The geometric properties of fracture surfaces significantly influence shear-seepage in rock fractures,introducing complexities to fracture modelling.The present study focuses on the hydro-mechanical behaviours of roug...The geometric properties of fracture surfaces significantly influence shear-seepage in rock fractures,introducing complexities to fracture modelling.The present study focuses on the hydro-mechanical behaviours of rough rock fractures during shear-seepage processes to reveal how dilatancy and fracture asperities affect these phenomena.To achieve this,an improved shear-flow model(SFM)is proposed with the incorporation of dilatancy effect and asperities.In particular,shear dilatancy is accounted for in both the elastic and plastic stages,in contrast to some existing models that only consider it in the elastic stage.Depending on the computation approaches for the peak dilatancy angle,three different versions of the SFM are derived based on Mohr-Coulomb,joint roughness coefficient-joint compressive strength(JRC-JCS),and Grasselli’s theories.Notably,this is a new attempt that utilizes Grasselli’s model in shearseepage analysis.An advanced parameter optimization method is introduced to accurately determine model parameters,addressing the issue of local optima inherent in some conventional methods.Then,model performance is evaluated against existing experimental results.The findings demonstrate that the SFM effectively reproduces the shear-seepage characteristics of rock fracture across a wide range of stress levels.Further sensitivity analysis reveals how dilatancy and asperity affect hydraulic properties.The relation between hydro-mechanical properties(dilatancy displacement and hydraulic conductivity)and asperity parameters is analysed.Several profound understandings of the shear-seepage process are obtained by exploring the phenomenon under various conditions.展开更多
In this study,a high-confining pressure and real-time large-displacement shearing-flow setup was developed.The test setup can be used to analyze the injection pressure conditions that increase the hydro-shearing perme...In this study,a high-confining pressure and real-time large-displacement shearing-flow setup was developed.The test setup can be used to analyze the injection pressure conditions that increase the hydro-shearing permeability and injection-induced seismicity during hot dry rock geothermal extraction.For optimizing injection strategies and improving engineering safety,real-time permeability,deformation,and energy release characteristics of fractured granite samples driven by injected water pressure under different critical sliding conditions were evaluated.The results indicated that:(1)A low injection water pressure induced intermittent small-deformation stick-slip behavior in fractures,and a high injection pressure primarily caused continuous high-speed large-deformation sliding in fractures.The optimal injection water pressure range was defined for enhancing hydraulic shear permeability and preventing large injection-induced earthquakes.(2)Under the same experimental conditions,fracture sliding was deemed as the major factor that enhanced the hydraulic shear-permeability enhancement and the maximum permeability increased by 36.54 and 41.59 times,respectively,in above two slip modes.(3)Based on the real-time transient evolution of water pressure during fracture sliding,the variation coefficients of slip rate,permeability,and water pressure were fitted,and the results were different from those measured under quasi-static conditions.(4)The maximum and minimum shear strength criteria for injection-induced fracture sliding were also determined(μ=0.6665 andμ=0.1645,respectively,μis friction coefficient).Using the 3D(three-dimensional)fracture surface scanning technology,the weakening effect of injection pressure on fracture surface damage characteristics was determined,which provided evidence for the geological markers of fault sliding mode and sliding nature transitions under the fluid influence.展开更多
