High-voltage electric pulse(HVEP)rock fragmentation has demonstrated substantial potential for sustainable fracturing of hard rocks owing to its energy efficiency.The transient nature and highly disruptive characteris...High-voltage electric pulse(HVEP)rock fragmentation has demonstrated substantial potential for sustainable fracturing of hard rocks owing to its energy efficiency.The transient nature and highly disruptive characteristics of its physical fracturing process render experimental investigation of the underlying rock-breaking mechanisms challenging.However,existing numerical studies lack comprehensive models that precisely link electrical breakdown phenomena with mechanical disintegration processes.This study combines COMSOL electrical breakdown simulations with four-dimension lattice spring model(4D-LSM)mechanical analysis to establish a coupled HVEP rock fragmentation model.The core concept of the model construction is to import the temperature field of the plasma channel obtained from the electrical breakdown into the mechanical solver to realize the precise connection between the two stages.The validated numerical model elucidates the full process of HVEP-induced fragmentation under varying electrical parameters.Furthermore,the effects of confining pressure and mineral grain size on fragmentation behavior have been investigated.Finally,parametric simulations across 25 electrical parameter combinations demonstrate the critical role of electrode spacing optimization in achieving energy-efficient rock fragmentation.These findings provide a predictive tool for designing efficient HVEP systems in deep resource extraction and mineral processing engineering.展开更多
To analyze and predict the mechanical behaviors of deep hard rocks,some key issues concerning rock fracturing mechanics for deep hard rock excavations are discussed.First,a series of apparatuses and methods have been ...To analyze and predict the mechanical behaviors of deep hard rocks,some key issues concerning rock fracturing mechanics for deep hard rock excavations are discussed.First,a series of apparatuses and methods have been developed to test the mechanical properties and fracturing behaviors of hard rocks under high true triaxial stress paths.Evolution mechanisms of stress-induced disasters in deep hard rock excavations,such as spalling,deep cracking,massive roof collapse,large deformation and rockbursts,have been recognized.The analytical theory for the fracturing process of hard rock masses,including the three-dimensional failure criterion,stress-induced mechanical model,fracturing degree index,energy release index and numerical method,has been established.The cracking-restraint method is developed for mitigating or controlling rock spalling,deep cracking and massive collapse of deep hard rocks.An energy-controlled method is also proposed for the prevention of rockbursts.Finally,two typical cases are used to illustrate the application of the proposed methodology in the Baihetan caverns and Bayu tunnels of China.展开更多
Rock fracturing is often accompanied by electromagnetic phenomenon.As a vector field,in addition to the intensity that is widely concerned,the generated electromagnetic field also has obvious direction-ality.To this e...Rock fracturing is often accompanied by electromagnetic phenomenon.As a vector field,in addition to the intensity that is widely concerned,the generated electromagnetic field also has obvious direction-ality.To this end,a set of electromagnetic antennas capable of simultaneous three-axis measurement is used to monitor the electromagnetic vector field generated from rock fracturing based on Brazilian tests.The signal amplitude on each axis can represent the magnitude of actual magnetic flux density component on the three axes.The intensity and directional characteristics of electromagnetic signals received at different positions are studied using vector synthesis.The directionality of electromagnetic radiation measured using a three-axis electromagnetic antenna shows that the direction of the magnetic flux intensity generated by rock fracturing tends to be parallel to the crack surface,and the measured signal intensity is greater in a direction closer to the crack surface.展开更多
The influence of rock mechanical properties on the electromagnetic radiation(EMR)mechanism of rock fracturing is an important research topic in solid mechanics and earthquake prediction.In this study,an EMR model of r...The influence of rock mechanical properties on the electromagnetic radiation(EMR)mechanism of rock fracturing is an important research topic in solid mechanics and earthquake prediction.In this study,an EMR model of rock fracturing considering the fracture factor,elastic modulus,Poisson’s ratio,radiation distance and crack length is derived based on the Hertz oscillator array assumption.An experimental system,including an electromagnetic shielding module,an EMR signal induction and transmission module,a signal recording module and a loading module,is developed to understand the EMR characteristics of four different rocks.The validity of the EMR theoretical model is verified and the relationships between the rock cracking morphology and the EMR waveform,amplitude and frequency are revealed.It is found that rock mechanical properties have obvious influences on the EMR waveform,amplitude and frequency during rock fracturing.This study provides a better understanding on the EMR mechanism of rock fracturing and can help to improve the accuracy of rock disaster prediction based on EMR.展开更多
The seismic failure of jointed rock slopes is essentially a problem of dynamic fracturing and instability of discontinuous rock masses.In this study,seismic failures of anti-dip jointed rock slopes are numerically inv...The seismic failure of jointed rock slopes is essentially a problem of dynamic fracturing and instability of discontinuous rock masses.In this study,seismic failures of anti-dip jointed rock slopes are numerically investigated by the sub-block splitting discontinuous deformation analysis(DDA)method.Firstly,diametrically compressive rock discs with a central pre-existing crack of different inclinations are simulated to verify the effectiveness of the sub-block splitting DDA method for rock fracturing simulations.Thereafter,the fracturing failure and instability process of five anti-dip jointed rock slopes with different configurations under the Wenchuan earthquake waves of different amplitudes are simulated.Results indicate that with larger excavation area of the slope and larger amplitude of the seismic loads,and under specific horizontal relative direction of the seismic wave to the slope(SSHRD),the slope stability will be dramatically reduced,and the failure mode will also be changed upon a basic mode of toppling.The surface and elevation amplification effects of the slope under seismic loads are successfully reproduced as well by the simulations.This work reveals the seismic failure process and mechanism of anti-dip jointed rock slopes,and could provide theoretical reference to the disaster prediction of anti-dip jointed rock slopes under earthquakes.展开更多
This study introduces a test system for microwave-induced fracturing of hard rocks under true triaxial stress.The test system comprises a true triaxial stress loading system,an open-ended microwaveinduced fracturing s...This study introduces a test system for microwave-induced fracturing of hard rocks under true triaxial stress.The test system comprises a true triaxial stress loading system,an open-ended microwaveinduced fracturing system,a data acquisition system,an acoustic emission(AE)monitoring system,and an auxiliary specimen loading system.Microwave-induced surface and borehole fracturing tests under true triaxial stress were fulfilled for the first time,which overcomes the problem of microwave leakage in the coupling loading of true triaxial stress and microwave.By developing the dynamic monitoring system,the thermal response and fracture evolution were obtained during microwave irradiation.The monitoring system includes the infrared thermometry technique for monitoring rock surface temperature,the distributed optic fiber sensing technique for monitoring temperature in borehole in rock,the AE technique and two-dimensional digital speckle correlation technique for monitoring the evolution of thermal damage and the rock fracturing process.To validate the advantages of the test system and investigate the characteristics of microwave-induced fracturing of hard rocks,the study demonstrates the experimental methods and results for microwave-induced surface and borehole fracturing under true triaxial stress.The results show that thermal cracking presented intermittent characteristics(calm eactiveecalm)during microwave-induced surface and borehole fracturing of basalt.In addition,true triaxial stress can inhibit the development and distribution of thermal cracks during microwave-induced surface fracturing.When microwave-induced borehole fracturing occurs,it promotes the distribution of thermal cracks in rock,but inhibits the width of cracks.The results also prove the reliability of the test system.展开更多
