When tunnel boring machines(TBMs)excavate through jointed rock masses,the cutting efficiency is strongly affected by the shear strength of joints,the mechanism of which,however,remains poorly understood.In this study,...When tunnel boring machines(TBMs)excavate through jointed rock masses,the cutting efficiency is strongly affected by the shear strength of joints,the mechanism of which,however,remains poorly understood.In this study,a series of disc-cutter indentation tests were conducted on granite rock mass specimens with different joint shear strengths.During the indentation,the cracking process was recorded by a digital image correlation(DIC)system.The deformation and strength of specimens,cracking behavior,rock breakage mode and cutting efficiency were quantitatively investigated.In addition,to investigate the combined effects of joint shear strength,orientation and spacing on the rock breakage mechanism,numerical rock mass models were established based on a particle flow code PFC2D.Experimental results reveal that the cracking of primary and secondary cracks changes from the mixed shear-tensile to tensile mode in the initial stage,while the joint shear strength does not affect the cracking mode in the subsequent propagation process.The rock breakage mode is classified to an internal block breakage mode,a cross-joint breakage mode and a cutters-dependent breakage mode.The cross-joint breakage mode is optimal for improving the cutting efficiency.Numerical simulation results reveal that the increase in the joint shear strength changes the internal block breakage mode to cross-joint breakage mode for rock masses of particular ranges of joint orientation and spacing.These findings provide basis for improving the TBM cutting efficiency through jointed rock masses.展开更多
Demand is growing for explosive-free rock breakage systems for civil and mining engineering, and space industry applications. This paper highlights the work being undertaken in the Geomechanics Laboratory of Mc Gill U...Demand is growing for explosive-free rock breakage systems for civil and mining engineering, and space industry applications. This paper highlights the work being undertaken in the Geomechanics Laboratory of Mc Gill University to make a real application of microwave-assisted mechanical rock breakage to fullface tunneling machines and drilling. Comprehensive laboratory tests investigated the effect of microwave radiation on temperature profiles and strength reduction in hard rocks(norite, granite, and basalt)for a range of exposure times and microwave power levels. The heating rate on the surface of the rock specimens linearly decreased with distance between the sample and the microwave antenna, regardless of microwave power level and exposure time. Tensile and uniaxial compressive strengths were reduced with increasing exposure time and power level. Scanning electron micrographs(SEMs) highlighted fracture development in treated basalt. It was concluded that the microwave power level has a strong positive influence on the amount of heat damage induced to the rock surface. Numerical simulations of electric field intensity and wave propagation conducted with COMSOL Multiphysics~ software generated temperature profiles that were in close agreement with experimental results.展开更多
It has been an established fact that comminution processes, crushing and grinding, are most energy intensive processes which account for more than half of the total energy consumed in mineral industries.Various altern...It has been an established fact that comminution processes, crushing and grinding, are most energy intensive processes which account for more than half of the total energy consumed in mineral industries.Various alternative pre-treatment methods have been tried by experts around the globe. Although these methods yielded positive results in terms of reduction in energy consumption in crushing and particularly, in grinding operations at laboratory scale, their industrial application still remains an unresolved issue and challenge. Present review paper describes each one of these methods along with outcome of earlier studies and issues that need to be addressed through further rigorous experimental investigation.It also suggests the direction in which future studies can be carried out to meet the primary objective of making comminution processes more energy efficient than today they are.展开更多
The numerical simulation method to study rock breaking process and mechanism under high pressure water jet was developed with the continuous mechanics and the FEM theory. The rock damage model and the damage-coupling ...The numerical simulation method to study rock breaking process and mechanism under high pressure water jet was developed with the continuous mechanics and the FEM theory. The rock damage model and the damage-coupling model suited to analyze the whole process of water jet breaking rock were established with continuum damage mechanics and micro damage mechanics. The numerical results show the dynamic response of rock under water jet and the evolvement of hydrodynamic characteristic of jet during rock breaking is close to reality, and indicates that the body of rock damage and breakage under the general continual jet occurs within several milliseconds, the main damage form is tensile damage caused by rock unload and jet impact, and the evolvement of rock damage shows a step-change trend. On the whole, the numerical results can agree with experimental conclusions, which manifest that the analytical method is feasible and can be applied to guide the research and application of jet breaking rock theory.展开更多
Microwave precondition has been highlighted as a promising technology for softening the rock mass prior to rock breakage by machine to reduce drill bit/cutter wear as well as inverse production rate.To numerically exp...Microwave precondition has been highlighted as a promising technology for softening the rock mass prior to rock breakage by machine to reduce drill bit/cutter wear as well as inverse production rate.To numerically explore the effect of numerical parameters on rock static strength simulation,and determine the numerical mechanical parameters of microwave-treated basalts for future drilling and cutting simulations,numerical models of uniaxial compression strength(UCS)and Brazilian tensile strength(BTS)were established with the coupling of smoothed particle hydrodynamics and finite element method(SPH-FEM).To eliminate the large rock strength errors caused by microwave-induced damage,the cohesion and internal friction angle of microwave-treated basalt specimens with the same microwave treatment parameters were calibrated based on a linear Mohr-Coulomb theory.Based on parametric sensitivity analysis of SPH simulation of UCS and BTS,experimental UCS and BTS values were simultaneously captured according to the same set of calibrated cohesion and internal friction angle data,and the UCS modeling results are in good agreement with experimental tests.Furthermore,the effect of microwave irradiation parameter on the basalt mechanical behaviors was evaluated.展开更多
基金The financial support from the National Natural Science Foundation of China(Grant Nos.41831290,41907167 and 51708354)Natural Science Foundation of Zhejiang Province(Grant No.LTGS23E040001)Natural Science Foundation of Hunan Province(Grant No.2022JJ40521)is greatly appreciated.