Both the complex geometrical morphology of rough-walled rock fractures and the nonlinearity of fluid flow contribute to resistance in fluid flow through rock fractures.The interactions of the shear-flow process furthe...Both the complex geometrical morphology of rough-walled rock fractures and the nonlinearity of fluid flow contribute to resistance in fluid flow through rock fractures.The interactions of the shear-flow process further complicate the characterisation of flow behaviours in rock fractures.In this study,an improved friction factor model involving both the effects of viscous and inertial forces is presented based on the Forchheimer equation.The model incorporates two key variables,i.e.Reynolds number and relative roughness,which reflect the effects of flow regimes and fracture roughness,respectively.The changes in geometrical parameters induced by shearing are considered,with the peak asperity height predicted through a correlation with post-peak roughness degradation.The hydraulic aperture during shearing is estimated using a suggested equation that accounts for the mobilised contact area ratio and variable aperture distribution.The parametric sensitivity analysis reveals that shear-induced changes in fracture geometry enhance the flow nonlinearity in rock fractures.The model performs well in predicting the friction factor based on two validation criteria.Then,the proposed friction factor model is incorporated into the three-dimensional distinct element code(3DEC)in the form of the Darcy-Weisbach equation.Coupled with the numerically implemented mechanical model and hydraulic aperture prediction model,numerical simulations of coupled shear-flow processes in single rock fractures are conducted.The simulation outcomes are validated through comparison with the experimental results,showing acceptable agreement and demonstrating that the numerical model is capable of accurately evaluating the hydro-mechanical coupling behaviour during the shearing of rock fractures.展开更多
深部岩石裂隙在剪切过程中形貌不断发生改变,导致裂隙渗流特性极其复杂,进而影响深部岩体工程的稳定性。为探明恒定法向刚度(constant normal stiffness,简称CNS)边界条件下岩石裂隙的剪切渗流特性,基于分形理论构建了不同粗糙度三维自...深部岩石裂隙在剪切过程中形貌不断发生改变,导致裂隙渗流特性极其复杂,进而影响深部岩体工程的稳定性。为探明恒定法向刚度(constant normal stiffness,简称CNS)边界条件下岩石裂隙的剪切渗流特性,基于分形理论构建了不同粗糙度三维自仿射裂隙面,采用考虑裂隙粗糙度退化的剪切数值方法分析了不同CNS边界条件下裂隙岩石剪切过程中几何形貌参数的演变规律。随后利用COMSOL软件对受剪后的裂隙进行渗流计算,研究了法向刚度、剪切位移和分形维数对裂隙非线性渗流特性的影响。结果表明:(1)裂隙的力学开度随着分形维数的增大而增大,但法向刚度的增加会减缓其增长速度;接触率主要受法向刚度控制,并随其增大而增大。(2)裂隙渗流的压力梯度与流量关系能够用Forchheimer定律准确描述,拟合系数A和B随剪切位移的增大呈幂函数减小趋势,随法向刚度的增加而增加,随裂隙分形维数的增加而减小。(3)裂隙的水力开度随分形维数的增加而增加,随法向刚度的增加而减小,并建立了以力学开度和开度标准差为自变量的水力开度模型。(4)裂隙渗流的临界雷诺数随剪切位移的增加先减小后增大,并随分形维数和法向刚度的增加而减小,以裂隙的分形维数、接触率和水力开度模型为基础,建立了CNS条件下剪切裂隙的临界雷诺数计算拟合公式。展开更多
Understanding the mechanical and hydraulic properties of fractured rocks and their coupled processes is of great significance for the exploration,design,construction,operation,and maintenance of many rock engineering ...Understanding the mechanical and hydraulic properties of fractured rocks and their coupled processes is of great significance for the exploration,design,construction,operation,and maintenance of many rock engineering projects such as hydropower development,oil and gas extraction,and underground waste disposal.With the rapid advancement of global and national strategies such as the“Paris Agreement”and the“Belt and Road Initiative”,more and more projects are developed in the complex geological environment with varying geological structures.Shear failure and rock instability are prone to occur in fractured rock masses under the coupled effects of high stress,high pore pressure,and engineering disturbance,which are main sources for engineering disasters such as roof collapse and caving,water and mud inrushes,and induced earthquakes.To solve these problems,extensive research on the coupled shear-flow behavior of fractures has been conducted.However,due to the complex mechanical,hydraulic and geometrical characteristics of single fractures and fracture networks,a large number of outstanding issues related to the impact of the coupled processes on the engineering characteristics of rock masses are still unsolved.The relevant experimental apparatuses and methods remain to be further developed.Therefore,in this review,we analyze and summarize the existing shear-flow experimental apparatuses,classify apparatus configurations,specimen shapes,and testing principles,and compare their advantages and disadvantages.We also summarize the main scientific findings obtained from various experimental apparatuses,aiming to provide a reference for developing new shear-flow experimental apparatuses and conducting related scientific research in the future.展开更多
基金support from the National Natural Science Foundation of China(Grant Nos.51991392 and 42293355).