The goal of this review paper is to provide a summary of selected discrete element and hybrid finitediscrete element modeling techniques that have emerged in the field of rock mechanics as simulation tools for fractur...The goal of this review paper is to provide a summary of selected discrete element and hybrid finitediscrete element modeling techniques that have emerged in the field of rock mechanics as simulation tools for fracturing processes in rocks and rock masses. The fundamental principles of each computer code are illustrated with particular emphasis on the approach specifically adopted to simulate fracture nucleation and propagation and to account for the presence of rock mass discontinuities. This description is accompanied by a brief review of application studies focusing on laboratory-scale models of rock failure processes and on the simulation of damage development around underground excavations.展开更多
To elucidate the dynamic characteristics of in-situ methane deflagration in coalbed methane wellbores and its mechanisms for fracturing coal rock,this study first developed a simulation experimental system specificall...To elucidate the dynamic characteristics of in-situ methane deflagration in coalbed methane wellbores and its mechanisms for fracturing coal rock,this study first developed a simulation experimental system specifically designed for methane in-situ deflagration fracturing.This experimental system,which is capable of withstanding pressures up to 150 MPa and meanwhile applying axial and confining pressures of up to 50 MPa to rock cores,enables the coupled simulation on methane deflagration and rock core fracturing processes.With the aid of this experimental system,physical simulation experiments on in-situ methane deflagration fracturing were conducted,and the following findings were obtained.Methane deflagration loads in enclosed wellbores exhibit characteristics of multi-level pulsed oscillation.With the rise of initial gas pressure,the peak deflagration load increases approximately linearly,with the pressure amplification factor spanning from 23.14 to 31.10,and its peak loading rate grows exponentially.Accordingly,the fracture volume and fracture porosity augment.To be specific,when the initial gas pressure rises from 0.6 to 2.4 MPa,the fracture volume and fracture porosity augment by factors of 14.0 and 8.73,respectively.The fractal dimension of spatial distribution of fractures also increases with the rise of deflagration load,indicating that a higher deflagration load conduces to the development of a larger and more complex fracture network.Methane deflagration fracturing is characterized as a composite fracture mode that involves the impact of strong stress waves and the driving force of high-pressure fluids.The primary factors influencing damage to coal-rock include the high-stress impact in the initial stage of deflagration,the fluid pressure driving effect in the middle stage,and the thermal shock resulting from high temperatures in the later stage.展开更多
This study proposed a repeated adjustable mixture injection strategy(RAM)based microbial induced carbonate precipitation(MICP)for efficient mitigation of rock fracture leakage.Granite fractures with small apertures we...This study proposed a repeated adjustable mixture injection strategy(RAM)based microbial induced carbonate precipitation(MICP)for efficient mitigation of rock fracture leakage.Granite fractures with small apertures were investigated,and bio-sealing experiments were conducted using five different cementation solution(CS)concentrations(0.25−2 M).The results showed that the RAM-based bio-sealing method can seal and bond the small aperture rock fractures with high efficiency and uniform precipitation by adjusting the CS concentration.The RAM-based bio-sealing mechanism is attributed to the following four stages:(1)fixation of bacterial flocs onto the fracture surfaces,(2)precipitation of CaCO3 onto the fracture surfaces,(3)growth of pre-precipitated CaCO3 and adhesion of new-suspended CaCO3,and(4)bridging and clogging processes.The optimal CS concentration of 1 M resulted in a fracture filling rate up to 85%,a transmissivity reduction of 4 orders of magnitude,and a shear strength ranging from 512 kPa to 688 kPa.The bio-sealing effect was found to be influenced by the CS concentration on bacterial attachment,calcium carbonate yield and calcium carbonate bulk density.The CS concentration of 1 M promoted bacterial attachment,and increased calcium carbonate yield as well as calcium carbonate bulk density,while concentrations above 1 M had the opposite effect.The bulk density of calcium carbonate played a crucial role in the sealing and bonding performance of bio-sealed fractures,particularly at comparable filling ratios and bridging areas.The bulk density was regulated by the size of calcium carbonate crystals and was determined by Ca2+concentration in the CS.This study provides valuable insights into the RAM-based bio-sealing method,highlighting its potential for efficient rock fracture leakage mitigation through precise control of CS concentration and understanding the underlying mechanisms.展开更多
Grouting has been the most effective approach to mitigate water inrush disasters in underground engineering due to its ability to plug groundwater and enhance rock strength.Nevertheless,there is a lack of potent numer...Grouting has been the most effective approach to mitigate water inrush disasters in underground engineering due to its ability to plug groundwater and enhance rock strength.Nevertheless,there is a lack of potent numerical tools for assessing the grouting effectiveness in water-rich fractured strata.In this study,the hydro-mechanical coupled discontinuous deformation analysis(HM-DDA)is inaugurally extended to simulate the grouting process in a water-rich discrete fracture network(DFN),including the slurry migration,fracture dilation,water plugging in a seepage field,and joint reinforcement after coagulation.To validate the capabilities of the developed method,several numerical examples are conducted incorporating the Newtonian fluid and Bingham slurry.The simulation results closely align with the analytical solutions.Additionally,a set of compression tests is conducted on the fresh and grouted rock specimens to verify the reinforcement method and calibrate the rational properties of reinforced joints.An engineering-scale model based on a real water inrush case of the Yonglian tunnel in a water-rich fractured zone has been established.The model demonstrates the effectiveness of grouting reinforcement in mitigating water inrush disaster.The results indicate that increased grouting pressure greatly affects the regulation of water outflow from the tunnel face and the prevention of rock detachment face after excavation.展开更多
The overall heat transfer coefficient(OHTC)of rock fractures is a fundamental parameter for characterizing the heat transfer behavior of rock fractures in hot dry rock(HDR)geothermal mining.Although a number of practi...The overall heat transfer coefficient(OHTC)of rock fractures is a fundamental parameter for characterizing the heat transfer behavior of rock fractures in hot dry rock(HDR)geothermal mining.Although a number of practical formulae for heat transfer coefficients have been developed in the literature,there is still no widely accepted analytical solution.This paper constructs highly accurate analytical solutions for the temperatures of the inner fracture wall and the fluid.Then they are employed to develop new definition-based formulae(formula A and its simplification formula B)of the OHTC,which are well validated by the experimental and numerical simulation results.An empirical correlation formula of heat transfer coefficient is proposed based on the definition-based formulae which can be directly used in the numerical simulations of heat transfer in rock fractures.A site-scale application example of numerical simulation also demonstrates the effectiveness of the empirical correlation formula.展开更多
