Custom designed and built meso shear test equipment was used to examine the shear crack propagation in gassy coal under different gas pressures.The spatial-temporal evolution of gas migration pathways in the coal duri...Custom designed and built meso shear test equipment was used to examine the shear crack propagation in gassy coal under different gas pressures.The spatial-temporal evolution of gas migration pathways in the coal during shear loading was also researched.The results show that gas pressure can hasten crack growth at the shear fracture surface,can reduce the shear strength of gassy coal,and can accelerate the shear failure process.Shear failure in gassy coal exhibits five stages:the pre-crack stage;the stable crack growth stage;the unsteady crack growth stage;the fracture stage;and,finally,the friction crack stage.The shear breaking creates two kinds of crack,shear cracks and tensile cracks.Cracks first appear in the shear plane at both ends and then extend toward the center until a shear fracture surface forms.The direction of shear crack propagation diverges from the predetermined shear plane by an angle of about 5°-10°.展开更多
The mechanical properties of rocks under cyclic and dynamic loading are important research topics for solving the structural stability of large engineering rocks. As underground mining in coal mines goes deeper, groun...The mechanical properties of rocks under cyclic and dynamic loading are important research topics for solving the structural stability of large engineering rocks. As underground mining in coal mines goes deeper, ground stresses are increasing and instability damage of coal rocks by shear loading is frequent. Therefore, in order to investigate the shear mechanical properties and section morphological characteristics of intact coal samples in the direct shear test, the RDS-200 rock direct shear instrument was used to carry out direct shear tests on intact coal samples under different normal stresses, and the shear section was scanned for three-dimensional morphology. The results show that: 1) from the strength characteristics, the peak shear strength of the coal samples increased linearly with increasing normal stress, and the residual shear strength increased logarithmically. 2) In terms of deformation characteristics, the peak shear displacement of the coal sample increases linearly with increasing normal stress, the pre-peak shear stiffness increases logarithmically, and the residual normal displacement decreases linearly. 3) From the morphological characteristics of the shear surface, with the increase of normal stress, the section transitions from high-order undulating to flattening type. The maximum height of the fracture surface profile and kurtosis coefficient of the shear section decreased linearly, and the profile area ratio and root mean square of slope decreased as a power function, i.e. the higher the normal stress, the smaller the undulation of the section, the sharpness of the roughness shape and the roughness coefficient JRC, and the flatter and smoother the section. The findings of this study can help to provide some reference for the evaluation of shear instability occurring in coal bodies under different normal stresses.展开更多
基金supported in part by the State Key Basic Research Program of China(No.2011CB201203)in part by the General Project of the National Natural Science Foundation of China(No.50974141)the Fundamental Research Funds for the Central Universities(No.CDJZR12240055)
文摘Custom designed and built meso shear test equipment was used to examine the shear crack propagation in gassy coal under different gas pressures.The spatial-temporal evolution of gas migration pathways in the coal during shear loading was also researched.The results show that gas pressure can hasten crack growth at the shear fracture surface,can reduce the shear strength of gassy coal,and can accelerate the shear failure process.Shear failure in gassy coal exhibits five stages:the pre-crack stage;the stable crack growth stage;the unsteady crack growth stage;the fracture stage;and,finally,the friction crack stage.The shear breaking creates two kinds of crack,shear cracks and tensile cracks.Cracks first appear in the shear plane at both ends and then extend toward the center until a shear fracture surface forms.The direction of shear crack propagation diverges from the predetermined shear plane by an angle of about 5°-10°.
文摘The mechanical properties of rocks under cyclic and dynamic loading are important research topics for solving the structural stability of large engineering rocks. As underground mining in coal mines goes deeper, ground stresses are increasing and instability damage of coal rocks by shear loading is frequent. Therefore, in order to investigate the shear mechanical properties and section morphological characteristics of intact coal samples in the direct shear test, the RDS-200 rock direct shear instrument was used to carry out direct shear tests on intact coal samples under different normal stresses, and the shear section was scanned for three-dimensional morphology. The results show that: 1) from the strength characteristics, the peak shear strength of the coal samples increased linearly with increasing normal stress, and the residual shear strength increased logarithmically. 2) In terms of deformation characteristics, the peak shear displacement of the coal sample increases linearly with increasing normal stress, the pre-peak shear stiffness increases logarithmically, and the residual normal displacement decreases linearly. 3) From the morphological characteristics of the shear surface, with the increase of normal stress, the section transitions from high-order undulating to flattening type. The maximum height of the fracture surface profile and kurtosis coefficient of the shear section decreased linearly, and the profile area ratio and root mean square of slope decreased as a power function, i.e. the higher the normal stress, the smaller the undulation of the section, the sharpness of the roughness shape and the roughness coefficient JRC, and the flatter and smoother the section. The findings of this study can help to provide some reference for the evaluation of shear instability occurring in coal bodies under different normal stresses.