文摘The geometric properties of fracture surfaces significantly influence shear-seepage in rock fractures,introducing complexities to fracture modelling.The present study focuses on the hydro-mechanical behaviours of rough rock fractures during shear-seepage processes to reveal how dilatancy and fracture asperities affect these phenomena.To achieve this,an improved shear-flow model(SFM)is proposed with the incorporation of dilatancy effect and asperities.In particular,shear dilatancy is accounted for in both the elastic and plastic stages,in contrast to some existing models that only consider it in the elastic stage.Depending on the computation approaches for the peak dilatancy angle,three different versions of the SFM are derived based on Mohr-Coulomb,joint roughness coefficient-joint compressive strength(JRC-JCS),and Grasselli’s theories.Notably,this is a new attempt that utilizes Grasselli’s model in shearseepage analysis.An advanced parameter optimization method is introduced to accurately determine model parameters,addressing the issue of local optima inherent in some conventional methods.Then,model performance is evaluated against existing experimental results.The findings demonstrate that the SFM effectively reproduces the shear-seepage characteristics of rock fracture across a wide range of stress levels.Further sensitivity analysis reveals how dilatancy and asperity affect hydraulic properties.The relation between hydro-mechanical properties(dilatancy displacement and hydraulic conductivity)and asperity parameters is analysed.Several profound understandings of the shear-seepage process are obtained by exploring the phenomenon under various conditions.
基金supported by the National Natural Science Foundation of China (Grant No.52122405)Science and Technology Major Project of Shanxi Province,China (Grant No.202101060301024)Science and Technology Major Project of Xizang Autonomous Region,China (Grant No.XZ202201ZD0004G0204).
文摘In this study,a high-confining pressure and real-time large-displacement shearing-flow setup was developed.The test setup can be used to analyze the injection pressure conditions that increase the hydro-shearing permeability and injection-induced seismicity during hot dry rock geothermal extraction.For optimizing injection strategies and improving engineering safety,real-time permeability,deformation,and energy release characteristics of fractured granite samples driven by injected water pressure under different critical sliding conditions were evaluated.The results indicated that:(1)A low injection water pressure induced intermittent small-deformation stick-slip behavior in fractures,and a high injection pressure primarily caused continuous high-speed large-deformation sliding in fractures.The optimal injection water pressure range was defined for enhancing hydraulic shear permeability and preventing large injection-induced earthquakes.(2)Under the same experimental conditions,fracture sliding was deemed as the major factor that enhanced the hydraulic shear-permeability enhancement and the maximum permeability increased by 36.54 and 41.59 times,respectively,in above two slip modes.(3)Based on the real-time transient evolution of water pressure during fracture sliding,the variation coefficients of slip rate,permeability,and water pressure were fitted,and the results were different from those measured under quasi-static conditions.(4)The maximum and minimum shear strength criteria for injection-induced fracture sliding were also determined(μ=0.6665 andμ=0.1645,respectively,μis friction coefficient).Using the 3D(three-dimensional)fracture surface scanning technology,the weakening effect of injection pressure on fracture surface damage characteristics was determined,which provided evidence for the geological markers of fault sliding mode and sliding nature transitions under the fluid influence.
基金supported by the China Scholarship Council(CSC)(Grant No.202006060033).
