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Frictional characteristics of rough granite fractures subjected to various normal loading/unloading rates and shear velocities 认领 引用
1
作者 ZHANG Chuan-jiu DUAN Hong-fei +5 位作者 LI Xing-ling BAI Zhen-chao LI Peng WANG Wei LI Xuan-liang DANG Wen-gang 《Journal of Central South University》 SCIE EI CAS CSCD 2026年第5期2243-2266,共24页
The shear behavior of rock joints under dynamic disturbances is still not well understood,especially when subjected to irregular stress waveforms,which are common in real-world scenarios.In this study,a series of cycl... The shear behavior of rock joints under dynamic disturbances is still not well understood,especially when subjected to irregular stress waveforms,which are common in real-world scenarios.In this study,a series of cyclic normal loading/unloading direct shear tests was conducted on rough granite fractures using a laboratory direct shear apparatus.The effects of different normal loading rates,unloading rates,and shear velocities on shear stress,apparent friction coefficient,normal displacement,and shear work were systematically analyzed.The experimental results indicated that as the normal loading and unloading rates increase and the shear velocity decreases,the peak shear stress and shear work decrease.Compared with quasi-static shear strength,dynamic normal stress disturbance may strengthen the dynamic shear strength or weaken it,and the strengthening/weakening degree is controlled by the normal loading/unloading rates and shear velocity.Furthermore,three distinct shear stress variation patterns(linear decay,nonlinear decay,and peak delay)are observed.These findings provide a theoretical basis for evaluating the stability of jointed rock masses under complex dynamic disturbances such as earthquakes,tidal effects,traffic loads,and blasting activities. 展开更多
关键词 rough granite fracture normal loading/unloading rates shear velocity frictional strengthening frictional weakening
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An experimental study of the dynamic features of shadow areas of caustics in response to loading/unloading fracture 认领 引用
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作者 许昭永 杨润海 +4 位作者 赵晋明 王赟赟 熊秉衡 王正荣 梅世蓉 《Acta Seismologica Sinica(English Edition)》 2002年第2期198-209,共12页
Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation z... Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation zone (shadow area) when the sample fractures during loading (loading-fracture) and unloading (unloading-fracture) are studied visually. The results show that the strain nuclei (zones with dense fringes) appear first at the tips of prefabricated cracks at low stress, and then the shadow areas of caustics form with the increase of load. These nuclei and shadow areas can become larger, or smaller, when the process of loading, or unloading, goes on. When the stress is kept within a certain range, the shadow areas of caustics can become larger and smaller alternatively with repeated loading and unloading (cyclic loading). However, when loading and unloading at high stress, in particular when the macrofracture is about to appear, the variations of the shadow areas of caustics are irreversible and quite different. The shadow areas of caustics expand rapidly at an increasing speed when loading-fracture appears. In contrast, the shadow areas of caustics expand at a lower speed when unloading-fracture appears; besides, there is a circular shadow in front of the sharp-angle shaped area. 展开更多
关键词 loading-fracture unloading-fracture shadow areas of caustics dynamic stress field
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Characterization of rock damage evolution and support timing under true triaxial unloading paths 认领 引用
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作者 QI Min-jie ZHAO Guang-ming +6 位作者 MENG Xiang-rui LIU Chong-yan XU Wen-song XU Xin ZHAO Cong-hui SUN Kai ZHAO Bin 《Journal of Central South University》 SCIE EI CAS CSCD 2026年第1期442-465,共24页
To study the influence of support timing and support strength on the mechanical properties and deformation damage characteristics of a single-sided unloaded rock mass,a true triaxial perturbation unloaded rock testing... To study the influence of support timing and support strength on the mechanical properties and deformation damage characteristics of a single-sided unloaded rock mass,a true triaxial perturbation unloaded rock testing system was used to conduct rock damage tests on sandstone with different support timing and strength paths.Based on the acoustic emission monitoring system,the spatial and temporal evolution characteristics of the whole process of rock body loaded instability under two stress paths were studied,and the mechanism of the reinforcing effect of stress support on the unloaded rock mass was analyzed.The results show that,within the scope of this study,both earlier applications of shoring and an increase in shoring strength can effectively improve the ultimate bearing capacity of the unloaded rock,which increases the ultimate bearing capacity of the unloaded rock mass by 60.31% and 54.96%,respectively;There is a phenomenon of rebound deformation of the rock mass during sudden changes in stress(single-sided unloading,stress support),which shows opposite expansion and compression platforms on the stress−strain curve;The crack evolution of unloaded rock under different stress support conditions shows the state law of"initial crack activation→middle steady state expansion→late main crack penetration",and the lagging support significantly accelerates the crack evolution from local activation to main penetration;The single-sided unloading and stress-supporting stages