confining pressure and the peak strength are accordance with the exponential function. The internal friction angle of the coal sample was 43.22°, and the cohesion was 3.77 MPa. The relationship between the fitted gas pressure and internal friction angle, gas pressure and cohesion is in line with linear functions. Maintain an axial stress constant, unloaded confining pressure to a constant state of target value, the permeability of specimen shows a constant pressure boosting flow zone, the relationship between permeability and deviatoric stress is accordance with the ExpDec1 function during the process of unloading confining pressure and prepeak loading axial stress.

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 b value and power-law exponent, respectively. The results of statistical evolution of acoustic emission energy showed that the b 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 b 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.