A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strai...A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading rates.Investigated results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle response.When the loading rate is relatively high,the curve shows a more ductile response.Both of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface spalling.Moreover,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.展开更多
Fissures play a significant role in predicting the unstable failure of rock mass engineering.For deep rock underground engineering,rock mass containing pre-existing fissures is usually located in triaxial stress state...Fissures play a significant role in predicting the unstable failure of rock mass engineering.For deep rock underground engineering,rock mass containing pre-existing fissures is usually located in triaxial stress state.Therefore,not only pre-existing fissure but also confining pressure affects the failure mechanical behavior of rock material.In this research,the granite specimens containing two non-coplanar open fissures were investigated by a series of conventional triaxial compression tests.First,the effect of bridge angle and confining pressure on strength and deformation characteristics of granite specimens was evaluated.Results show that the triaxial compressive strength,failure axial strain,and crack damage threshold increased nonlinearly with confining pressure.Under high confining pressures,elastic modulus was insensitive to bridge angle.Then,an X-ray micro-CT scanning technique was used to analyze the internal fracture characteristics of granite specimens with respect to various bridge angles and confining pressures.Five typical crack coalescence modes were identified,namely,indirect coalescence,shear coalescence and three types of tensile coalescence.The reconstructed 3-D CT images indicated that under uniaxial or low confining pressures,the bridge angle had a significant effect on crack evolution behavior,while under high confining pressures,shear-dominated failures occurred with the development of anti-wing cracks.展开更多
基金Project(BK20150005) supported by the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars,ChinaProject(2014YC10) supported by the Fundamental Research Funds for the Central Universities,China
文摘A series of laboratory experiments and PFC numerical simulations for rock-like material specimens containing two unparallel fissures were carried out.On the basis of experimental and numerical results,the stress-strain curves,mechanical properties,AE events,cracking behavior and energy characteristics were analyzed to reveal the macro-mechanical behavior and meso-mechanism of pre-fissured specimens under different loading rates.Investigated results show that:1)When the loading rate is relatively low,the stress-strain curves show a brittle response.When the loading rate is relatively high,the curve shows a more ductile response.Both of the peak strength and elastic mudulus increase with the increase of loading rate,which can be expressed as power functions.2)Four crack types are identified,i.e.,tensile crack,shear crack,far-field crack and surface spalling.Moreover,the tensile crack,far-field crack and surface spalling are under tensile mechanism,while the shear crack is under shear mechanism.3)The drops of the stress-strain curves all correspond to the crack initiation or coalescence,which is also linked to a sudden increasing in the accumulated micro-crack curve.4)Both of the maximum bond force and energy have the similar trend with the increase of loading rate to peak strength,which indicates that the trend of peak strength can be explained by the meso-mechanics and energy.
基金Project(42077231) supported by the National Natural Science Foundation of China。
文摘Fissures play a significant role in predicting the unstable failure of rock mass engineering.For deep rock underground engineering,rock mass containing pre-existing fissures is usually located in triaxial stress state.Therefore,not only pre-existing fissure but also confining pressure affects the failure mechanical behavior of rock material.In this research,the granite specimens containing two non-coplanar open fissures were investigated by a series of conventional triaxial compression tests.First,the effect of bridge angle and confining pressure on strength and deformation characteristics of granite specimens was evaluated.Results show that the triaxial compressive strength,failure axial strain,and crack damage threshold increased nonlinearly with confining pressure.Under high confining pressures,elastic modulus was insensitive to bridge angle.Then,an X-ray micro-CT scanning technique was used to analyze the internal fracture characteristics of granite specimens with respect to various bridge angles and confining pressures.Five typical crack coalescence modes were identified,namely,indirect coalescence,shear coalescence and three types of tensile coalescence.The reconstructed 3-D CT images indicated that under uniaxial or low confining pressures,the bridge angle had a significant effect on crack evolution behavior,while under high confining pressures,shear-dominated failures occurred with the development of anti-wing cracks.