Coupled thermo-hydro-mechanical(THM)processes in fractured rock are playing a crucial role in geoscience and geoengineering applications.Diverse and conceptually distinct approaches have emerged over the past decades ...Coupled thermo-hydro-mechanical(THM)processes in fractured rock are playing a crucial role in geoscience and geoengineering applications.Diverse and conceptually distinct approaches have emerged over the past decades in both continuum and discontinuum perspectives leading to significant progress in their comprehending and modeling.This review paper offers an integrated perspective on existing modeling methodologies providing guidance for model selection based on the initial and boundary conditions.By comparing various models,one can better assess the uncertainties in predictions,particularly those related to the conceptual models.The review explores how these methodologies have significantlyenhanced the fundamental understanding of how fractures respond to fluid injection and production,and improved predictive capabilities pertaining to coupled processes within fractured systems.It emphasizes the importance of utilizing advanced computational technologies and thoroughly considering fundamental theories and principles established through past experimental evidence and practical experience.The selection and calibration of model parameters should be based on typical ranges and applied to the specificconditions of applications.The challenges arising from inherent heterogeneity and uncertainties,nonlinear THM coupled processes,scale dependence,and computational limitations in representing fieldscale fractures are discussed.Realizing potential advances on computational capacity calls for methodical conceptualization,mathematical modeling,selection of numerical solution strategies,implementation,and calibration to foster simulation outcomes that intricately reflectthe nuanced complexities of geological phenomena.Future research efforts should focus on innovative approaches to tackle the hurdles and advance the state-of-the-art in this critical fieldof study.展开更多
The fractured rock mass inherently exhibits uncertainty due to the presence of pre-existing discontinuities.In this study,a particle-based model incorporating the discrete fracture network(DFN)to elucidate the dynamic...The fractured rock mass inherently exhibits uncertainty due to the presence of pre-existing discontinuities.In this study,a particle-based model incorporating the discrete fracture network(DFN)to elucidate the dynamic tensile responses and asso-ciated uncertainty of rock mass.At first,the particle-based model was used synthesize the intact rock and split Hopkinson pressure bar(SHPB)system,while the fractures were represented using the smooth fracture model(SJM).Subsequently,the samples of the fractured rock mass with varying joint geometrical configurations were conducted the dynamic tensile test using the numerical SHPB system.The simulated results demonstrate a gradual decrease in dynamic tensile strength(TS)with increasing fracture intensity and fracture length,which can be effectively described by nonlinear exponential func-tions.Additionally,the fracture orientation significantly influences the dynamic TS,however,the anisotropic characteristics gradually diminish as the deviation angle approaches 90°.Furthermore,as fracture intensity and fracture length increase,the dynamic TS variability also rises steadily.However,no noticeable pattern is seen when considering cases with varying fracture orientations.When subjected to SHPB loading,the fractured rock mass primarily exhibits a combined tensile-shear failure mode,contrasting with the pure tensile failure mode exhibited by the intact rock.These findings contribute signifi-cantly to comprehending the dynamic tensile responses of the fractured rock mass and can further enhance the stability analysis of in-situ rock engineering.展开更多
Wellbore breakout is one of the critical issues in drilling due to the fact that the related problems result in additional costs and impact the drilling scheme severely.However,the majority of such wellbore breakout a...Wellbore breakout is one of the critical issues in drilling due to the fact that the related problems result in additional costs and impact the drilling scheme severely.However,the majority of such wellbore breakout analyses were based on continuum mechanics.In addition to failure in intact rocks,wellbore breakouts can also be initiated along natural discontinuities,e.g.weak planes and fractures.Furthermore,the conventional models in wellbore breakouts with uniform distribution fractures could not reflect the real drilling situation.This paper presents a fully coupled hydro-mechanical model of the SB-X well in the Tarim Basin,China for evaluating wellbore breakouts in heavily fractured rocks under anisotropic stress states using the distinct element method(DEM)and the discrete fracture network(DFN).The developed model was validated against caliper log measurement,and its stability study was carried out by stress and displacement analyses.A parametric study was performed to investigate the effects of the characteristics of fracture distribution(orientation and length)on borehole stability by sensitivity studies.Simulation results demonstrate that the increase of the standard deviation of orientation when the fracture direction aligns parallel or perpendicular to the principal stress direction aggravates borehole instability.Moreover,an elevation in the average fracture length causes the borehole failure to change from the direction of the minimum in-situ horizontal principal stress(i.e.the direction of wellbore breakouts)towards alternative directions,ultimately leading to the whole wellbore failure.These findings provide theoretical insights for predicting wellbore breakouts in heavily fractured rocks.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
Non-Darcian flow in rock fractures exhibits significant anisotropic characteristics,which can be affected by mechanical processes,such as cyclic shearing.Understanding the evolution of anisotropic nonDarcian flow is c...Non-Darcian flow in rock fractures exhibits significant anisotropic characteristics,which can be affected by mechanical processes,such as cyclic shearing.Understanding the evolution of anisotropic nonDarcian flow is crucial for characterizing groundwater flow and mass/heat transport in fractured rock masses.In this study,we conducted experiments on non-Darcian flow in single rough fractures under cyclic shearing conditions,aiming to analyze the anisotropic evolution of inertial permeability and viscous permeability.We established quantitative characterization models for the two types of permeability.First,we conducted cyclic shearing experiments on four sets of 24 rough rock fractures,investigating their shear characteristics.Then,we performed 480 non-Darcian flow experiments to analyze the anisotropic evolution of viscous permeability and inertial permeability of these rock fractures.The results showed that viscous permeability exhibited significant differences only in the orthogonal direction,while inertial permeability exhibited differences in both orthogonal and opposite directions.With increase in the shear cycles,the differences in the orthogonal direction gradually increased,while those in opposite direction gradually decreased.Finally,we established characterization equations for the two permeabilities based on the proposed directional geometric parameters and validated the performance of these equations with experimental data.These findings are useful for the quantitative characterization of the evolution of non-Darcian flow in fractures under dynamic loading conditions.展开更多