have less influence on the unloading deformationsσ1u,σ2u and support deformationsσ1 t,σ2t in theσ1 andσ2directions,while they show significant response characteristics toσ3u,σvu and σ3 t,σvt,and with the increase of the support strength,the stress-supporting stagesσ3 t,σvt gradually increase and exceed the deformations generated by the unloading stagesσ3u,σvu;The increase of support strength can effectively compensate for the rock stress loss caused by unloading,which makes the maximum,minimum,and volumetric strain support coefficients during the loading and unloading of the rock body increase gradually while the effect on the intermediate principal strain support coefficient is small;During loading,the support strength of rock masses seeks a new bearing area by regulating stress equilibrium states.This process primarily manifests as a shift in the locations of the crushing zone and the main bearing area,accompanied by a corresponding transformation in failure patterns.Consequently,the rock mass transitions from asymmetric three-zone damage under no or weak support to approximate symmetric three-zone damage under strong support.Simultaneously,the main load-bearing area of the rock mass shifts from deep bearing in the unsupported to middle bearing under strong support as the support strength increases. 展开更多
关键词 true triaxial single-sided unloading unloading effect support timing support strength
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Anisotropic mechanical behaviour of Callovo-Oxfordian claystone under triaxial lateral unloading 认领 引用
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作者 Hao Wang Yu-Jun Cui +2 位作者 Patrick Dangla Minh Ngoc Vu Jean Talandier 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2026年第5期3882-3890,共9页
Callovo-Oxfordian(COx)claystone has been selected as the host rock formation for the deep geological disposal of radioactive waste in France,called the Cigéo project.The excavation of drifts in the COx formation ... Callovo-Oxfordian(COx)claystone has been selected as the host rock formation for the deep geological disposal of radioactive waste in France,called the Cigéo project.The excavation of drifts in the COx formation induced damage zones with an anisotropic shape,while the stress state around the drifts is almost isotropic.This is due to the anisotropic properties of the host rock formation and the instability caused by the brittle damage.In this study,the mechanical anisotropy of COx claystone was investigated through a triaxial shear test,where the axial stress was maintained while the lateral stress was decreased.Such a method was proposed for simulating one of the possible unloading paths involved during the excavation.The triaxial samples were prepared along different directions based on the angle between the axial loading direction and the one perpendicular to the bedding plane.Results show that the stress-strain curve exhibited an elasto-plastic pattern.With increasing deviatoric stress,a minor decline in Young's modulus E was observed,suggesting progressive damage behaviour.The shear strength changed with increasing the loading angle,showing the anisotropic property of COx claystone.Moreover,the results in this study and collected from other works show a time-dependent behaviour of COx claystone.It is attributed to the coupled effect of creep and pore pressure dissipation inside claystone. 展开更多
关键词 Callovo-Oxfordian claystone Triaxial unloading Anisotropy Young's modulus Shear strength Cigéo
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Damage evolution law under unloading confining pressure of cemented backfill based on energy dissipation 认领 引用
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作者 LIU Wei-zhen GONG Bin +3 位作者 NIU Shi-wei WANG Hui-qin LI Hong-rui HU Zhong-jing 《Journal of Central South University》 SCIE EI CAS CSCD 2026年第1期400-421,共22页
High ground temperature and unloading disturbance have emerged as critical factors impacting the property of cemented gauge-fly ash backfill(CGFB).The characteristics of energy and damage in CGFB were analyzed under c... High ground temperature and unloading disturbance have emerged as critical factors impacting the property of cemented gauge-fly ash backfill(CGFB).The characteristics of energy and damage in CGFB were analyzed under conditions of high ground temperature and unloading by conducting triaxial unloading tests with different initial confining pressures on CGFB that had been cured at various temperatures.Based on dissipative energy,triaxial unloading confining pressure damage constitutive model of CGFB was constructed.It has been demonstrated that the ratio of elastic strain energy in CGFB decreases and the ratio of dissipated energy increases at the end of unloading increases under higher curing temperature.The change in the elastic energy consumption ratio curve of CGFB,which shifts from a gradual increase to a swift rise at a certain"inflection point",can be utilized as a criterion for evaluating the failure of the unloading strength of CGFB.The triaxial unloading damage constitutive model for CGFB divides the damage progression into three distinct phases:initial damage stage,accelerated damage development stage,and rapid damage growth stage.The research findings offer a theoretical foundation for evaluating the extent of damage to CGFB caused by the combined influences of elevated ground temperature and unloading. 展开更多
关键词 curing temperature cemented gangue-fly ash backfill unloading confining pressure dissipated energy damage constitutive model
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Failure characteristics and the energy criterion of rock with a through-going joint under true-triaxial unloading conditions:Insights from the DEM model 认领 引用
