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Nonlinear Flow Properties of Newtonian Fluids through Rough Crossed Fractures

Computer Modeling in Engineering & Sciences 2023年第8期136卷 1427-1440页

作者： Zhenguo liu Shuchen Li richeng liu Changzhou Zheng Geotechnical and Structural Engineering Research Center Shandong UniversityJinan250061China Sinohydro Foundation Engineering Co. Ltd.Tianjin301700China State Key Laboratory for Geomechanics andDeepUnderground Engineering China University of Mining and TechnologyXuzhou221116China

The nonlinear flow properties of Newtonian fluids through crossed fractures are estimated by considering the influences of length,aperture,and surface roughness of fractures.A total of 252 computational runs are performed by creating 36 computational domains,in which the Navier-Stokes equations are *** results show that the nonlinear relationship between flow rate and hydraulic gradient follows Forchheimer’s law–based *** the hydraulic gradient is small(i.e.,10^(−6)),the streamlines are parallel to the fracture walls,indicating a linear streamline *** the hydraulic gradient is large(i.e.,10^(0)),the streamlines are disturbed by a certain number of eddies,indicating a nonlinear streamline *** patterns of eddy distributions depend on the length,aperture,and surface roughness of *** the increment of hydraulic gradient from 10^(−6) to 10^(0),the ratio of flow rate to hydraulic gradient holds constants and then decreases slightly and finally decreases *** fluid flow experiences a linear flow regime,a weakly nonlinear regime,and a strongly nonlinear regime,*** critical hydraulic gradient ranges from 3.27×10^(−5) to 5.82×10^(−2) when fracture length=20–100mmandmechanical aperture=1–*** joint roughness coefficient plays a negligible role in the variations in critical hydraulic gradient compared with fracture length and/or mechanical *** critical hydraulic gradient decreases with increasing mechanical aperture,following power-law *** parameters in the functions are associated with fracture length.

关键词： Crossed fractures surface roughness aperture nonlinear flow critical hydraulic gradient

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Introduction to the Special Issue on Modeling and Simulation of Fluid Flows in Fractured PorousMedia:Current Trends and Prospects

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Computer Modeling in Engineering & Sciences 2021年第2期126卷 437-441页

作者： Qian Yin Yujing Jiang richeng liu State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou221116China Key Laboratory of Mining Disaster Prevention and Control Shandong University of Science and TechnologyQingdao266590China School of Engineering Nagasaki UniversityNagasaki8528521Japan

Understanding the fluid flow mechanisms in fractured porous media plays an important role in many engineering activities,such as nuclear waste disposal,geothermal energy extraction,oil and natural gas production,as well as performance and safety of underground projects including coal mines and *** recent years,many methods including numerical simulation,laboratory experiment and theoretical analysis have been employed to investigate the flowing process and permeability response of rock mass and rock fractures,from kilometer scale to ***,the rocks/coals are in deep underground that is very complex and exists some uncertainties.

关键词： underground rock flowing

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Nonlinear fluid flow through three-dimensional rough fracture networks:Insights from 3D-printing,CT-scanning,and high-resolution numerical simulations

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第5期13卷 1020-1032页

作者： Bo Li Jiafei Wang richeng liu Yujing Jiang Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province Shaoxing UniversityShaoxing312000China State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou221116China School of Engineering Nagasaki UniversityNagasaki852-8521Japan

Nonlinear flow behavior of fluids through three-dimensional(3D)discrete fracture networks(DFNs)considering effects of fracture number,surface roughness and fracture aperture was experimentally and numerically *** physical models of DFNs were 3D-printed and then computed tomography(CT)-scanned to obtain the specific geometry of *** validity of numerically simulating the fluid flow through DFNs was verified via comparison with flow tests on the 3D-printed models.A parametric study was then implemented to establish quantitative relations between the coefficients/parameters in Forchheimer’s law and geometrical *** results showed that the 3D-printing technique can well reproduce the geometry of single fractures with less precision when preparing complex fracture networks,numerical modeling precision of which can be improved via CT-scanning as evidenced by the well fitted results between fluid flow tests and numerical simulations using CT-scanned digital *** in DFNs become increasingly tortuous as the fracture number and roughness increase,resulting in stronger inertial effects and greater curvatures of hydraulic pressure-low rate relations,which can be well characterized by the Forchheimer’s *** critical hydraulic gradient for the onset of nonlinear flow decreases with the increasing aperture,fracture number and roughness,following a power *** increases in fracture aperture and number provide more paths for fluid flow,increasing both the viscous and inertial *** value of the inertial permeability is approximately four orders of magnitude greater than the viscous permeability,following a power function with an exponent a of 3,and a proportional coefficient b mathematically correlated with the geometrical parameters.