The shear characteristics of bolted rock joints are crucial for the stability of tunneling and mining,particularly in deep underground engineering,where rock bolt materials are exposed to high stress,water pressure,an...The shear characteristics of bolted rock joints are crucial for the stability of tunneling and mining,particularly in deep underground engineering,where rock bolt materials are exposed to high stress,water pressure,and engineering disturbance.However,due to the complex interaction between bolted rock joints and various geological contexts,many challenges and unsolved problems arise.Therefore,more investigation is needed to understand the shear performance of bolted joints in the field of deep underground engineering.This study presents a comprehensive review of research findings on the responses of bolted joints subjected to shearing under different conditions.As is revealed,the average shear strength of bolted rock joints increases linearly with the normal stress and increases with the compressive strength of rock until it reaches a stable value.The joint roughness coefficient(JRC)affects the contact area,friction force,shear strength,bending angle,and axial force of bolted rock joints.A mathematical function is proposed to model the relationship between JRC,normal load,and shear strength.The normal stress level also influences the deformation model,load-carrying capacity,and energy absorption ratio of bolts within bolted rock joints,and can be effectively characterized by a two-phase exponential equation.Additionally,the angle of the bolts affects the ratio of tensile and shear strength of the bolts,as well as the mechanical behavior of both bolted rock joints and surrounding rock,which favors smaller angles.This comprehensive review of experimental data on the shear behavior of bolted rock joints offers valuable theoretical insights for the development of advanced shear devices and further pertinent investigations.展开更多
To evaluate the thermal behavior of tunnels,an equivalent thermal conductivity(ETC)model for the fractured rock masses surrounding tunnels was proposed,based on the series-parallel theory,which incorporates the heat t...To evaluate the thermal behavior of tunnels,an equivalent thermal conductivity(ETC)model for the fractured rock masses surrounding tunnels was proposed,based on the series-parallel theory,which incorporates the heat transfer characteristics of the surrounding rock.A thermal probe test(TPT)was subsequently conducted at the Dajian Mountain Tunnel(China),and the heat transfer model of the thermal probe was developed and calibrated based on the TPT results.The ETCs of different test areas in the borehole were calculated based on the fracture parameters(dip direction,dip angle,opening,trace length),obtained via a digital borehole photography test.Finally,the new ETC model,the volumeaveraged model,and the non-fracture model were compared for accuracy in heat transfer calculation.The results demonstrate that(1)the error of heat transfer calculation error was reduced by 17.2%e69.2%using the new ETC model.(2)For the ETCs of different thermal response test areas,the minimum and maximum values were 2.15 W/(m K)and 3.7 W/(m K),respectively,with the fracture effect causing up to a 41.2%reduction in thermal conductivity.(3)For the ETC of the borehole,the ETC value was 2.53 W/(m K),with the fracture effect leading to a 31.6%reduction in thermal conductivity.The effect of fractures on the thermal conductivity of rock mass could not be ignored.This ETC model addresses the challenge of determining the ETC for the heterogeneous surrounding rock of tunnels and provides a more accurate representation of the in situ thermal behavior of tunnels.展开更多
The shear behavior of fractured rock masses critically infuences engineering stability,particularly in slope engineering.Overcoming limitations of conventional preparation methods,this study utilizes sand-powder 3D pr...The shear behavior of fractured rock masses critically infuences engineering stability,particularly in slope engineering.Overcoming limitations of conventional preparation methods,this study utilizes sand-powder 3D printing to fabricate rocklike specimens with controlled internal fractures.Direct shear tests systematically investigate fracture radius and number efects on strength evolution under constant density,with quantitative analysis revealing their diferential contributions.The results show that:(1)The failure of sand-powder 3D-printed fractured rock-like specimens exhibits brittle characteristics.The shear stress-shear displacement relationship can be divided into fve stages:compaction,elasticity,unstable development,peak,and post-peak.Crack initiation and propagation primarily occur from the late elastic stage to the peak stage.(2)An increase in fracture radius signifcantly reduces pre-peak shear stifness,resulting in a smoother curve progression,while changes in fracture number have minimal impact on the stage-specifc characteristics of the shear curve.(3)Shear strength decreases exponentially with increasing fracture radius,whereas an increase in fracture number leads to a linear reduction in shear strength.Moreover,the weakening efect of fracture number on shear strength becomes more pronounced with larger fracture radius.(4)Quantitative analysis shows that the infuence of fracture radius on shear strength is 2.4 times greater than that of fracture number.This study broadens the understanding of the shear behaviors of fractured rock masses and reveals the key infuence mechanism of fracture density on rock mass deformation and failure,and provides theoretical guidance for slope stability analysis and rock mass engineering design.展开更多
A complete rock failure process usually involves opening/sliding of preexisting discontinuities as well as frac- turing in intact rock bridges to form persistent failure sur- faces and subsequent motions of the genera...A complete rock failure process usually involves opening/sliding of preexisting discontinuities as well as frac- turing in intact rock bridges to form persistent failure sur- faces and subsequent motions of the generated rock blocks. The recently developed numerical manifold method （NMM） has potential for modelling such a complete failure process. However, the NMM suffers one limitation, i.e., unexpected material domain area change occurs in rotation modelling. This problem can not be easily solved because the rigid body rotation is not represented explicitly in the NMM. The discontinuous deformation analysis （DDA） is specially de- veloped for modelling discrete block systems. The rotation- induced material area change in the DDA modelling can be avoided conveniently because the rigid body rotation is represented in an explicit form. In this paper, a transition technique is proposed and implemented to convert a NMMmodelling to a DDA modelling so as to simulate a complete rock failure process entirely by means of the two methods, in which the NMM is adopted to model the early fracturing as well as the transition from continua to discontinua, while the DDA is adopted to model the subsequent motion of the generated rock blocks. Such a numerical approach also im- proves the simulation efficiency greatly as compared with a complete NMM modelling approach. The fracturing of a rock slab with pre-existing non-persistent joints located on a slope crest and the induced rockfall process are simulated. The validity of the modelling transition from the NMM to the DDA is verified and the applicability of the proposed nu- merical approach is investigated.展开更多
基金financial support from the National Natural Science Foundation of China(Nos.52209144 and 12472405).
文摘High-voltage electric pulse(HVEP)rock fragmentation has demonstrated substantial potential for sustainable fracturing of hard rocks owing to its energy efficiency.The transient nature and highly disruptive characteristics of its physical fracturing process render experimental investigation of the underlying rock-breaking mechanisms challenging.However,existing numerical studies lack comprehensive models that precisely link electrical breakdown phenomena with mechanical disintegration processes.This study combines COMSOL electrical breakdown simulations with four-dimension lattice spring model(4D-LSM)mechanical analysis to establish a coupled HVEP rock fragmentation model.The core concept of the model construction is to import the temperature field of the plasma channel obtained from the electrical breakdown into the mechanical solver to realize the precise connection between the two stages.The validated numerical model elucidates the full process of HVEP-induced fragmentation under varying electrical parameters.Furthermore,the effects of confining pressure and mineral grain size on fragmentation behavior have been investigated.Finally,parametric simulations across 25 electrical parameter combinations demonstrate the critical role of electrode spacing optimization in achieving energy-efficient rock fragmentation.These findings provide a predictive tool for designing efficient HVEP systems in deep resource extraction and mineral processing engineering.