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作者 Fei Liu Changhui Liang +2 位作者 Sijia Liu Yongjun Zhang Luo Wang 《Deep Underground Science and Engineering》 EI CAS CSCD 2026年第2期465-481,共17页
Excavation unloading damages rock masses,with preferential failure along geological defects in rock engineering,which may induce catastrophe geological hazards.It is important to study the failure of jointed rock unde... Excavation unloading damages rock masses,with preferential failure along geological defects in rock engineering,which may induce catastrophe geological hazards.It is important to study the failure of jointed rock under true-triaxial unloading conditions.3D DEM true-triaxial unloading modeling tests on rock with through-going joint considering the contributing factors,that is,the joint inclination,the initial confining pressure,and the unloading point,were conducted to study the rock mechanical properties,cracking behaviors,and failure characteristics.Six typical rock failure modes were summarized based on the development of main cracks,and the associated cracking mechanisms were studied by analysis of the ratio of tensile crack to shear crack.An energy criterion determining whether unloading-induced rock failure occurs instantaneously was proposed by comparing the accumulated elastic strain energy at the unloading point in true-triaxial unloading simulations with the limit elastic strain energy stored in rocks in biaxial compression modeling tests.Furthermore,the strength characteristics and applicability of the Mogi–Coulomb failure criterion in describing the failure of specimens with through-going joint under true-triaxial unloading conditions were studied.This study provides some new insights into true-triaxial unloading-induced failure of jointed rock,which may be valuable for revealing the mechanism of rock instabilities influenced by geological defects in deep excavations. 展开更多
关键词 cracking behavior energy criterion joint rock failure mode true-triaxial unloading modeling test
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Loading-unloading responses of non-persistent flawed granite subjected to cyclic disturbances 认领 引用
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作者 Tingting Liu Chao Zhang +3 位作者 Luyang Ding Kun Xu Xinping Li Wenxu Huang 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2026年第5期3589-3605,共17页
During geotechnical construction,flawed rock masses experience dynamic cyclic disturbances,leading to cumulative deformation and progressive damage.Consequently,elucidating the fracture mechanisms under cyclic loading... During geotechnical construction,flawed rock masses experience dynamic cyclic disturbances,leading to cumulative deformation and progressive damage.Consequently,elucidating the fracture mechanisms under cyclic loading is crucial for ensuring the safety and prolonged operation of deep underground engineering.This study investigated the mechanical responses of the surrounding rock at different locations by conducting triaxial tests on flawed granite using three distinct cyclic loading and unloading paths.Based on the maximum tangential stress criterion,a fracture mechanics model for open flaws was developed to analyze the intrinsic influence of confining pressure and flaw inclination on crack initiation behavior.The results indicate that graded unloading of confining pressure significantly weakens the flawed rock mass,reducing its peak stress to only 77.5%of that observed under constant confining pressure.Conversely,flawed rock masses exhibit a substantial increase in bearing capacity under increasing graded cyclic loading,achieving a peak stress 19.3%higher than that under cyclic disturbance loading.At a constant confining pressure of 40 MPa,the type of disturbance loading has no significant effect on the failure mode.The flawed granite specimens form a nearly V-shaped shear failure zone along the open flaw.However,confining pressure unloading induced a more complex shear-tensile composite failure mode in the specimens.The crack initiation angle increases nonlinearly with confining pressure,but decreases gradually as the flaw inclination angle(β)increases.These findings provide valuable insights for the safe construction of deep underground engineering. 展开更多
关键词 Flawed granite Cyclic disturbance loading Energy evolution Fracture mechanism Crack initiation angle
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Mechanical behavior and acoustic emission characteristics of initially damaged coal under triaxial cyclic loading and unloading 认领 引用 被引量：1
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作者 Qican Ran Yunpei Liang +5 位作者 Quanle Zou Chunfeng Ye Zihan Chen Tengfei Ma Zhaopeng Wu Bichuan Zhang 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2026年第1期230-245,共16页
During deep coal mining,an instability failure of coal usually occurs under the combined effect of initial damage and triaxial cyclic loading and unloading(TCLU).Therefore,this study investigated the impact of initial... During deep coal mining,an instability failure of coal usually occurs under the combined effect of initial damage and triaxial cyclic loading and unloading(TCLU).Therefore,this study investigated the impact of initial damage on mechanical behavior and acoustic emission(AE)characteristics of coal under TCLU.Initial damage variables(IDVs)of coal specimens were quantified using preloading,followed by TCLU experiments to assess the deformation,energy distribution,and fracture development.The results revealed that the increase in IDVs significantly reduced the structural integrity of coal specimens,increased the cumulative irreversible strain,and enhanced