This paper introduces a new methodology to measure the elastic constants of transversely isotropic rocks from a single uniaxial compression test.We first give the mathematical proof that a uniaxial compression test pr...This paper introduces a new methodology to measure the elastic constants of transversely isotropic rocks from a single uniaxial compression test.We first give the mathematical proof that a uniaxial compression test provides only four independent strain equations.As a result,the exact determination of all five independent elastic constants from only one test is not possible.An approximate determination of the Young’s moduli and the Poisson’s ratios is however practical and efficient when adding the Saint-Venant relation as the fifth equation.Explicit formulae are then developed to calculate both secant and tangent definitions of the five elastic constants from a minimum of four strain measurements.The results of this new methodology applied on three granitic samples demonstrate a significant stress-induced nonlinear behavior,where the tangent moduli increase by a factor of three to four when the rock is loaded up to 20 MPa.The static elastic constants obtained from the uniaxial compression test are also found to be significantly smaller than the dynamic ones obtained from the ultrasonic measurements.展开更多
Electropulse stimulation provides an energy-efficient means of excavating hard rocks through repeated application of high voltage pulses to the rock surface.As such,it has the potential to confer significant advantage...Electropulse stimulation provides an energy-efficient means of excavating hard rocks through repeated application of high voltage pulses to the rock surface.As such,it has the potential to confer significant advantages to mining and drilling operations for mineral and energy resources.Nevertheless,before these benefits can be realized,a better understanding of these processes is required to improve their deployment in the field.In this paper,we employ a recently developed model of the grain-scale processes involved in electropulse stimulation to examine excavation of hard rock under realistic operating conditions.To that end,we investigate the maximum applied voltage within ranges of 120e600 kV,to observe the onset of rock fragmentation.We further study the effect of grain size on rock breakage,by comparing fine(granodiorite)and coarse grained(granite)rocks.Lastly,the pore fluid salinity is investigated,since the electric conductivity of the pore fluid is shown to be a governing factor for the electrical conductivity of the modeled system.This study demonstrates that all investigated factors are crucial to the efficiency of rock fragmentation by electropulsing.展开更多
Fluid injection into rock masses is involved during various subsurface engineering applications.However,elevated fluid pressure,induced by injection,can trigger shear slip(s)of pre-existing natural fractures,resulting...Fluid injection into rock masses is involved during various subsurface engineering applications.However,elevated fluid pressure,induced by injection,can trigger shear slip(s)of pre-existing natural fractures,resulting in changes of the rock mass permeability and thus injectivity.However,the mechanism of slip-induced permeability variation,particularly when subjected to multiple slips,is still not fully understood.In this study,we performed laboratory experiments to investigate the fracture permeability evolution induced by shear slip in both saw-cut and natural fractures with rough surfaces.Our experiments show that compared to saw-cut fractures,natural fractures show much small effective stress when the slips induced by triggering fluid pressures,likely due to the much rougher surface of the natural fractures.For natural fractures,we observed that a critical shear displacement value in the relationship between permeability and accumulative shear displacement:the permeability of natural fractures initially increases,followed by a permeability decrease after the accumulative shear displacement reaches a critical shear displacement value.For the saw-cut fractures,there is no consistent change in the measured permeability versus the accumulative shear displacement,but the first slip event often induces the largest shear displacement and associated permeability changes.The produced gouge material suggests that rock surface damage occurs during multiple slips,although,unfortunately,our experiments did not allow quantitatively continuous monitoring of fracture surface property changes.Thus,we attribute the slip-induced permeability evolution to the interplay between permeability reductions,due to damages of fracture asperities,and permeability enhancements,caused by shear dilation,depending on the scale of the shear displacement.展开更多
基金financially supported by the Swiss Innovation Agency Innosuisseispart of the Swiss Competence Center for Energy Research-Supply of Electricity (SCCER-SoE)+1 种基金the Werner Siemens FoundationETH Zurich for their financial support
文摘This paper introduces a new methodology to measure the elastic constants of transversely isotropic rocks from a single uniaxial compression test.We first give the mathematical proof that a uniaxial compression test provides only four independent strain equations.As a result,the exact determination of all five independent elastic constants from only one test is not possible.An approximate determination of the Young’s moduli and the Poisson’s ratios is however practical and efficient when adding the Saint-Venant relation as the fifth equation.Explicit formulae are then developed to calculate both secant and tangent definitions of the five elastic constants from a minimum of four strain measurements.The results of this new methodology applied on three granitic samples demonstrate a significant stress-induced nonlinear behavior,where the tangent moduli increase by a factor of three to four when the rock is loaded up to 20 MPa.The static elastic constants obtained from the uniaxial compression test are also found to be significantly smaller than the dynamic ones obtained from the ultrasonic measurements.
基金supported by Innosuisse-Swiss Innovation Agency-under grant number 28305.1 PFIW-IWsupport from SwissGeoPower。
文摘Electropulse stimulation provides an energy-efficient means of excavating hard rocks through repeated application of high voltage pulses to the rock surface.As such,it has the potential to confer significant advantages to mining and drilling operations for mineral and energy resources.Nevertheless,before these benefits can be realized,a better understanding of these processes is required to improve their deployment in the field.In this paper,we employ a recently developed model of the grain-scale processes involved in electropulse stimulation to examine excavation of hard rock under realistic operating conditions.To that end,we investigate the maximum applied voltage within ranges of 120e600 kV,to observe the onset of rock fragmentation.We further study the effect of grain size on rock breakage,by comparing fine(granodiorite)and coarse grained(granite)rocks.Lastly,the pore fluid salinity is investigated,since the electric conductivity of the pore fluid is shown to be a governing factor for the electrical conductivity of the modeled system.This study demonstrates that all investigated factors are crucial to the efficiency of rock fragmentation by electropulsing.
基金supported by the National Natural Science Foundation of China(41877239)the Natural Science Foundation of Shandong Province(ZR2022QD014)+2 种基金the Postdoctoral Innovation Project of Shandong Province(SDCX-ZG-202203030)the China Scholarship Council(201806220196)the ZoDrEx project under the grant agreement No.731117.
文摘Fluid injection into rock masses is involved during various subsurface engineering applications.However,elevated fluid pressure,induced by injection,can trigger shear slip(s)of pre-existing natural fractures,resulting in changes of the rock mass permeability and thus injectivity.However,the mechanism of slip-induced permeability variation,particularly when subjected to multiple slips,is still not fully understood.In this study,we performed laboratory experiments to investigate the fracture permeability evolution induced by shear slip in both saw-cut and natural fractures with rough surfaces.Our experiments show that compared to saw-cut fractures,natural fractures show much small effective stress when the slips induced by triggering fluid pressures,likely due to the much rougher surface of the natural fractures.For natural fractures,we observed that a critical shear displacement value in the relationship between permeability and accumulative shear displacement:the permeability of natural fractures initially increases,followed by a permeability decrease after the accumulative shear displacement reaches a critical shear displacement value.For the saw-cut fractures,there is no consistent change in the measured permeability versus the accumulative shear displacement,but the first slip event often induces the largest shear displacement and associated permeability changes.The produced gouge material suggests that rock surface damage occurs during multiple slips,although,unfortunately,our experiments did not allow quantitatively continuous monitoring of fracture surface property changes.Thus,we attribute the slip-induced permeability evolution to the interplay between permeability reductions,due to damages of fracture asperities,and permeability enhancements,caused by shear dilation,depending on the scale of the shear displacement.