文摘When tunnel boring machines(TBMs)excavate through jointed rock masses,the cutting efficiency is strongly affected by the shear strength of joints,the mechanism of which,however,remains poorly understood.In this study,a series of disc-cutter indentation tests were conducted on granite rock mass specimens with different joint shear strengths.During the indentation,the cracking process was recorded by a digital image correlation(DIC)system.The deformation and strength of specimens,cracking behavior,rock breakage mode and cutting efficiency were quantitatively investigated.In addition,to investigate the combined effects of joint shear strength,orientation and spacing on the rock breakage mechanism,numerical rock mass models were established based on a particle flow code PFC2D.Experimental results reveal that the cracking of primary and secondary cracks changes from the mixed shear-tensile to tensile mode in the initial stage,while the joint shear strength does not affect the cracking mode in the subsequent propagation process.The rock breakage mode is classified to an internal block breakage mode,a cross-joint breakage mode and a cutters-dependent breakage mode.The cross-joint breakage mode is optimal for improving the cutting efficiency.Numerical simulation results reveal that the increase in the joint shear strength changes the internal block breakage mode to cross-joint breakage mode for rock masses of particular ranges of joint orientation and spacing.These findings provide basis for improving the TBM cutting efficiency through jointed rock masses.
基金the Natural Sciences and Engineering Research Council of Canada(NSERC)with the collaboration of IAMGold,Glencore,and Vale Canada,who generously contributed financially to this research project
文摘Demand is growing for explosive-free rock breakage systems for civil and mining engineering, and space industry applications. This paper highlights the work being undertaken in the Geomechanics Laboratory of Mc Gill University to make a real application of microwave-assisted mechanical rock breakage to fullface tunneling machines and drilling. Comprehensive laboratory tests investigated the effect of microwave radiation on temperature profiles and strength reduction in hard rocks(norite, granite, and basalt)for a range of exposure times and microwave power levels. The heating rate on the surface of the rock specimens linearly decreased with distance between the sample and the microwave antenna, regardless of microwave power level and exposure time. Tensile and uniaxial compressive strengths were reduced with increasing exposure time and power level. Scanning electron micrographs(SEMs) highlighted fracture development in treated basalt. It was concluded that the microwave power level has a strong positive influence on the amount of heat damage induced to the rock surface. Numerical simulations of electric field intensity and wave propagation conducted with COMSOL Multiphysics~ software generated temperature profiles that were in close agreement with experimental results.
基金the support provided by Indian Institute of Technology,Kharagpur
文摘It has been an established fact that comminution processes, crushing and grinding, are most energy intensive processes which account for more than half of the total energy consumed in mineral industries.Various alternative pre-treatment methods have been tried by experts around the globe. Although these methods yielded positive results in terms of reduction in energy consumption in crushing and particularly, in grinding operations at laboratory scale, their industrial application still remains an unresolved issue and challenge. Present review paper describes each one of these methods along with outcome of earlier studies and issues that need to be addressed through further rigorous experimental investigation.It also suggests the direction in which future studies can be carried out to meet the primary objective of making comminution processes more energy efficient than today they are.
基金Project supported by the National Natural Science Foundation of China (Nos.50574062 and 50234030) the Post-Doctoral Science Foundation of China (No.2004035692)
文摘The numerical simulation method to study rock breaking process and mechanism under high pressure water jet was developed with the continuous mechanics and the FEM theory. The rock damage model and the damage-coupling model suited to analyze the whole process of water jet breaking rock were established with continuum damage mechanics and micro damage mechanics. The numerical results show the dynamic response of rock under water jet and the evolvement of hydrodynamic characteristic of jet during rock breaking is close to reality, and indicates that the body of rock damage and breakage under the general continual jet occurs within several milliseconds, the main damage form is tensile damage caused by rock unload and jet impact, and the evolvement of rock damage shows a step-change trend. On the whole, the numerical results can agree with experimental conclusions, which manifest that the analytical method is feasible and can be applied to guide the research and application of jet breaking rock theory.
基金the National Natural Science Foundation of China (No. 51774323)the Natural Science Foundation of Hunan Province, China (No. 2020JJ4704)+1 种基金the Fundamental Research Funds for the Central Universities of Central South University, China (No. 2018zzts216) the financial support from the China Scholarship Councilthe support of the high-performance computer from Compute Canada
文摘Microwave precondition has been highlighted as a promising technology for softening the rock mass prior to rock breakage by machine to reduce drill bit/cutter wear as well as inverse production rate.To numerically explore the effect of numerical parameters on rock static strength simulation,and determine the numerical mechanical parameters of microwave-treated basalts for future drilling and cutting simulations,numerical models of uniaxial compression strength(UCS)and Brazilian tensile strength(BTS)were established with the coupling of smoothed particle hydrodynamics and finite element method(SPH-FEM).To eliminate the large rock strength errors caused by microwave-induced damage,the cohesion and internal friction angle of microwave-treated basalt specimens with the same microwave treatment parameters were calibrated based on a linear Mohr-Coulomb theory.Based on parametric sensitivity analysis of SPH simulation of UCS and BTS,experimental UCS and BTS values were simultaneously captured according to the same set of calibrated cohesion and internal friction angle data,and the UCS modeling results are in good agreement with experimental tests.Furthermore,the effect of microwave irradiation parameter on the basalt mechanical behaviors was evaluated.
