Mechanical failure mechanisms and forms of normal and deformed coal combination containing gas: Model development and analysis

Experimental study on strain behavior and permeability evolution of sandstone under constant amplitude cyclic loading‐unloading

“…27 These effective seepage channels may not change regularly with a change in v and N. The evolution of normalized permeability may be related to the dilatancy capacity between adjacent cyclic loading-unloading. 34,35 Combined with the experimental results, when the engineering activities are conducted at mining depths of kilometer levels or the special rock formations, such as the top coal caving 36,37 and large mining height technology, 38,39 it is necessary to design the advance rate such that the rate level is sufficiently low to prevent rockburst, and yet high enough to prevent coal and gas outburst. However, no significant fatigue damage was produced due to the smaller prepeak axial stress than the peak strength.…”

“…33 Furthermore, high in situ stress (ie, the increase in initial confining pressure in experiment) determines the greater ultimate energystorage capacity of the rock, which increases the possibility of rockburst. 34,35 Combined with the experimental results, when the engineering activities are conducted at mining depths of kilometer levels or the special rock formations, such as the top coal caving 36,37 and large mining height technology, 38,39 it is necessary to design the advance rate such that the rate level is sufficiently low to prevent rockburst, and yet high enough to prevent coal and gas outburst. It is worth noting that due to the inevitable discreteness and heterogeneity between the tested sandstone specimens, the permeability increases with the loading rate and then decreases at σ 3 = 10 MPa.…”

Damage‐induced permeability model of coal and its application to gas predrainage in combination of soft coal and hard coal

“…Therefore, Chinese scholars pay more attention to the study of the permeability evolution after the stress‐induced plastic failure of coal . According to the Mohr–coulomb failure criterion, the loading stress path and unloading stress path both can make the coal be damaged . For the loading stress path, Yang et al, Wang et al, and Xue et al experimentally studied the change law of damage‐induced permeability due to loading stress in the process of the complete stress–strain of coal samples.…”

“…15,16 According to the Mohr-coulomb failure criterion, the loading stress path and unloading stress path both can make the coal be damaged. 17,18 For the loading stress path, Yang et al, 19 Wang et al, 20,21 and Xue et al [22][23][24][25] experimentally studied the change law of damage-induced permeability due to loading stress in the process of the complete stress-strain of coal samples. For the unloading stress path, Yin et al, [26][27][28][29] Xu et al, 30 and Zhang et al 31 carried out a large number of experiments to analyze the influencing factors such as style of loading stress path, speed of unloading stress, and cyclic unloading stress on coal permeability.…”

Hydraulic flushing in soft coal sublayer: Gas extraction enhancement mechanism and field application

“…In China, many soft coal mass only develops as one or several ultrathin sublayers in the coal seam. Lu et al pointed out that this kind of coal seam is of greater coal and gas outburst risk due to the fact that uncoordinated horizontal deformation always occurs at the interface between the soft sublayer and the hard sublayer. However, little attention has been paid to the gas extraction in this special kind of coal seam.…”