基金financial support from the National Natural Science Foundation of China(Grant Nos.51839003 and 41827806)Liaoning Revitalization Talents Program of China(Grant No.XLYCYSZX1902)。
文摘To analyze and predict the mechanical behaviors of deep hard rocks,some key issues concerning rock fracturing mechanics for deep hard rock excavations are discussed.First,a series of apparatuses and methods have been developed to test the mechanical properties and fracturing behaviors of hard rocks under high true triaxial stress paths.Evolution mechanisms of stress-induced disasters in deep hard rock excavations,such as spalling,deep cracking,massive roof collapse,large deformation and rockbursts,have been recognized.The analytical theory for the fracturing process of hard rock masses,including the three-dimensional failure criterion,stress-induced mechanical model,fracturing degree index,energy release index and numerical method,has been established.The cracking-restraint method is developed for mitigating or controlling rock spalling,deep cracking and massive collapse of deep hard rocks.An energy-controlled method is also proposed for the prevention of rockbursts.Finally,two typical cases are used to illustrate the application of the proposed methodology in the Baihetan caverns and Bayu tunnels of China.
基金This work was supported by the National Natural Science Foundation of China(Grant No.51904019)Key Scientific Research Projects Plan of Henan Higher Education Institution(Grant No.21A620001)Fundamental Research Funds for the Central Universities(Grant No.FRF-IDRY-20-006).
文摘Rock fracturing is often accompanied by electromagnetic phenomenon.As a vector field,in addition to the intensity that is widely concerned,the generated electromagnetic field also has obvious direction-ality.To this end,a set of electromagnetic antennas capable of simultaneous three-axis measurement is used to monitor the electromagnetic vector field generated from rock fracturing based on Brazilian tests.The signal amplitude on each axis can represent the magnitude of actual magnetic flux density component on the three axes.The intensity and directional characteristics of electromagnetic signals received at different positions are studied using vector synthesis.The directionality of electromagnetic radiation measured using a three-axis electromagnetic antenna shows that the direction of the magnetic flux intensity generated by rock fracturing tends to be parallel to the crack surface,and the measured signal intensity is greater in a direction closer to the crack surface.
基金supported by the National Natural Science Foundation of China(Grant Nos.51979146 and 11272178)。
文摘The influence of rock mechanical properties on the electromagnetic radiation(EMR)mechanism of rock fracturing is an important research topic in solid mechanics and earthquake prediction.In this study,an EMR model of rock fracturing considering the fracture factor,elastic modulus,Poisson’s ratio,radiation distance and crack length is derived based on the Hertz oscillator array assumption.An experimental system,including an electromagnetic shielding module,an EMR signal induction and transmission module,a signal recording module and a loading module,is developed to understand the EMR characteristics of four different rocks.The validity of the EMR theoretical model is verified and the relationships between the rock cracking morphology and the EMR waveform,amplitude and frequency are revealed.It is found that rock mechanical properties have obvious influences on the EMR waveform,amplitude and frequency during rock fracturing.This study provides a better understanding on the EMR mechanism of rock fracturing and can help to improve the accuracy of rock disaster prediction based on EMR.
基金funded by Sichuan Institute of Geological Survey,China,grant number SCIGS-CZDXM-2025006the Natural Science Foundation of Sichuan Province(Sichuan Province Science and Technology Support Program),China,grant number 2024NSFSC1953.
文摘The seismic failure of jointed rock slopes is essentially a problem of dynamic fracturing and instability of discontinuous rock masses.In this study,seismic failures of anti-dip jointed rock slopes are numerically investigated by the sub-block splitting discontinuous deformation analysis(DDA)method.Firstly,diametrically compressive rock discs with a central pre-existing crack of different inclinations are simulated to verify the effectiveness of the sub-block splitting DDA method for rock fracturing simulations.Thereafter,the fracturing failure and instability process of five anti-dip jointed rock slopes with different configurations under the Wenchuan earthquake waves of different amplitudes are simulated.Results indicate that with larger excavation area of the slope and larger amplitude of the seismic loads,and under specific horizontal relative direction of the seismic wave to the slope(SSHRD),the slope stability will be dramatically reduced,and the failure mode will also be changed upon a basic mode of toppling.The surface and elevation amplification effects of the slope under seismic loads are successfully reproduced as well by the simulations.This work reveals the seismic failure process and mechanism of anti-dip jointed rock slopes,and could provide theoretical reference to the disaster prediction of anti-dip jointed rock slopes under earthquakes.
基金the National Natural Science Foundation of China(Grant No.41827806)and the Liaoning Revitalization Talent Program(Grant No.XLYC1801002).
文摘This study introduces a test system for microwave-induced fracturing of hard rocks under true triaxial stress.The test system comprises a true triaxial stress loading system,an open-ended microwaveinduced fracturing system,a data acquisition system,an acoustic emission(AE)monitoring system,and an auxiliary specimen loading system.Microwave-induced surface and borehole fracturing tests under true triaxial stress were fulfilled for the first time,which overcomes the problem of microwave leakage in the coupling loading of true triaxial stress and microwave.By developing the dynamic monitoring system,the thermal response and fracture evolution were obtained during microwave irradiation.The monitoring system includes the infrared thermometry technique for monitoring rock surface temperature,the distributed optic fiber sensing technique for monitoring temperature in borehole in rock,the AE technique and two-dimensional digital speckle correlation technique for monitoring the evolution of thermal damage and the rock fracturing process.To validate the advantages of the test system and investigate the characteristics of microwave-induced fracturing of hard rocks,the study demonstrates the experimental methods and results for microwave-induced surface and borehole fracturing under true triaxial stress.The results show that thermal cracking presented intermittent characteristics(calm eactiveecalm)during microwave-induced surface and borehole fracturing of basalt.In addition,true triaxial stress can inhibit the development and distribution of thermal cracks during microwave-induced surface fracturing.When microwave-induced borehole fracturing occurs,it promotes the distribution of thermal cracks in rock,but inhibits the width of cracks.The results also prove the reliability of the test system.
文摘The goal of this review paper is to provide a summary of selected discrete element and hybrid finitediscrete element modeling techniques that have emerged in the field of rock mechanics as simulation tools for fracturing processes in rocks and rock masses. The fundamental principles of each computer code are illustrated with particular emphasis on the approach specifically adopted to simulate fracture nucleation and propagation and to account for the presence of rock mass discontinuities. This description is accompanied by a brief review of application studies focusing on laboratory-scale models of rock failure processes and on the simulation of damage development around underground excavations.