the dissipated energy owing to microfracture expansion.Moreover,AE monitoring showed earlier activation of fractures and a higher occurrence of large-scale rupture events of coal specimens with high IDVs,which correlated with decreasing AE b values(reflecting the different scales of fracture within specimens)and increasing S values(reflecting the AE activity within specimens).Additionally,computed tomography analysis revealed intensified fracture networks and increasing three-dimensional fractal dimensions of coal specimens with higher IDVs.Finally,the coupling effect of TCLU and initial damage on the weakening mechanism of coal was investigated.Initial damage significantly reduced the structural integrity of coal by increasing the number of weak planes within coal specimens,contributing to the earlier activation and rapid expansion of fractures at low stress levels under TCLU and eventually accelerating the weakening process of coal.This study provides a scientific basis and theoretical support for the prevention and control of dynamic disasters in deep coal mining. 展开更多
关键词 Triaxial cyclic loading Initially damaged coal Linear energy storage(LES) Acoustic emission(AE) Computed tomography(CT)
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Analysis of rock burst ejection behavior and stress-energy response of coal under true triaxial loading-unloading conditions 认领 引用
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作者 XU Wen-tao CHENG Yun-hai +1 位作者 XU Wen-song PAN Cheng 《Journal of Central South University》 SCIE EI CAS CSCD 2026年第5期2210-2230,共21页
In order to explore the ejection failure mechanism and energy variation law of the in-focused energy rock burst and the concentrated stress rock burst,based on the true triaxial disturbance unloading rock test system,... In order to explore the ejection failure mechanism and energy variation law of the in-focused energy rock burst and the concentrated stress rock burst,based on the true triaxial disturbance unloading rock test system,high-stress unloading and different second principal stress loading tests were conducted.The mechanical properties and AE characteristics of coal samples under high-stress unloading and varying secondary principal stress loading conditions have been systematically analyzed.The energy of the loaded coal sample was calculated by the area of the loading and unloading curve.The elastic energy and dissipation energy ratio,the pre-peak energy and post-peak energy ratio,and the dissipation energy and elastic energy ratio are used to characterize the energy accumulation,dissipation,and release behavior.The energy mutation mechanism of coal samples under different loading and unloading conditions is revealed.The results indicate that the ejection failure characteristics exhibit the characteristics of tension-shear composite failure,in which tension failure is an inevitable occurrence during the ejection failure process.Unloading is more sensitive to energy accumulation ejection failure,and the ejection failure phenomenon tends to become more evident as the unloading degree deepens.The second principal stress has a great influence on the ejection failure of stress concentration rock burst,and the intensity of ejection failure increases with the increase of the second principal stress.The energy variation law of coal samples under high stress unloading and different second principal stress loading conditions is similar.With the increase in coal sample strength,the kinetic energy,impact tendency,and ejection failure probability of coal sample ejection fragments also increase.The more fully damaged after unloading,the more prone to ejection.The evolution characteristics of AE have three stages,i.e.,rising period,quiet period,and destruction,in which the local ejection phenomenon appears in the destruction stage.The research method is a certain rationality for the analysis of the energy evolution mechanism of coal rock.The research results provide an experimental basis for the ejection failure of rock bursts and support for targeted classified control measures. 展开更多
关键词 deep coal mass true triaxial different principal stresses unloading rock burst
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Experimental study on failure precursory characteristics and moisture content effect of pre-cracked rocks under graded cyclic loading and unloading 认领 引用 被引量：4
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作者 Wei Zhang Dongxiao Zhang +1 位作者 Weiyao Guo Baoliang Zhang 《International Journal of Mining Science and Technology》 SCIE EI CAS CSCD 2025年第2期249-264,共16页
It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and ... It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass.Based on digital speckle correlation(DSCM),acoustic emission(AE)and electromagnetic radiation(EMR),uniaxial hierarchical cyclic loading and unloading tests were carried out on sandstones with different fracture numbers under dry,natural and saturated water content,to explore the fracture propagation,failure precursor characteristics and damage response mechanism under the influence of water content effect.The results show that with the increase of water content,the peak stress and crack initiation stress decrease gradually,and the decreases are 15.28%-21.11%and 17.64%-23.04%,respectively.The peak strain and crack initiation strain increase gradually,and the increases are 19.85%-44.53%and 19.15%-41.94%,respectively.The precracked rock with different water content is mainly characterized by tensile failure at different loading stages.However,with the increase of water content,the proportion of shear cracks gradually increases,while acoustic emission events gradually decrease,the dissipative energy and energy storage limits of the rock under peak load gradually decrease,and the charge signal increases significantly,which is because the lubrication effect of water reduces the friction coefficient between crack surfaces. 展开更多
