Failure mechanism and mining-induced mechanical properties of coal under different loading rates

Research on the mining-induced mechanical response and failure mechanism of coal under different loading modes and different loading rates is instructive for recognizing the nature of dynamic disaster in coal mines. Based on the coal samples from Tashan,the uniaxial tension and compression,conventional triaxial compression and mining-in- duced mechanical test have been conducted. The mechanical parameters and deformation characteristics under differ- ent loading modes were obtained. Furthermore,the comparative analysis of coal deformation between conventional triax- ial compression and mining-induced mechanical test was studied. The linear relationship between axial loading rate and absorbed energy intensity was obtained. The improved strength and absorbed energy intensity are caused by deviatoric stress,which can explain the time effects of damage. Considering the effective volume stress,the stress difference,the axial loading rate and confining pressure unloading rate,a new viscoelastic model with yield criterion is proposed to de- scribe the material yield strength changes caused by unloading rates.