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By using MTS815 equipment and 12 CHs PCI-2 acoustic emission acquisition system, the acoustic emission (AE) characteristics of rock under tiered cyclic loading and cyclic loading during complete failure process under uniaxial compression were studied, and the Kaiser effect and the Felicity effect and the standard of acoustic emission increasing obviously on Felicity effect were discussed. The results show that: the existence of Kaiser effect is valid, but it is bound and the upper limit of stress level under which Kaiser effect exists is 70% of the peak stress; after that, memory characteristic of rock stress shows obvious Felicity effect; the Felicity ratio presents distinct characteristics of 3 stages and decreases in general; there is no impact on the evolutionary trend of Felicity ratio as long as the standard of obvious acoustic emission falls in a appropriate range. [ABSTRACT FROM AUTHOR]

An effective stress calculation formula was proposed for coal containing gas with considering the swelling stress of gas adsorption based on the effective stress principles for porous media. Referring to dynamic model of porosity and permeability in coal containing gas, solid-gas coupling model which could describe the skeleton deformability of coal containing gas and the compressibility of gas under the solid-gas interaction condition was built. First we made excavation on the three-dimensional model based on the physical parameters of Pingdingshan tenth coal mine to obtain the stress distribution of coal seam after excavated instead of easy uniform loading. Then we simulated the gas drainage from boreholes based on constructed mathematical model. From the results we got: (1) Negative pressure didn't have a great influence on gas drainage. (2) The porosity of coal seam decreased gradually over time. (3) The effective radius increased gradually to a fixed value over time. [ABSTRACT FROM AUTHOR]

Based on domestic-developed triaxial servo-controlled seepage equipment for thermal-hydrological-mechanical coupling of coal containing methane, the experimental study of unloading confining pressure of coal was performed on coal samples under different gas pressure. The results show that the characteristic of distinct dilatancy is displayed in the process of unloading confining pressure, therefore seepage channels in coal body are extended and seepage velocity increases. The deformation of coal containing methane per unit decreased confining pressure and seepage velocity increases with the increase in gas pressure in the same stress paths. The compressive strength decreases gradually with the increase of gas pressure. In the initial stage of unloading confining pressure, deformation modulus of coal containing methane changes little. After the yielding occurs, it decreases obviously. The deformation modulus decreases 3.71% -7.45% in the process of unloading confining pressure. Meanwhile, the Poisson's ratio turns to increase and a function can be used to describe the relationship between confining pressure and Poisson's ratio. [ABSTRACT FROM AUTHOR]