关键词 Damage mechanisms Pre-cracked rocks Crack propagation Water-rock interaction Graded cyclic loading and unloading
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Microstructure evolution in anisotropic tight sandstones under hydrostatic loading and unloading processes 认领 引用 被引量：1
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作者 Xiaying Li Haimeng Shen Qi Li 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2025年第3期1528-1538,共11页
Preexisting cracks inside tight sandstones are one of the most important properties for controlling the mechanical and seepage behaviors.During the cyclic loading process,the rock generally exhibits obvious memorabili... Preexisting cracks inside tight sandstones are one of the most important properties for controlling the mechanical and seepage behaviors.During the cyclic loading process,the rock generally exhibits obvious memorability and irreversible plastic deformation,even in the linear elastic stage.The assessment of the evolution of preexisting cracks under hydrostatic pressure loading and unloading processes is helpful in understanding the mechanism of plastic deformation.In this study,ultrasonic measurements were conducted on two tight sandstone specimens with different bedding orientations subjected to hydrostatic loading and unloading processes.The P-wave velocity was characterized by a similar response with the volumetric strain to the hydrostatic pressure and showed different strain sensitivities at different loading and unloading stages.A numerical model based on the discrete element method(DEM)was proposed to quantitatively clarify the evolution of the crack distribution under different hydrostatic pressures.The numerical model was verified by comparing the evolution of the measured P-wave velocities on two anisotropic specimens.The irreversible plastic deformation that occurred during the hydrostatic unloading stage was mainly due to the permanent closure of plastic-controlled cracks.The closure and reopening of cracks with a small aspect ratio account for the major microstructure evolution during the hydrostatic loading and unloading processes.Such evolution of microcracks is highly dependent on the stress path.The anisotropy of the crack distribution plays an important role in the magnitude and strain sensitivity of the P-wave velocity under stress conditions.The study can provide insight into the microstructure evolution during cyclic loading and unloading processes. 展开更多
关键词 Plastic deformation P-wave velocity Discrete element method(DEM) Cyclic loading and unloading Crack evolution
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Creep constitutive model of yellow sandstone under coupling action of unloading and wet-dry cyclic damage 认领 引用 被引量：2
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作者 QIN Zhe LIU Zhen +1 位作者 ZHANG Run-chang FU Hou-li 《Journal of Mountain Science》 SCIE CSCD 2025年第3期1087-1100,共14页
The study focuses on the creep characteristics of significant yellow sandstone for water conservancy, hydropower, and other waterrelated slope excavation unloading rock-graded loading creep characteristics. It conduct... The study focuses on the creep characteristics of significant yellow sandstone for water conservancy, hydropower, and other waterrelated slope excavation unloading rock-graded loading creep characteristics. It conducts a uniaxial graded loading creep test on yellow sandstone under different pre-peak unloading and wetting-drying cycles. The improved nonlinear Nishihara model was obtained by introducing a nonlinear viscous element with an accelerated creep threshold switch. The sensitivity characteristics of the parameters of the improved creep model were analyzed and a nonlinear creep constitutive model was established, considering the unloading-cyclic intrinsic damage induced by water intrusion. The research results show that:(1)With an increase in the unloading point, the porosity of the rock samples initially decreases and then increases. As the number of cyclic water intrusions rises, the porosity of the rock samples gradually increases, reaching a maximum of 9.58% at an unloading point of 70% uniaxial compression stress(0.7 Rc) after five cycles.(2) Total creep deformation increases with the number of cyclic water intrusions;however, with an increase in the unloading ratio, the original samples show an initial decrease, followed by an increase in creep deformation. With a higher unloading ratio and various instances of cyclic water intrusion, the total creep time of the rock samples,compared to the original samples, is reduced by 21.8%and 23.02%. The creep damage mode gradually changes from shear damage to tensile damage.(3) The sensitivity characteristics of the improved creep model parameters show that transient elasticity modulus E1 is affected by the coupling of unloading and cyclic water intrusion. The viscoelastic modulus E2 and viscous coefficient η1 are mainly affected by unloading and cyclic water intrusion.(4) Based on the strain equivalence principle of damage mechanics, the damage treatment of the parameters in the original model is improved to construct a nonlinear creep constitutive model that considers unloading-cyclic water intrusion damage. A parameter inversion and comparison to the traditional Nishihara model reveal an average relative standard deviation of 0.271%,significantly less than 1%, indicating a more accurate nonlinear creep constitutive model. The research results are crucial for analyzing the long-term stability of water-related steep rocky slopes post-excavation and unloading and for preventing and controlling creep-type landslide disasters. 展开更多