关键词： Nonlinear flow 3D-printing CT-scanning Fracture network Permeability Fluid flow test

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Three-dimensional double-rough-walled modeling of fluid flow through self-affine shear fractures

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第1期12卷 41-49页

作者： richeng liu Ming He Na Huang Yujing Jiang Liyuan Yu State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou221116China School of Engineering Nagasaki UniversityNagasaki852-8521Japan School of Petroleum Engineering China University of PetroleumQingdao266580China

This study proposes a double-rough-walled fracture model to represent the natural geometries of rough *** rough surface is generated using a modified successive random additions(SRA)algorithm and the aperture distribution during shearing is calculated using a mechanistic *** shear-flow simulations are performed by directly solving the Navier-Stokes(NS)*** results show that the double-rough-walled fracture model can improve the accuracy of fluid flow simulations by approximately 14.99%-19.77%,compared with the commonly used single-rough-walled fracture *** ratio of flow rate to hydraulic gradient increases by one order of magnitude for fluids in a linear flow regime with increment of shear displacement from 2.2 mm to 2.6 *** solving the NS equations,the inertial effect is taken into account and the significant eddies are simulated and numerically visualized,which are not easy to be captured in conventional *** anisotropy of fluid flow in the linear regime during shearing is robustly enhanced as the shearing advances;however,it is either increased or decreased for fluids in the nonlinear flow regime,depending on the geometry of shear-induced void spaces between the two rough walls of the *** present study provides a method to represent the real geometry of fractures during shearing and to simulate fluid flow by directly solving the NS equations,which can be potentially utilized in many applications such as heat and mass transfer,contaminant transport,and coupled hydro-thermo-mechanical processes within rock fractures/fracture networks.

关键词： Double-rough-walled fracture Navier-Stokes(NS)equations Anisotropy Fractal dimension

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Effect of shear-induced contact area and aperture variations on nonlinear flow behaviors in fractal rock fractures

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Journal of Rock Mechanics and Geotechnical Engineering 2023年第2期15卷 309-322页

作者： Changsheng Wang richeng liu Yujing Jiang Gang Wang Hengjie Luan Shandong Key Laboratory of Civil Engineering Disaster Prevention and Mitigation Shandong University of Science and TechnologyQingdao266590China State Key Laboratory of Mining Disaster Prevention and Control Co-founded By Shandong Province and the Ministry of Science and Technology Shandong University of Science and TechnologyQingdao266590China State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou221116China School of Engineering Nagasaki UniversityNagasaki852-8521Japan

This study experimentally analyzes the nonlinear flow characteristics and channelization of fluid through rough-walled fractures during the shear process using a shear-flow-visualization apparatus.A series of fluid flow and visualization tests is performed on four transparent fracture specimens with various shear displacements of 1 mm,3 mm,5 mm,7 mm and 10 mm under a normal stress of 0.5 *** granite fractures with different roughnesses are selected and quantified using variogram fractal *** obtained results show that the critical Reynolds number tends to increase with increasing shear displacement but decrease with increasing roughness of fracture *** flow paths are more tortuous at the beginning of shear because of the wide distribution of small contact *** the shear displacement continues to increase,preferential flow paths are more distinctly observed due to the decrease in the number of contact spots caused by shear dilation;yet the area of single contacts *** on the experimental results,an empirical mathematical equation is proposed to quantify the critical Reynolds number using the contact area ratio and fractal dimension.

