Mechanical criterion for coal and gas outburst:a perspective from multiphysics coupling

Although a series of hypotheses have been proposed,the mechanism underlying coal and gas outburst remains unclear.Given the low-index outbursts encountered in mining practice,we attempt to explore this mechanism using a multiphysics coupling model considering the effects of coal strength and gas mass transfer on failure.Based on force analysis of coal ahead of the heading face,a risk identification index C_(m)and a critical criterion(C_(m)≥1)of coal instability are proposed.According to this criterion,the driving force of an outburst consists of stress and gas pressure gradients along the heading direction of the roadway,whereas resistance depends on the shear and tensile strengths of the coal.The results show that outburst risk decreases slightly,followed by a rapid increase,with increasing vertical stress,whereas it decreases with increasing coal strength and increases with gas pressure monotonically.Using the response surface method,a coupled multi-factor model for the risk identification index is developed.The results indicate strong interactions among the controlling factors.Moreover,the critical values of the factors corresponding to outburst change depending on the environment of the coal seams,rather than being constants.As the buried depth of a coal seam increases,the critical values of gas pressure and coal strength decrease slightly,followed by a rapid increase.According to its controlling factors,outburst can be divided into stress-dominated,coal-strength-dominated,gas-pressure-dominated,and multi-factor compound types.Based on this classification,a classified control method is proposed to enable more targeted outburst prevention.

Research advances in non-Darcy flow in low permeability media

More and more experimental results show that Darcy’s law is not fully applicable in low permeability media,and non-Darcy flow has been identified.In this paper we reviewed the research of non-Darcy flow experiments in low-permeability media in recent decades,discuss the existence of non-Darcy flow,and summarize its constitutive equations.The reasons for the threshold gradient were also discussed and summarized for the criterion of the critical point of non-Darcy flow.On this basis,the future development of non-Darcy flow experiments in the rock and clay media were discussed,in order to provide a certain reference for subsequent research on seepage laws in low permeability media.

Coal and rock dynamic disaster prevention and control technology in the large mining face of a deep outburst mine

In this study, we systematically studied the occurrence regularity of in situ stress in the Pingdingshan mine. The critical criterion model of coal-rock destabilization was established based on the theoretical framework of fracture mechanics. Furthermore, we analyzed the coupling destabilization mechanism of in situ stress and gas and studied the influence of the variation between original rock stress and mining-induced stress on the critical criterion. Through field experiments and applications, we established a three-dimensional gas drainage technology system for areas with a large mining height and long work face. Based on our research, a demonstration project was developed for deep mine dynamic disaster control. The technical system included the arrangement and optimization of pre-drainage holes along the coal seam, technology, and optimization of gas drainage through the bottom drainage tunnel and upper corner, gas drainage technology through sieve tubes, and a two plugging with one injection under pressure sealing technology. The implementation of the demonstration project effectively reduced the gas content and pressure of the coal seam in the deep mine, and the project increased the critical strength of the instability and failure of coal and rock.