关键词 Pre-peak unloading Dry and wet cycles Creep test Deformation characteristics Creep constitutive model
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True triaxial unloading test on the mechanical behaviors of sandstone:Effects of the intermediate principal stress and structural plane 认领 引用 被引量：1
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作者 Fan Feng Zhiwei Xie +3 位作者 Shaojie Chen Diyuan Li Siyu Peng Tong Zhang 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2025年第4期2208-2226,共19页
A series of true triaxial unloading tests are conducted on sandstone specimens with a single structural plane to investigate their mechanical behaviors and failure characteristics under different in situ stress states... A series of true triaxial unloading tests are conducted on sandstone specimens with a single structural plane to investigate their mechanical behaviors and failure characteristics under different in situ stress states.The experimental results indicate that the dip angle of structural plane(θ)and the intermediate principal stress(σ2)have an important influence on the peak strength,cracking mode,and rockburst severity.The peak strength exhibits a first increase and then decrease as a function ofσ2 for a constantθ.However,whenσ2 is constant,the maximum peak strength is obtained atθof 90°,and the minimum peak strength is obtained atθof 30°or 45°.For the case of an inclined structural plane,the crack type at the tips of structural plane transforms from a mix of wing and anti-wing cracks to wing cracks with an increase inσ2,while the crack type around the tips of structural plane is always anti-wing cracks for the vertical structural plane,accompanied by a series of tensile cracks besides.The specimens with structural plane do not undergo slabbing failure regardless ofθ,and always exhibit composite tensile-shear failure whatever theσ2 value is.With an increase inσ2 andθ,the intensity of the rockburst is consistent with the tendency of the peak strength.By analyzing the relationship between the cohesion(c),internal friction angle(φ),andθin sandstone specimens,we incorporateθinto the true triaxial unloading strength criterion,and propose a modified linear Mogi-Coulomb criterion.Moreover,the crack propagation mechanism at the tips of structural plane,and closure degree of the structural plane under true triaxial unloading conditions are also discussed and summarized.This study provides theoretical guidance for stability assessment of surrounding rocks containing geological structures in deep complex stress environments. 展开更多
关键词 True triaxial unloading Dip angle of structural plane Intermediate principal stress Mechanical behaviors Cracking modes Failure criterion
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Mechanical properties and dilatancy angle model of jointed hard rock under true triaxial cyclic loading and unloading 认领 引用
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作者 Hong Xu Gang Wang +3 位作者 Quan Jiang Shili Qiu Guangliang Feng Xiang Huang 《International Journal of Coal Science & Technology》 SCIE EI CAS CSCD 2025年第6期95-108,共14页
Joints play a crucial role in the stability of surrounding rock in deep underground engineering.Studying the mechanical properties and evolution laws of rocks with different joint characteristics under true triaxial s... Joints play a crucial role in the stability of surrounding rock in deep underground engineering.Studying the mechanical properties and evolution laws of rocks with different joint characteristics under true triaxial stress is highly significant.This paper presents the results of a series of true triaxial cyclic loading and unloading experiments conducted on natural stiff-jointed and artificially jointed granite,where the correlation between fracture characteristics and joint inclination was investigated.It was observed that the peak strength,plastic volumetric strain,and failure mode of the jointed granite varied considerably with joint inclination.This underscores the significant influence of joint inclination on the mechanical behavior of deep granite.Building upon a comprehensive understanding of the strength characteristics and deformation evolution in jointed granite with varying inclinations,a new dilation angle model was developed,incorporating the coupling effects of plastic volumetric strain and joint inclination.A strong agreement was found between our theoretical predictions and test data,suggesting that the proposed dilation angle model can effectively describe the dilatancy characteristics of granite with joints.This study is anticipated to offer a theoretical basis for excavation and support design,as well as stability analysis of deep jointed rock masses. 展开更多
关键词 True triaxial cyclic loading and unloading Joints Inclination Plastic volumetric strain Dilation angle
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Fracture damage and energy evolution of fissured coal subject to triaxial unloading condition 认领 引用
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作者 Zhijie Zhu Peng Wang +5 位作者 Xiaohan Yang Jan Nemcik Ting Ren Laigui Wang Jun Han Songsong Guan 《International Journal of Coal Science & Technology》 SCIE EI CAS CSCD 2025年第2期255-268,共14页