关键词： Fracture Shear displacement Fractal dimension Nonlinear flow Contact area Flow visualization

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Empirical prediction of hydraulic aperture of 2D rough fractures:a systematic numerical study

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Frontiers of Earth Science 2024年第3期18卷 579-597页

作者： Xiaolin WANG Shuchen LI richeng liu Xinjie ZHU Minghui HU State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou 221116China

This study aims to propose an empirical prediction model of hydraulic aperture of 2D rough fractures through numerical simulations by considering the influences of fracture length,average mechanical aperture,minimum mechanical aperture,joint roughness coefficient(JRC)and hydraulic *** generate 600 numerical models using successive random additions(SRA)algorithm and for each model,seven hydraulic gradients spanning from 2.5×10^(-7)to 1 are considered to fully cover both linear and nonlinear flow *** a result,a total of 4200 fluid flow cases are simulated,which can provide sufficient data for the prediction of hydraulic *** results show that as the ratio of average mechanical aperture to fracture length increases from 0.01 to 0.2,the hydraulic aperture increases following logarithm *** the hydraulic gradient increases from 2.5×10^(-7)to 1,the hydraulic aperture decreases following logarithm *** a relatively low hydraulic gradient(i.e.,5×10^(-7))is applied between the inlet and the outlet boundaries,the streamlines are of parallel distribution within the ***,when a relatively large hydraulic gradient(i.e.,0.5)is applied between the inlet and the outlet boundaries,the streamlines are disturbed and a number of eddies are *** hydraulic aperture predicted using the proposed empirical functions agree well with the calculated results and is more reliable than those available in the preceding *** practice,the hydraulic aperture can be calculated as a first-order estimation using the proposed prediction model when the associated parameters are given.

关键词： fluid flow rough fracture surface mechanical aperture hydraulic aperture predictive model

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Anisotropic surface roughness and shear behaviors of rough-walled plaster joints under constant normal load and constant normal stiffness conditions

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Journal of Rock Mechanics and Geotechnical Engineering 2020年第2期12卷 338-352页

作者： richeng liu Sha Lou Xiaojing Li Guansheng Han Yujing Jiang State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou221116China School of Engineering Nagasaki UniversityNagasaki852-8521Japan Department of Hydraulic Engineering Tongji UniversityShanghai200092China School of Civil Engineering Shandong Jianzhu UniversityJinan116024China State Key Laboratory of Mining Disaster Prevention and Control Shandong University of Science and TechnologyQingdao266590China

In this context,we experimentally studied the anisotropic mechanical behaviors of rough-walled plaster joints using a servo-controlled direct shear apparatus under both constant normal load(CNL)and constant normal stiffness(CNS)*** shear-induced variations in the normal displacement,shear stress,normal stress and sheared-off asperity mass are analyzed and correlated with the inclination angle of the critical waviness of joint *** results show that CNS condition gives rise to a smaller normal displacement due to the larger normal stress during shearing,compared with CNL *** CNL conditions,there is one peak shear stress during shearing,whereas there are no peak shear stress for some cases and two peaks for other cases under CNS conditions depending on the geometry of joint *** inclination angle of the critical waviness has been verified to be capable of describing the joint surface roughness and *** joint surface is more significantly damaged under CNS conditions than that under CNL *** increment of the inclination angle of the critical waviness,both the normal displaceme nt and shea red-off asperity mass increase,following power law functions;yet the coefficient of deternination under CNL conditions is larger than that under CNS *** is because the CNS condition significantly decreases the inclination angle of the critical waviness during shearing due to the larger degree of asperity degradation.

关键词： Joint Constant normal load(CNL) Constant normal stiffness(CNS) Shear anisotropy Surface roughness

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Solute Removal Analysis of a Large-Scale Fracture Plane Considering Different Flow Paths and Different Hydraulic Head Differences

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Computer Modeling in Engineering & Sciences 2020年第7期124卷 345-373页

作者： Qian Yin Xiaojing Li Liyuan Yu Ming He richeng liu State Key Laboratory for Geomechanics&Deep Underground Engineering China University of Mining and TechnologyXuzhou221116China School of Engineering Nagasaki UniversityNagasakiJapan School of Civil Engineering Shandong Jianzhu UniversityJinan116024China

An experimental and numerical study was carried out to investigate the solute removal process through a large-scale fracture plane considering different flow paths and hydraulic head *** visualization techniques were utilized in the experiment to capture the removal process images,which were then transferred to binary *** variations in dimensionless concentration,which is defined as saturation of solute phase,were *** increasing hydraulic head difference,the speed of solute removal increases and the dimensionless concentration *** flow paths result in different solute distribution patterns and different mechanisms for solute removal such as advection and diffusion,thus the curves of dimensionless concentration versus time are *** dimensionless concentration over time decreases from approximately 1,which is smaller than 1 due to the existence of bubbles,to approximately 0,which is larger than 0 because the folds of the background are dealt as“solute”.A significant longer time is needed to achieve a certain fixed dimensionless concentration for a smaller hydraulic head *** the finite element software COMSOL multiphysics,the solute removal process,flow velocity fields,flow streamlines,as well as the hydraulic pressure fields were analyzed,which shows a good consistency with the experimental *** practical engineering,when the solute pollutes the underground environment,the removal ability can be more significantly enforced by immediately applying a larger hydraulic head difference along a longer distance between the inlet and outlet boundaries.

