In order to study the failure of surrounding rock under high in situ stress in deep underground engineering projects, disturbed by excavation unloading, we carried out triaxial unloading experiments using thickwalled ...In order to study the failure of surrounding rock under high in situ stress in deep underground engineering projects, disturbed by excavation unloading, we carried out triaxial unloading experiments using thickwalled cylinder specimens on a TATW-2000 rock servo-controlled triaxial testing machine in a laboratory. The specimens were made of limestone material, taken from Tongshan county, Xuzhou city, Jiangsu province, China. In our experiments, rock deformation and failure behavior was studied through loading and unloading of inner hole pressure of thick-walled cylinder specimens. At first, the axial stress, confining pressure and inner pressure were increased simultaneously to a specified designed state of stress. Then, keeping the axial stress and confining pressure stable, the pressure on the inner hole was decreased until the specimen was fractured. When the inner pressure was released completely but the specimen did not fracture, the confining pressure was decreased subsequently until complete failure occurred. Our experimental results suggest that traces of major circular ringlike fractures with a number of radial cracks often appear in thick cylinder walls. This type of ringlike failure phenomenon, similar to intermittent zonal fracturing characteristics of deep exploitation, has, so far, not been published. Our experimental results show that rock deformation and failure behavior of thick-walled limestone cylinders vary under different stress paths between loading and unloading. Tensile failure and orderly failure surfaces occur under unloading conditions while irregular damaged rock blocks are produced during loading failure. This type of triaxial unloading experiment provides for new research methodology and approach for thorough investigations on intermittent zonal fracturing in deep underground excavations.展开更多
In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specime...In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specimens of different widths that include a prefabricated crack on either a single side to facilitate unilateral crack propagation, or prefabricated cracks positioned on both sides asymmetrically with respect to the specimen midpoint to facilitate bilateral crack propagation under direct tensile stress with a loading rate of 0.001 mm/s. The results show that the main pathways of unilateral crack propagation governing specimen failure are fluctuated locally, but present an approximately straight line overall in the absence of pre-existing internal defects. However, the pathways of bilateral crack propagation are relatively complex, although they present similar characteristics. Analysis results suggest that bilateral crack propagation can be basically divided into three stages, i.e. a stage of linear propagation, a stage representing deviation from the other crack, and a stage where one crack approaches either the other crack or approaches the opposite edge of the specimen, and thereby forming a continuous crack through the specimen. In addition, the stressestrain curves of bilateral crack specimens do not vary significantly around the point of peak stress prior to specimen failure, which means that the specimens do not fail instantaneously.展开更多
The commercial finite element package ANSYSTM was utilized for prediction of temperature distribution during reheating treatment of hot torsion test （HTT） samples with different geometries for API-X70 microalloyed s...The commercial finite element package ANSYSTM was utilized for prediction of temperature distribution during reheating treatment of hot torsion test （HTT） samples with different geometries for API-X70 microalloyed steel. Simulation results show that an inappropriate choice of test specimen geometry and reheating conditions before deformation could lead to non-uniform temperature distribution within the gauge section of specimen. Therefore, assumptions of isothermal experimental conditions and zero temperature gradient within the specimen cross section appear unjustified and led to uncertainties of flow curve obtained. Recommendations on finding proper specimen geometry for reducing temperature gradient along the gauge part of specimen will be given to create homogeneous initial microstructure as much as possible before deformation in order to avoid uncertainty in consequent results of HTT.展开更多
Aim To improve the efficiency of fatigue material tests and relevant statistical treatment of test data. Methods\ Least square approach and other special treatments were used. Results and Conclusion\ The concepts...Aim To improve the efficiency of fatigue material tests and relevant statistical treatment of test data. Methods\ Least square approach and other special treatments were used. Results and Conclusion\ The concepts of each phase in fatigue tests and statistical treatment are clarified. The method proposed leads to three important properties. Reduced number of specimens brings to the advantage of lowering test expenditures. The whole test procedure has more flexibility for there is no need to conduct many tests at the same stress level as in traditional cases.展开更多
试件尺度的岩石受载破裂过程中,其本身结构发生变形、破坏的同时,包含了地球物理属性参数信息的变化,如应变量、电阻率、波速等。通过对受载中的岩石试件进行地球物理参数测试,可定性或定量地感知其内部结构、强度等特征变化,有助于了...试件尺度的岩石受载破裂过程中,其本身结构发生变形、破坏的同时,包含了地球物理属性参数信息的变化,如应变量、电阻率、波速等。通过对受载中的岩石试件进行地球物理参数测试,可定性或定量地感知其内部结构、强度等特征变化,有助于了解岩石试件破裂机理,进而解决一系列岩体工程测试问题。基于Web of Science论文检索系统搜索出岩石试件加载测试的文献资料,利用CiteSpace软件对岩石试件加载测试现状进行分析,并详细阐述了几种常用测试方法的原理及研究进展。结合煤系地层深部采场领域研究现状,分析、总结岩石试件受载测试研究过程中存在的不足,并对地球物理参数采集、装置研发与微-宏观测试融合等方面提出展望。展开更多