基金National Key Research and Development Program of China,2020YFA0711800,Ting LiuNational Natural Science Foundation of China,52274241,Ting Liu,52474261,Ting Liu+2 种基金Basic Research Program of Jiangsu,BK20240207,Ting Liuthe Fundamental Research Funds for the Central Universities(2023KYJD1007)China Postdoctoral Science Foundation(2022M722672).
文摘To elucidate the dynamic characteristics of in-situ methane deflagration in coalbed methane wellbores and its mechanisms for fracturing coal rock,this study first developed a simulation experimental system specifically designed for methane in-situ deflagration fracturing.This experimental system,which is capable of withstanding pressures up to 150 MPa and meanwhile applying axial and confining pressures of up to 50 MPa to rock cores,enables the coupled simulation on methane deflagration and rock core fracturing processes.With the aid of this experimental system,physical simulation experiments on in-situ methane deflagration fracturing were conducted,and the following findings were obtained.Methane deflagration loads in enclosed wellbores exhibit characteristics of multi-level pulsed oscillation.With the rise of initial gas pressure,the peak deflagration load increases approximately linearly,with the pressure amplification factor spanning from 23.14 to 31.10,and its peak loading rate grows exponentially.Accordingly,the fracture volume and fracture porosity augment.To be specific,when the initial gas pressure rises from 0.6 to 2.4 MPa,the fracture volume and fracture porosity augment by factors of 14.0 and 8.73,respectively.The fractal dimension of spatial distribution of fractures also increases with the rise of deflagration load,indicating that a higher deflagration load conduces to the development of a larger and more complex fracture network.Methane deflagration fracturing is characterized as a composite fracture mode that involves the impact of strong stress waves and the driving force of high-pressure fluids.The primary factors influencing damage to coal-rock include the high-stress impact in the initial stage of deflagration,the fluid pressure driving effect in the middle stage,and the thermal shock resulting from high temperatures in the later stage.
基金supported by the National Natural Science Foundation of China(Grant No.41925012)Key task project for joint research and development of the Yangtze River Delta Science and Technology Innovation Community(Grant No.2022CSJGG1200)State Key Laboratory for GeoMechanics and Deep Underground Engineering(Grant No.SKLGDUEK2214).
文摘This study proposed a repeated adjustable mixture injection strategy(RAM)based microbial induced carbonate precipitation(MICP)for efficient mitigation of rock fracture leakage.Granite fractures with small apertures were investigated,and bio-sealing experiments were conducted using five different cementation solution(CS)concentrations(0.25−2 M).The results showed that the RAM-based bio-sealing method can seal and bond the small aperture rock fractures with high efficiency and uniform precipitation by adjusting the CS concentration.The RAM-based bio-sealing mechanism is attributed to the following four stages:(1)fixation of bacterial flocs onto the fracture surfaces,(2)precipitation of CaCO3 onto the fracture surfaces,(3)growth of pre-precipitated CaCO3 and adhesion of new-suspended CaCO3,and(4)bridging and clogging processes.The optimal CS concentration of 1 M resulted in a fracture filling rate up to 85%,a transmissivity reduction of 4 orders of magnitude,and a shear strength ranging from 512 kPa to 688 kPa.The bio-sealing effect was found to be influenced by the CS concentration on bacterial attachment,calcium carbonate yield and calcium carbonate bulk density.The CS concentration of 1 M promoted bacterial attachment,and increased calcium carbonate yield as well as calcium carbonate bulk density,while concentrations above 1 M had the opposite effect.The bulk density of calcium carbonate played a crucial role in the sealing and bonding performance of bio-sealed fractures,particularly at comparable filling ratios and bridging areas.The bulk density was regulated by the size of calcium carbonate crystals and was determined by Ca2+concentration in the CS.This study provides valuable insights into the RAM-based bio-sealing method,highlighting its potential for efficient rock fracture leakage mitigation through precise control of CS concentration and understanding the underlying mechanisms.
基金supported by the China Scholarship Council(CSC,Grant No.202108050072)JSPS KAKENHI(Grant No.JP19KK0121)。
文摘Grouting has been the most effective approach to mitigate water inrush disasters in underground engineering due to its ability to plug groundwater and enhance rock strength.Nevertheless,there is a lack of potent numerical tools for assessing the grouting effectiveness in water-rich fractured strata.In this study,the hydro-mechanical coupled discontinuous deformation analysis(HM-DDA)is inaugurally extended to simulate the grouting process in a water-rich discrete fracture network(DFN),including the slurry migration,fracture dilation,water plugging in a seepage field,and joint reinforcement after coagulation.To validate the capabilities of the developed method,several numerical examples are conducted incorporating the Newtonian fluid and Bingham slurry.The simulation results closely align with the analytical solutions.Additionally,a set of compression tests is conducted on the fresh and grouted rock specimens to verify the reinforcement method and calibrate the rational properties of reinforced joints.An engineering-scale model based on a real water inrush case of the Yonglian tunnel in a water-rich fractured zone has been established.The model demonstrates the effectiveness of grouting reinforcement in mitigating water inrush disaster.The results indicate that increased grouting pressure greatly affects the regulation of water outflow from the tunnel face and the prevention of rock detachment face after excavation.
基金support of this work by the National Natural Science Foundation of China (Grant Nos.41972316 and 41672252).
文摘The overall heat transfer coefficient(OHTC)of rock fractures is a fundamental parameter for characterizing the heat transfer behavior of rock fractures in hot dry rock(HDR)geothermal mining.Although a number of practical formulae for heat transfer coefficients have been developed in the literature,there is still no widely accepted analytical solution.This paper constructs highly accurate analytical solutions for the temperatures of the inner fracture wall and the fluid.Then they are employed to develop new definition-based formulae(formula A and its simplification formula B)of the OHTC,which are well validated by the experimental and numerical simulation results.An empirical correlation formula of heat transfer coefficient is proposed based on the definition-based formulae which can be directly used in the numerical simulations of heat transfer in rock fractures.A site-scale application example of numerical simulation also demonstrates the effectiveness of the empirical correlation formula.
