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The disturbance caused by excavation to surrounding rock structures during underground mining under complex geological conditions at great depth induces rock failure due to the effect of stress concentration and unloading. Therefore, the design, construction and maintenance of structures (i.e., pillars, drifts, chambers) are based not only on peak strength, but also on postpeak behavior and, subsequently, residual strength of rocks. Therefore, better understanding the characteristic features of rock at the postpeak stage is of paramount importance for underground construction and ground support design activities. Argillaceous limestone specimens loaded to the residual phase in the conventional triaxial compression test under different initial confining pressures were continuously loaded by loading and unloading cycles. Analysis of the variation characteristics of stress and strain were complemented with acoustic emission (AE) monitoring for investigating the effects of the confining pressure and the loading and unloading cycles on the mechanical properties of the rock in the residual phase. Besides, the yielding premonition information about the rock in the loading confining pressure stage was analyzed and calculated. The results show that because the deformation during the axial loading mainly comes from the sliding between the fracture planes, the bearing capacity is related to not only the confining pressure, but also the unloading path; the elastic modulus in the axial elastic deformation stage is larger than the corresponding elastic modulus of the prepeak stage, and the axial deformation presents good feature of elastic–plastic deformation; the bearing capacity of rock in the residual phase was provided by the frictional sliding between the elastic rock block under confining pressure. The precursor information about the rock yielding to plastic deformation in the loading confining pressure test of the failure rock could be confirmed based on the evolution characteristics of the AE amplitude.

The safe and efficient operation of coal mines is inseparable from rational production deployment. As for outburst-prone coal mines, the production deployment is more complicated due to the introduction of gas disaster control processes, which can easily cause continuity tension and even coal and gas outburst accidents. Therefore, it is necessary to establish an evaluation system for the rationality of production deployment of outburst-prone coal mines. In this paper, based on the production experience of coal mines in Chongqing, China and the summaries of experts, a production deployment evaluation system with eleven indices for outburst-prone coal mines is established. In addition, a Bayesian network is used to establish a corresponding evaluation model. The result shows that the evaluation index system for the production deployment rationality of outburst-prone coal mines, which is composed of the excavation advance indices and the validity indices of regional measure engineering, can systematically diagnose the rationality of each link of the production deployment for outburst-prone coal mines. The results of the case study show that the established Bayesian network model can be used to evaluate the deployment rationality of outburst-prone coal mines. The sensitivity analysis shows that the development coal reserve is the most sensitive to the reasonable deployment of outburst-prone coal mines. The accident prediction and cause diagnosis through the posterior probability reasoning indicate that in the absence of other evidence, the most likely reason for the unreasonable mine deployment is the insufficient development coal reserve. The observations and findings in this research have considerable practical significance for the smooth production of outburst-prone coal mines with similar geological conditions.

The mechanical properties and seepage characteristics of gas-bearing coal evolve with changes in the loading pattern, which could reveal the evolution of permeability in a protected coal seam and allow gas extraction engineering work to be designed by using the effect of mining multiple protective seams. Tests on gas seepage in raw coal under three paths (stepped-cyclic, stepped-increasing-cyclic, and crossed-cyclic loading and unloading) were carried out with a seepage tester under triaxial stress conditions. The permeability was subjected to the dual influence of stress and damage accumulation. After being subjected to stress unloading and loading, the permeability of coal samples gradually decreased and the permeability did not increase before the stress exceeded the yield stage of the coal samples. The mining-enhanced permeability of the coal samples in the loading stage showed a three-phase increase with the growth of stress and the number of cycles and exhibited an N-shaped increase under the stepped-cyclic loading while it linearly increased under the other two paths in the unloading stage. With the increase of peak stress and the accumulation of damage in coal samples, the sensitivity of the permeability of coal samples to stress gradually declined. The relationship between the damage variable and the number of cycles conformed to the Boltzmann function.