Tackling the problems of underground water storage in collieries in arid regions requires knowledge of the effect of water intrusion and loading rate on the mechanical properties of and crack development in coal–rock...Tackling the problems of underground water storage in collieries in arid regions requires knowledge of the effect of water intrusion and loading rate on the mechanical properties of and crack development in coal–rock combinations. Fifty-four coal–rock combinations were prepared and split equally into groups containing different moisture contents(dry, natural moisture and saturated) to conduct acoustic emission testing under uniaxial compression with loading rates ranging from 0.1 mm/min to 0.6 mm/min. The results show that the peak stress and strength-softening modulus, elastic modulus, strain-softening modulus, and post-peak modulus partly decrease with increasing moisture content and loading rate. In contrast, peak strain increases with increasing moisture content and fluctuates with rising loading rate. More significantly, the relationship between stiffness and stress, combined with accumulated counts of acoustic emission, can be used to precisely predict all phases of crack propagation. This is helpful in studying the impact of moisture content and loading rate on crack propagation and accurately calculating mechanical properties. We also determined that the stress thresholds of crack closure, crack initiation, and crack damage do not vary with changes of moisture content and loading rate, constituting 15.22%, 32.20%, and 80.98% of peak stress, respectively. These outcomes assist in developing approaches to water storage in coal mines, determining the necessary width of waterproof coal–rock pillars, and methods of supporting water-enriched roadways, while also advances understanding the mechanical properties of coal–rock combinations and laws of crack propagation.展开更多
The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on sub...The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on subcritical crack growth. With water-rock interaction, the crack velocity increases, while the stress intensity factor declines, which illustrates that water-rock interaction can decrease the strength of rocks and accelerate the subcritical crack growth. Based on Charlse theory and Hilling & Charlse theory, the test data were analyzed by regression and the correlation coefficients were all higher than 0.7, which shows the correlation is significant. This illustrates that both theories can explain the results of tests very well. Therefore, it is believed that the subcritical crack growth attributes to the breaking of chemical bond, which is caused by the combined effect of the tensile stress and the chemical reaction between the material at crack tip and the corrosive agent. Meanwhile, water-rock interaction has a vital effect on fracture toughness. The fracture toughness of samples under atmospheric environment is higher than that of samples immersed in water. And water-rock interaction has larger influence on fracture toughness in amphibolite than that in peridotite and lherzolite.展开更多
In worldwide,the most common triggering factor of rock landslides is extended and intense rainfall.However,different from the soil slope failure caused by softening action of infiltration rainwater,the mechanism of ro...In worldwide,the most common triggering factor of rock landslides is extended and intense rainfall.However,different from the soil slope failure caused by softening action of infiltration rainwater,the mechanism of rock landslide in rainfall is not clear.From the view of fracture mechanics,the propagation of cracks on rock slope and the development of sliding surface were researched.Then based on hydraulics formulas and using Sweden arc method,the influence of crack water on stability of rock slope was quantitatively studied.Finally,an example was given to check the theoretical approach.The result shows that the development of sliding surface of rock slope is mainly caused by crack propagation under hydrostatic pressure when the stress intensity factor KI at crack tip is bigger than the toughness index of rock fractures KIC,and the failure of slope is the result of hydraulic action of crack water and the softening of materials on sliding surface when the depth of crack water is bigger than a minimum value hmin.展开更多
Five complete caverns were discovered in Longyou in 1992.They were manually caved in argillaceous siltstone at shallow depths more than 2000 years ago.When they were un-watered,their integrity was maintained completel...Five complete caverns were discovered in Longyou in 1992.They were manually caved in argillaceous siltstone at shallow depths more than 2000 years ago.When they were un-watered,their integrity was maintained completely,and their interior rock surfaces were free of old cracks.Since then,however,the rock's interior faces have initiated and propagated more and more cracks.This paper attempts to address the question of why the rock interior faces were free of old cracks once they were unearthed.To address this question,this paper proposes a hypothesis that the argillaceous siltstone has the ability of self-healing its cracks over a short period of time under weak acid water environment.Data and evidence are presented herewith to prove the hypothesis.They include observations and measurements in the field and test results in the laboratory.Specifically,a three-point bending test is used to form a tensile crack in a rectangular rock specimen and a deadload test for the specimen immersed in initially weak acid water is used for self-healing its crack.The results have shown that the argillaceous siltstone is in a state of weak alkalinity and the rain water at the site is in a state of weak acidity.Therefore,when it is immersed in weak acid water for some time,the argillaceous siltstone would be able to make chemical reactions to generate new minerals such as calcite.The new minerals would be able to infill the cracks and then heal the crack within a few years.Once the crack is self-healed,the rock can regain its strength and integrity.Consequently,the rock interior surfaces could be free of old cracks when the water was pumped out of the caverns.展开更多
基金Project(2014QNB31)supported by the Fundamental Research Funds for the Central Universities,ChinaProjects(51674248)supported by the National Natural Science Foundation of ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD),China
文摘Tackling the problems of underground water storage in collieries in arid regions requires knowledge of the effect of water intrusion and loading rate on the mechanical properties of and crack development in coal–rock combinations. Fifty-four coal–rock combinations were prepared and split equally into groups containing different moisture contents(dry, natural moisture and saturated) to conduct acoustic emission testing under uniaxial compression with loading rates ranging from 0.1 mm/min to 0.6 mm/min. The results show that the peak stress and strength-softening modulus, elastic modulus, strain-softening modulus, and post-peak modulus partly decrease with increasing moisture content and loading rate. In contrast, peak strain increases with increasing moisture content and fluctuates with rising loading rate. More significantly, the relationship between stiffness and stress, combined with accumulated counts of acoustic emission, can be used to precisely predict all phases of crack propagation. This is helpful in studying the impact of moisture content and loading rate on crack propagation and accurately calculating mechanical properties. We also determined that the stress thresholds of crack closure, crack initiation, and crack damage do not vary with changes of moisture content and loading rate, constituting 15.22%, 32.20%, and 80.98% of peak stress, respectively. These outcomes assist in developing approaches to water storage in coal mines, determining the necessary width of waterproof coal–rock pillars, and methods of supporting water-enriched roadways, while also advances understanding the mechanical properties of coal–rock combinations and laws of crack propagation.