文摘Both the complex geometrical morphology of rough-walled rock fractures and the nonlinearity of fluid flow contribute to resistance in fluid flow through rock fractures.The interactions of the shear-flow process further complicate the characterisation of flow behaviours in rock fractures.In this study,an improved friction factor model involving both the effects of viscous and inertial forces is presented based on the Forchheimer equation.The model incorporates two key variables,i.e.Reynolds number and relative roughness,which reflect the effects of flow regimes and fracture roughness,respectively.The changes in geometrical parameters induced by shearing are considered,with the peak asperity height predicted through a correlation with post-peak roughness degradation.The hydraulic aperture during shearing is estimated using a suggested equation that accounts for the mobilised contact area ratio and variable aperture distribution.The parametric sensitivity analysis reveals that shear-induced changes in fracture geometry enhance the flow nonlinearity in rock fractures.The model performs well in predicting the friction factor based on two validation criteria.Then,the proposed friction factor model is incorporated into the three-dimensional distinct element code(3DEC)in the form of the Darcy-Weisbach equation.Coupled with the numerically implemented mechanical model and hydraulic aperture prediction model,numerical simulations of coupled shear-flow processes in single rock fractures are conducted.The simulation outcomes are validated through comparison with the experimental results,showing acceptable agreement and demonstrating that the numerical model is capable of accurately evaluating the hydro-mechanical coupling behaviour during the shearing of rock fractures.
文摘深部岩石裂隙在剪切过程中形貌不断发生改变,导致裂隙渗流特性极其复杂,进而影响深部岩体工程的稳定性。为探明恒定法向刚度(constant normal stiffness,简称CNS)边界条件下岩石裂隙的剪切渗流特性,基于分形理论构建了不同粗糙度三维自仿射裂隙面,采用考虑裂隙粗糙度退化的剪切数值方法分析了不同CNS边界条件下裂隙岩石剪切过程中几何形貌参数的演变规律。随后利用COMSOL软件对受剪后的裂隙进行渗流计算,研究了法向刚度、剪切位移和分形维数对裂隙非线性渗流特性的影响。结果表明:(1)裂隙的力学开度随着分形维数的增大而增大,但法向刚度的增加会减缓其增长速度;接触率主要受法向刚度控制,并随其增大而增大。(2)裂隙渗流的压力梯度与流量关系能够用Forchheimer定律准确描述,拟合系数A和B随剪切位移的增大呈幂函数减小趋势,随法向刚度的增加而增加,随裂隙分形维数的增加而减小。(3)裂隙的水力开度随分形维数的增加而增加,随法向刚度的增加而减小,并建立了以力学开度和开度标准差为自变量的水力开度模型。(4)裂隙渗流的临界雷诺数随剪切位移的增加先减小后增大,并随分形维数和法向刚度的增加而减小,以裂隙的分形维数、接触率和水力开度模型为基础,建立了CNS条件下剪切裂隙的临界雷诺数计算拟合公式。
基金funded by the National Natural Science Foundation of China(Grant Nos.42077252,42011530122)Natural Science Foundation of Shandong Province,China(Grant No.ZR2021QE069).
文摘Understanding the mechanical and hydraulic properties of fractured rocks and their coupled processes is of great significance for the exploration,design,construction,operation,and maintenance of many rock engineering projects such as hydropower development,oil and gas extraction,and underground waste disposal.With the rapid advancement of global and national strategies such as the“Paris Agreement”and the“Belt and Road Initiative”,more and more projects are developed in the complex geological environment with varying geological structures.Shear failure and rock instability are prone to occur in fractured rock masses under the coupled effects of high stress,high pore pressure,and engineering disturbance,which are main sources for engineering disasters such as roof collapse and caving,water and mud inrushes,and induced earthquakes.To solve these problems,extensive research on the coupled shear-flow behavior of fractures has been conducted.However,due to the complex mechanical,hydraulic and geometrical characteristics of single fractures and fracture networks,a large number of outstanding issues related to the impact of the coupled processes on the engineering characteristics of rock masses are still unsolved.The relevant experimental apparatuses and methods remain to be further developed.Therefore,in this review,we analyze and summarize the existing shear-flow experimental apparatuses,classify apparatus configurations,specimen shapes,and testing principles,and compare their advantages and disadvantages.We also summarize the main scientific findings obtained from various experimental apparatuses,aiming to provide a reference for developing new shear-flow experimental apparatuses and conducting related scientific research in the future.