基金supported by the National Natural Science Foundation of China (Nos.50804046, 50490273 and 50774082)the Scientific Research Fund for Youths of CUMT (No. 0B080240)
文摘In order to study the failure of surrounding rock under high in situ stress in deep underground engineering projects, disturbed by excavation unloading, we carried out triaxial unloading experiments using thickwalled cylinder specimens on a TATW-2000 rock servo-controlled triaxial testing machine in a laboratory. The specimens were made of limestone material, taken from Tongshan county, Xuzhou city, Jiangsu province, China. In our experiments, rock deformation and failure behavior was studied through loading and unloading of inner hole pressure of thick-walled cylinder specimens. At first, the axial stress, confining pressure and inner pressure were increased simultaneously to a specified designed state of stress. Then, keeping the axial stress and confining pressure stable, the pressure on the inner hole was decreased until the specimen was fractured. When the inner pressure was released completely but the specimen did not fracture, the confining pressure was decreased subsequently until complete failure occurred. Our experimental results suggest that traces of major circular ringlike fractures with a number of radial cracks often appear in thick cylinder walls. This type of ringlike failure phenomenon, similar to intermittent zonal fracturing characteristics of deep exploitation, has, so far, not been published. Our experimental results show that rock deformation and failure behavior of thick-walled limestone cylinders vary under different stress paths between loading and unloading. Tensile failure and orderly failure surfaces occur under unloading conditions while irregular damaged rock blocks are produced during loading failure. This type of triaxial unloading experiment provides for new research methodology and approach for thorough investigations on intermittent zonal fracturing in deep underground excavations.
基金support provided by the Strategic Program of Chinese Academy of Sciences (Grant No. XDB10030400)the Hundred Talent Program of Chinese Academy of Sciences (Grant No. Y323081C01)
文摘In this paper, a compression-to-tension conversion technique is developed by applying predominant mode I loading test, using a servo-controlled compression system. The technique is applied to thin mortar plate specimens of different widths that include a prefabricated crack on either a single side to facilitate unilateral crack propagation, or prefabricated cracks positioned on both sides asymmetrically with respect to the specimen midpoint to facilitate bilateral crack propagation under direct tensile stress with a loading rate of 0.001 mm/s. The results show that the main pathways of unilateral crack propagation governing specimen failure are fluctuated locally, but present an approximately straight line overall in the absence of pre-existing internal defects. However, the pathways of bilateral crack propagation are relatively complex, although they present similar characteristics. Analysis results suggest that bilateral crack propagation can be basically divided into three stages, i.e. a stage of linear propagation, a stage representing deviation from the other crack, and a stage where one crack approaches either the other crack or approaches the opposite edge of the specimen, and thereby forming a continuous crack through the specimen. In addition, the stressestrain curves of bilateral crack specimens do not vary significantly around the point of peak stress prior to specimen failure, which means that the specimens do not fail instantaneously.
文摘The commercial finite element package ANSYSTM was utilized for prediction of temperature distribution during reheating treatment of hot torsion test （HTT） samples with different geometries for API-X70 microalloyed steel. Simulation results show that an inappropriate choice of test specimen geometry and reheating conditions before deformation could lead to non-uniform temperature distribution within the gauge section of specimen. Therefore, assumptions of isothermal experimental conditions and zero temperature gradient within the specimen cross section appear unjustified and led to uncertainties of flow curve obtained. Recommendations on finding proper specimen geometry for reducing temperature gradient along the gauge part of specimen will be given to create homogeneous initial microstructure as much as possible before deformation in order to avoid uncertainty in consequent results of HTT.
文摘Aim To improve the efficiency of fatigue material tests and relevant statistical treatment of test data. Methods\ Least square approach and other special treatments were used. Results and Conclusion\ The concepts of each phase in fatigue tests and statistical treatment are clarified. The method proposed leads to three important properties. Reduced number of specimens brings to the advantage of lowering test expenditures. The whole test procedure has more flexibility for there is no need to conduct many tests at the same stress level as in traditional cases.
文摘试件尺度的岩石受载破裂过程中,其本身结构发生变形、破坏的同时,包含了地球物理属性参数信息的变化,如应变量、电阻率、波速等。通过对受载中的岩石试件进行地球物理参数测试,可定性或定量地感知其内部结构、强度等特征变化,有助于了解岩石试件破裂机理,进而解决一系列岩体工程测试问题。基于Web of Science论文检索系统搜索出岩石试件加载测试的文献资料,利用CiteSpace软件对岩石试件加载测试现状进行分析,并详细阐述了几种常用测试方法的原理及研究进展。结合煤系地层深部采场领域研究现状,分析、总结岩石试件受载测试研究过程中存在的不足,并对地球物理参数采集、装置研发与微-宏观测试融合等方面提出展望。