基金funding from the European Research Council(ERC)under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST(grant agreement No.801809)support by MICIU/AEI/10.13039/501100011033 and by"European Union Next Generation EU/PRTR"through the‘Ramón y Cajal’fellowship(reference RYC2021-032780-I)+9 种基金funding by MICIU/AEI/10.13039/501100011033 and by“ERDF,EU”through the‘HydroPoreII’project(reference PID2022-137652NBC44)support by the Institute for Korea Spent Nuclear Fuel(iKSNF)National Research Foundation of Korea(NRF)grant funded by the Korea government(Ministry of Science and ICT,MSIT)(2021M2E1A1085196)support by the Swedish Radiation Safety(SSM),Swedish Transport Administration(Trafikverket),Swedish Rock Engineering Foundation(BeFo),and Nordic Energy Research(Grant 187658)supported by the US Department of Energy(DOE),the Officeof Nuclear Energy,Spent Fuel and Waste Science and Technology Campaign,and by the US Department of Energy(DOE),the Office of Basic Energy Sciences,Chemical Sciences,Geosciences,and Biosciences Division both under Contract Number DE-AC02-05CH11231 with Lawrence Berkeley National Laboratorysupport from the US National Science Foundation(grant CMMI-2239630)funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation programme(grant agreement No.101002507)the UK Natural Environment Research Council(NERC)for funding SeisGreen Project(Grant No.NE/W009293/1)which supported this workthe Royal Society UK for supporting this research through fellowship UF160443IMEDEA is an accredited"Maria de Maeztu Excellence Unit"(Grant CEX2021-001198,funded by MICIU/AEI/10.13039/501100011033).
文摘Coupled thermo-hydro-mechanical(THM)processes in fractured rock are playing a crucial role in geoscience and geoengineering applications.Diverse and conceptually distinct approaches have emerged over the past decades in both continuum and discontinuum perspectives leading to significant progress in their comprehending and modeling.This review paper offers an integrated perspective on existing modeling methodologies providing guidance for model selection based on the initial and boundary conditions.By comparing various models,one can better assess the uncertainties in predictions,particularly those related to the conceptual models.The review explores how these methodologies have significantlyenhanced the fundamental understanding of how fractures respond to fluid injection and production,and improved predictive capabilities pertaining to coupled processes within fractured systems.It emphasizes the importance of utilizing advanced computational technologies and thoroughly considering fundamental theories and principles established through past experimental evidence and practical experience.The selection and calibration of model parameters should be based on typical ranges and applied to the specificconditions of applications.The challenges arising from inherent heterogeneity and uncertainties,nonlinear THM coupled processes,scale dependence,and computational limitations in representing fieldscale fractures are discussed.Realizing potential advances on computational capacity calls for methodical conceptualization,mathematical modeling,selection of numerical solution strategies,implementation,and calibration to foster simulation outcomes that intricately reflectthe nuanced complexities of geological phenomena.Future research efforts should focus on innovative approaches to tackle the hurdles and advance the state-of-the-art in this critical fieldof study.
基金supported by the Program for Guangdong Introducing Innovative and Entrepreneurial Teams(2019ZT08G315)the National Natural Science Foundation of China(52304091,52004162 and 52274089)+1 种基金the Research Project of Education Department of Hunan Province(22B0427)the China postdoctoral science foundation(2023M741047).
文摘The fractured rock mass inherently exhibits uncertainty due to the presence of pre-existing discontinuities.In this study,a particle-based model incorporating the discrete fracture network(DFN)to elucidate the dynamic tensile responses and asso-ciated uncertainty of rock mass.At first,the particle-based model was used synthesize the intact rock and split Hopkinson pressure bar(SHPB)system,while the fractures were represented using the smooth fracture model(SJM).Subsequently,the samples of the fractured rock mass with varying joint geometrical configurations were conducted the dynamic tensile test using the numerical SHPB system.The simulated results demonstrate a gradual decrease in dynamic tensile strength(TS)with increasing fracture intensity and fracture length,which can be effectively described by nonlinear exponential func-tions.Additionally,the fracture orientation significantly influences the dynamic TS,however,the anisotropic characteristics gradually diminish as the deviation angle approaches 90°.Furthermore,as fracture intensity and fracture length increase,the dynamic TS variability also rises steadily.However,no noticeable pattern is seen when considering cases with varying fracture orientations.When subjected to SHPB loading,the fractured rock mass primarily exhibits a combined tensile-shear failure mode,contrasting with the pure tensile failure mode exhibited by the intact rock.These findings contribute signifi-cantly to comprehending the dynamic tensile responses of the fractured rock mass and can further enhance the stability analysis of in-situ rock engineering.
基金supported by National Natural Science Foundation of China(Grant Nos.52074312 and 52211530097)CNPC Science and Technology Innovation Foundation(Grant No.2021DQ02-0505).
文摘Wellbore breakout is one of the critical issues in drilling due to the fact that the related problems result in additional costs and impact the drilling scheme severely.However,the majority of such wellbore breakout analyses were based on continuum mechanics.In addition to failure in intact rocks,wellbore breakouts can also be initiated along natural discontinuities,e.g.weak planes and fractures.Furthermore,the conventional models in wellbore breakouts with uniform distribution fractures could not reflect the real drilling situation.This paper presents a fully coupled hydro-mechanical model of the SB-X well in the Tarim Basin,China for evaluating wellbore breakouts in heavily fractured rocks under anisotropic stress states using the distinct element method(DEM)and the discrete fracture network(DFN).The developed model was validated against caliper log measurement,and its stability study was carried out by stress and displacement analyses.A parametric study was performed to investigate the effects of the characteristics of fracture distribution(orientation and length)on borehole stability by sensitivity studies.Simulation results demonstrate that the increase of the standard deviation of orientation when the fracture direction aligns parallel or perpendicular to the principal stress direction aggravates borehole instability.Moreover,an elevation in the average fracture length causes the borehole failure to change from the direction of the minimum in-situ horizontal principal stress(i.e.the direction of wellbore breakouts)towards alternative directions,ultimately leading to the whole wellbore failure.These findings provide theoretical insights for predicting wellbore breakouts in heavily fractured rocks.
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.
基金supported by the National Natural Science Foundation of China(Grant No.42202316)the China Postdoctoral Science Foundation(Grant No.2022M712963)the Open Fund of Badong National Observation and Research Station of Geohazards(Grant No.BNORSG-202309).
文摘Non-Darcian flow in rock fractures exhibits significant anisotropic characteristics,which can be affected by mechanical processes,such as cyclic shearing.Understanding the evolution of anisotropic nonDarcian flow is crucial for characterizing groundwater flow and mass/heat transport in fractured rock masses.In this study,we conducted experiments on non-Darcian flow in single rough fractures under cyclic shearing conditions,aiming to analyze the anisotropic evolution of inertial permeability and viscous permeability.We established quantitative characterization models for the two types of permeability.First,we conducted cyclic shearing experiments on four sets of 24 rough rock fractures,investigating their shear characteristics.Then,we performed 480 non-Darcian flow experiments to analyze the anisotropic evolution of viscous permeability and inertial permeability of these rock fractures.The results showed that viscous permeability exhibited significant differences only in the orthogonal direction,while inertial permeability exhibited differences in both orthogonal and opposite directions.With increase in the shear cycles,the differences in the orthogonal direction gradually increased,while those in opposite direction gradually decreased.Finally,we established characterization equations for the two permeabilities based on the proposed directional geometric parameters and validated the performance of these equations with experimental data.These findings are useful for the quantitative characterization of the evolution of non-Darcian flow in fractures under dynamic loading conditions.