基金Project(51374246,51474249)supported by the National Natural Science Foundation of ChinaProject(2013FJ6002)supported by the Science-Technology Project of Science-Technology Department of Hunan Province,China
文摘The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on subcritical crack growth. With water-rock interaction, the crack velocity increases, while the stress intensity factor declines, which illustrates that water-rock interaction can decrease the strength of rocks and accelerate the subcritical crack growth. Based on Charlse theory and Hilling & Charlse theory, the test data were analyzed by regression and the correlation coefficients were all higher than 0.7, which shows the correlation is significant. This illustrates that both theories can explain the results of tests very well. Therefore, it is believed that the subcritical crack growth attributes to the breaking of chemical bond, which is caused by the combined effect of the tensile stress and the chemical reaction between the material at crack tip and the corrosive agent. Meanwhile, water-rock interaction has a vital effect on fracture toughness. The fracture toughness of samples under atmospheric environment is higher than that of samples immersed in water. And water-rock interaction has larger influence on fracture toughness in amphibolite than that in peridotite and lherzolite.
基金Project(2008CB425802) supported by the National Basic Research Program of China Project(40872181) supported by the National Natural Science Foundation of ChinaProject(09R2200200) supported by the West Light Foundation of Chinese Academy of Sciences
文摘In worldwide,the most common triggering factor of rock landslides is extended and intense rainfall.However,different from the soil slope failure caused by softening action of infiltration rainwater,the mechanism of rock landslide in rainfall is not clear.From the view of fracture mechanics,the propagation of cracks on rock slope and the development of sliding surface were researched.Then based on hydraulics formulas and using Sweden arc method,the influence of crack water on stability of rock slope was quantitatively studied.Finally,an example was given to check the theoretical approach.The result shows that the development of sliding surface of rock slope is mainly caused by crack propagation under hydrostatic pressure when the stress intensity factor KI at crack tip is bigger than the toughness index of rock fractures KIC,and the failure of slope is the result of hydraulic action of crack water and the softening of materials on sliding surface when the depth of crack water is bigger than a minimum value hmin.
基金The authors would like to thank financial supports from the National Natural Science Foundation of China(Grant Nos.42272122 and 40902088).
文摘Five complete caverns were discovered in Longyou in 1992.They were manually caved in argillaceous siltstone at shallow depths more than 2000 years ago.When they were un-watered,their integrity was maintained completely,and their interior rock surfaces were free of old cracks.Since then,however,the rock's interior faces have initiated and propagated more and more cracks.This paper attempts to address the question of why the rock interior faces were free of old cracks once they were unearthed.To address this question,this paper proposes a hypothesis that the argillaceous siltstone has the ability of self-healing its cracks over a short period of time under weak acid water environment.Data and evidence are presented herewith to prove the hypothesis.They include observations and measurements in the field and test results in the laboratory.Specifically,a three-point bending test is used to form a tensile crack in a rectangular rock specimen and a deadload test for the specimen immersed in initially weak acid water is used for self-healing its crack.The results have shown that the argillaceous siltstone is in a state of weak alkalinity and the rain water at the site is in a state of weak acidity.Therefore,when it is immersed in weak acid water for some time,the argillaceous siltstone would be able to make chemical reactions to generate new minerals such as calcite.The new minerals would be able to infill the cracks and then heal the crack within a few years.Once the crack is self-healed,the rock can regain its strength and integrity.Consequently,the rock interior surfaces could be free of old cracks when the water was pumped out of the caverns.