关键词： Solute removal rock fracture visualization hydraulic head difference

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Estimates of strength and cracking behaviors of pre-flawed granite specimens treated by chemical corrosion under triaxial compression tests

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Frontiers of Earth Science 2022年第2期16卷 411-434页

作者： Zhicong LI richeng liu Shuchen LI Hongwen JING Xiaozhao LI Liyuan YU State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou 221116China

Four types of granite specimens were prepared and treated by chemical corrosion for 5 and 30 days,which were then used to carry out triaxial compression tests under different confining pressuresσ_(3).Type A is the intact sample with no preexisting *** B and C are the samples containing two relatively low-dip flaws and two relatively high-dip flaws,*** D is the sample including both relatively low-dip and relatively high-dip *** influences of pH value of chemical solutions,flaw distribution,corrosion time andσ_(3) on triaxial stress-strain curves and ultimate failure modes are analyzed and *** results show that the pH value of the chemical solution,corrosion time and the arrangement of preexisting flaws play crucial roles in the cracking behaviors of granite *** A specimens have the largest peak axial deviatoric stress,followed by Type C,Type D,and Type B specimens,*** is because the decrease in the inclination of preexisting flaws induces the weakening effect due to the decrease in the shadow area along the compaction *** aσ_(3) of 5 MPa,the peak axial deviatoric stress drops by approximately 40.89%,29.08%,4.08%,and 23.53%for pH=2,4,7,and 12,*** intact granite(Type A)specimens,the ultimate failure mode displays a typical shear *** connection of two secondary cracks initiated at the tips of preexisting cracks is always the ultimate failure and crack coalescence mode for Type B *** ultimate failure and crack coalescence mode of Types C and D specimens are significantly affected by pH value of the chemical solution,corrosion time andσ_(3),which is different from those of Types A and B specimens due to the differences in flow distributions.

关键词： granites preexisting flaws chemical corrosion triaxial compression strength cracking behavior

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Cyclic shear behavior of en-echelon joints under constant normal stiffness conditions

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Journal of Rock Mechanics and Geotechnical Engineering 2024年第9期16卷 3419-3436页

作者： Bin Wang Yujing Jiang Qiangyong Zhang Hongbin Chen richeng liu Yuanchao Zhang Graduate School of Engineering Nagasaki UniversityNagasaki852-8521Japan Research Center of Geotechnical and Structural Engineering Shandong UniversityJi’nan250061China State Key Laboratory for Geomechanics and Deep Underground Engineering China University of Mining and TechnologyXuzhou221116China College of Civil Engineering Fuzhou UniversityFuzhou350108China

To reveal the mechanism of shear failure of en-echelon joints under cyclic loading,such as during earthquakes,we conducted a series of cyclic shear tests of en-echelon joints under constant normal stiffness(CNS)*** analyzed the evolution of shear stress,normal stress,stress path,dilatancy characteristics,and friction coefficient and revealed the failure mechanisms of en-echelon joints at different *** results show that the cyclic shear behavior of the en-echelon joints is closely related to the joint angle,with the shear strength at a positive angle exceeding that at a negative angle during shear *** the number of cycles increases,the shear strength decreases rapidly,and the difference between the varying angles gradually *** occurs in the early shear cycles(1 and 2),while contraction is the main feature in later cycles(310).The friction coefficient decreases with the number of cycles and exhibits a more significant sensitivity to joint angles than shear *** joint angle determines the asperities on the rupture surfaces and the block size,and thus determines the subsequent shear failure mode(block crushing and asperity degradation).At positive angles,block size is more greater and asperities on the rupture surface are smaller than at nonpositive ***,the cyclic shear behavior is controlled by block crushing at positive angles and asperity degradation at negative angles.

关键词： En-echelon joint Cyclic shear tests Shear stress Normal displacement Constant normal stiffness(CNS)

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