Fissured coal mass under triaxial unloading condition exhibits higher burst potential than the triaxial loading condition,which poses challenge to safety and productivity of resources extraction and underground space ... Fissured coal mass under triaxial unloading condition exhibits higher burst potential than the triaxial loading condition,which poses challenge to safety and productivity of resources extraction and underground space utilization.To comprehensively understand the mechanism of unloading-induced burst during excavation process,this study investigated the fracture and energy evolution of samples with different fissure types such as single,two parallel,and two coplanar-parallel using PFC2D modelling.Triaxial loading tests were conducted to determine the compressive strengths and other parameters.With increase of fissure inclination angle,the triaxial compressive strength decreases forβ=0°-30°,and then increase forβ=30°-90°.The strength of samples with two coplanar-parallel fissures is the highest.Fissure can significantly change the distribution of fracture and elastic energy.Secondary cracks were generated starting from both ends of the fissure.Forβ=0°-60°,low elastic strain energy area was produced around the fissure along the loading direction.The elastic strain energy is transferred to the outside of fissures.Forβ=75°-90°,only a small amount of high elastic strain energy was generated on both sides of the fissure.The fracture expansion under unloading conditions occurred due to tensile stress T caused by unloading differential rebound deformation and the shear stress on the fissure surface. 展开更多
关键词 Fracture damage Fissured coal Triaxial unloading Particle flow code
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Influence of unloading orifice size on the production of microsized ore particles by gas rapid unloading 认领 引用
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作者 Genghao Zhang Deyang Zhao +3 位作者 Yi Chang Yongbo Fan Renshu Yang Shihai Li 《International Journal of Minerals,Metallurgy and Materials》 SCIE EI CAS CSCD 2025年第10期2366-2375,共10页
Gas rapid unloading(GRU)is an innovative technology for ore comminution.Increasing the production of fine powder in each ore grinding cycle is vital for scaling up the GRU method to industrial applications.This study ... Gas rapid unloading(GRU)is an innovative technology for ore comminution.Increasing the production of fine powder in each ore grinding cycle is vital for scaling up the GRU method to industrial applications.This study utilizes laboratory experiments to demon-strate that moderately reducing the orifice size significantly enhances pulverization and increases fine particle yield.Numerical simulations suggest that smaller orifices improve pulverization by increasing jet speed,reducing pressure drop,and creating a larger pressure difference inside and outside the unloading orifice.The orifice size should be optimized based on feed size to ensure efficient ore discharge.Reducing the unloading orifice size improves GRU grinding efficiency and energy use,offering guidance for the design of ore discharge ports in future industrial-scale equipment. 展开更多
关键词 iron ore pulverization high-pressure gas rapid unloading orifice size high-pressure gas jets
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Experimental and numerical study on mechanical behavior of rock beam fracture under unloading with different thicknesses and spans in deep mining working face 认领 引用
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作者 SUN Xiao-ming JIANG Ming +1 位作者 ZHAO Wen-chao MIAO Cheng-yu 《Journal of Central South University》 SCIE EI CAS CSCD 2025年第7期2570-2592,共23页
The stability of the roof in coal mining is crucial for ensuring safe extraction.Studying the mechanical behavior of rock beams under various conditions is essential for improving coal mining safety.However,research o... The stability of the roof in coal mining is crucial for ensuring safe extraction.Studying the mechanical behavior of rock beams under various conditions is essential for improving coal mining safety.However,research on the dynamic response of rock beams under sudden unloading remains limited.This study utilized a self-developed bidirectional loading and unilateral unloading test system to simulate how sudden lower strata subsidence induces the fracture of upper hard rock beams.Bottom unloading experiments were performed on rock beams with varying thicknesses and spans.The experiments recorded surface crack development and internal damage evolution using high speed photography and acoustic emission monitoring.The results show that rock beams experience multiple stress reductions after unloading,with the largest reduction occurring in the first stage.Flexural deformation was observed,becoming more pronounced as the thickness-span ratio decreased.Greater thickness increased shear cracks and crack expansion angles,while larger spans promoted tensile cracks,arched crack formation,and notable rock spalling.Acoustic emission analysis showed that signal count and energy increased with thickness and span.Finally,discrete element numerical simulations revealed the critical controlling role of harder rock strata in rock beam failure:when the harder strata are at the top,cracks are sharp,and shear failure is more likely;when they are at the bottom,the overall failure range expands,and cracks tend to form arches.These findings improve the understanding of dynamic rock beam fracture under sudden unloading and offer theoretical guidance for roof stability control in deep mining. 展开更多
关键词 roof rock beam bottom unloading thickness and span tensile crack composite rock beam harder rock strata
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Shear properties of non-persistent coplanar fractured hard rocks under normal stress unloading 认领 引用
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作者 Guoqing Chen Liangjie Gu +2 位作者 Qiang Xu Xing Yang Yang Zhao 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2025年第6期3593-3608,共16页