基金Open Fund of Badong National Observation and Research Station of Geohazards,Grant/Award Number:BNORSG202315Key R&D Program of Xinjiang Uygur Autonomous Region,Grant/Award Number:2021B03004-3+1 种基金National Natural Science Foundation of China,Grant/Award Numbers:42207169,U22A20569Natural Science Foundation of Jiangsu Province,Grant/Award Number:BK20221126。
文摘The shear characteristics of bolted rock joints are crucial for the stability of tunneling and mining,particularly in deep underground engineering,where rock bolt materials are exposed to high stress,water pressure,and engineering disturbance.However,due to the complex interaction between bolted rock joints and various geological contexts,many challenges and unsolved problems arise.Therefore,more investigation is needed to understand the shear performance of bolted joints in the field of deep underground engineering.This study presents a comprehensive review of research findings on the responses of bolted joints subjected to shearing under different conditions.As is revealed,the average shear strength of bolted rock joints increases linearly with the normal stress and increases with the compressive strength of rock until it reaches a stable value.The joint roughness coefficient(JRC)affects the contact area,friction force,shear strength,bending angle,and axial force of bolted rock joints.A mathematical function is proposed to model the relationship between JRC,normal load,and shear strength.The normal stress level also influences the deformation model,load-carrying capacity,and energy absorption ratio of bolts within bolted rock joints,and can be effectively characterized by a two-phase exponential equation.Additionally,the angle of the bolts affects the ratio of tensile and shear strength of the bolts,as well as the mechanical behavior of both bolted rock joints and surrounding rock,which favors smaller angles.This comprehensive review of experimental data on the shear behavior of bolted rock joints offers valuable theoretical insights for the development of advanced shear devices and further pertinent investigations.
基金funded by the National Natural Science Foundation of China(Grant Nos.52278398 and U23A0664).
文摘To evaluate the thermal behavior of tunnels,an equivalent thermal conductivity(ETC)model for the fractured rock masses surrounding tunnels was proposed,based on the series-parallel theory,which incorporates the heat transfer characteristics of the surrounding rock.A thermal probe test(TPT)was subsequently conducted at the Dajian Mountain Tunnel(China),and the heat transfer model of the thermal probe was developed and calibrated based on the TPT results.The ETCs of different test areas in the borehole were calculated based on the fracture parameters(dip direction,dip angle,opening,trace length),obtained via a digital borehole photography test.Finally,the new ETC model,the volumeaveraged model,and the non-fracture model were compared for accuracy in heat transfer calculation.The results demonstrate that(1)the error of heat transfer calculation error was reduced by 17.2%e69.2%using the new ETC model.(2)For the ETCs of different thermal response test areas,the minimum and maximum values were 2.15 W/(m K)and 3.7 W/(m K),respectively,with the fracture effect causing up to a 41.2%reduction in thermal conductivity.(3)For the ETC of the borehole,the ETC value was 2.53 W/(m K),with the fracture effect leading to a 31.6%reduction in thermal conductivity.The effect of fractures on the thermal conductivity of rock mass could not be ignored.This ETC model addresses the challenge of determining the ETC for the heterogeneous surrounding rock of tunnels and provides a more accurate representation of the in situ thermal behavior of tunnels.
基金supported by the National Key Research and Development Program Young Scientist Project(2024YFC2911000)the Natural Science Foundation of Shandong Province(ZR2024ME031)+1 种基金National Natural Science Foundation of China(52474103)Natural Science Foundation of Shandong Province(ZR2024ZD22).
文摘The shear behavior of fractured rock masses critically infuences engineering stability,particularly in slope engineering.Overcoming limitations of conventional preparation methods,this study utilizes sand-powder 3D printing to fabricate rocklike specimens with controlled internal fractures.Direct shear tests systematically investigate fracture radius and number efects on strength evolution under constant density,with quantitative analysis revealing their diferential contributions.The results show that:(1)The failure of sand-powder 3D-printed fractured rock-like specimens exhibits brittle characteristics.The shear stress-shear displacement relationship can be divided into fve stages:compaction,elasticity,unstable development,peak,and post-peak.Crack initiation and propagation primarily occur from the late elastic stage to the peak stage.(2)An increase in fracture radius signifcantly reduces pre-peak shear stifness,resulting in a smoother curve progression,while changes in fracture number have minimal impact on the stage-specifc characteristics of the shear curve.(3)Shear strength decreases exponentially with increasing fracture radius,whereas an increase in fracture number leads to a linear reduction in shear strength.Moreover,the weakening efect of fracture number on shear strength becomes more pronounced with larger fracture radius.(4)Quantitative analysis shows that the infuence of fracture radius on shear strength is 2.4 times greater than that of fracture number.This study broadens the understanding of the shear behaviors of fractured rock masses and reveals the key infuence mechanism of fracture density on rock mass deformation and failure,and provides theoretical guidance for slope stability analysis and rock mass engineering design.
基金supported by the Research Fund for the Doctoral Program of Higher Education of China (20090101120057)the Scientific Research Fund of Zhejiang Provincial Education Department (Y200909163)
文摘A complete rock failure process usually involves opening/sliding of preexisting discontinuities as well as frac- turing in intact rock bridges to form persistent failure sur- faces and subsequent motions of the generated rock blocks. The recently developed numerical manifold method （NMM） has potential for modelling such a complete failure process. However, the NMM suffers one limitation, i.e., unexpected material domain area change occurs in rotation modelling. This problem can not be easily solved because the rigid body rotation is not represented explicitly in the NMM. The discontinuous deformation analysis （DDA） is specially de- veloped for modelling discrete block systems. The rotation- induced material area change in the DDA modelling can be avoided conveniently because the rigid body rotation is represented in an explicit form. In this paper, a transition technique is proposed and implemented to convert a NMMmodelling to a DDA modelling so as to simulate a complete rock failure process entirely by means of the two methods, in which the NMM is adopted to model the early fracturing as well as the transition from continua to discontinua, while the DDA is adopted to model the subsequent motion of the generated rock blocks. Such a numerical approach also im- proves the simulation efficiency greatly as compared with a complete NMM modelling approach. The fracturing of a rock slab with pre-existing non-persistent joints located on a slope crest and the induced rockfall process are simulated. The validity of the modelling transition from the NMM to the DDA is verified and the applicability of the proposed nu- merical approach is investigated.