During the excavation of large-scale rock slopes and deep hard rock engineering,the induced rapid unloading serves as the primary cause of rock mass deformation and failure.The essence of this phenomenon lies in the o... During the excavation of large-scale rock slopes and deep hard rock engineering,the induced rapid unloading serves as the primary cause of rock mass deformation and failure.The essence of this phenomenon lies in the opening-shear failure process triggered by the normal stress unloading of fractured rock mass.In this study,we focus on local-scale rock fracture and conduct direct shear tests under different normal stress unloading rates on five types of non-persistent fractured hard rocks.The aim is to analyze the influence of normal stress unloading rates on the failure modes and shear mechanical characteristics of non-persistent fractured rocks.The results indicate that the normal unloading displacement decreases gradually with increasing normal stress unloading rate,while the influence of normal stress unloading rate on shear displacement is not significant.As the normal stress unloading rate increases,the rocks brittle failure process accelerates,and the degree of rocks damage decreases.Analysis of the stress state on rock fracture surfaces reveals that increasing the normal stress unloading rate enhances the compressive stress on rocks,leading to a transition in the failure mode from shear failure to tensile failure.A negative exponential strength formula was proposed,which effectively fits the relationship between failure normal stress and normal stress unloading rate.The findings enrich the theoretical foundation of unloading rock mechanics and provide theoretical support for disasters prevention and control in rock engineering excavations. 展开更多
关键词 Shear properties Non-persistent coplanar fractures Normal stress unloading rate Hard rocks Acoustic emission(AE)
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Mechanical responses of sandstone exposed to triaxial differential cyclic loading with distinct unloading rates of confining stress:A lab scale investigation 认领 引用 被引量：2
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作者 Z.Y.Song W.H.Zhang +3 位作者 Z.Yu Y.Zhao M.Zhang W.G.Dang 《International Journal of Coal Science & Technology》 SCIE EI CAS CSCD 2025年第4期133-159,共27页
This article investigates the mechanical responses and acoustic emission(AE)characteristics of sandstone under the triaxial differential cyclic loading(DCL)at different unloading rates of confining stress.The test res... This article investigates the mechanical responses and acoustic emission(AE)characteristics of sandstone under the triaxial differential cyclic loading(DCL)at different unloading rates of confining stress.The test results indicate that strength of rock specimens under different stress paths of triaxial unloading confining stress-differential cyclic loading(TUCS-DCL)can be fitted by the Mohr–Coulomb,Hoek–Brown,and Bieniawski criteria.The confining stress unloading rate can dominate the radial strain rate,while the axial DCL pattern has an unpronounced effect.The confining stress unloading rate affects the energy evolution in radial and axial directions of specimens,with the ratio of radially released energy to axially consumed energy fluctuating more significantly during the fast unloading of confining stress,the valley value of the ratio can serve as a precursor for failure.The confining stress unloading rate has no significant effect on stress–strain phase shift,while axial rapid-loading-slow-unloading can correspond to a larger magnitude of phase shift.AE signals begin to significantly increase after the confining stress is unloaded to zero,and a notable Kaiser effect is observed during cyclic loading preceding the failure. 展开更多
关键词 Differential cyclic loading(DCL) Unloading rate Energy dissipation Phase shift Acoustic emission
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Granite strainbursts induced by true triaxial transient unloading at different stress levels:Insights from excess energy △E 认领 引用 被引量：2
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作者 Hongru Li Manchao He +3 位作者 Yingming Xiao Dongqiao Liu Jie Hu Tai Cheng 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2025年第11期7078-7092,共15页
In this study,based on the rockburst disaster mechanism of excess energy △E>0,true triaxial transient unloading strainburst(including instantaneous strainburst and delayed strainburst)experiments were performed on... In this study,based on the rockburst disaster mechanism of excess energy △E>0,true triaxial transient unloading strainburst(including instantaneous strainburst and delayed strainburst)experiments were performed on granite specimens at different maximum principal stress levels.The experimental results were then analyzed,with the strainburst characteristics and acoustic emission(AE)responses of the granite specimens being examined.The excess energy △E was derived through a comparison with the results of conventional biaxial compression tests.The following beneficial conclusions were drawn.The mechanical strength of delayed strainburst specimens initially increases and then decreases with the rise of the unloading stress level.In contrast,the mechanical strength of instantaneous strainburst specimens is higher than that of delayed ones,increasing with the unloading stress level.In terms of fragment ejection velocity and scale,the rockburst intensity of a specimen is positively correlated with its mechanical strength.A pronounced linear relationship exists between the excess energy △E and the fragment ejection velocity(as well as weight),indicating that △E is intimately linked to the kinetic energy of rockbursts.Rockbursts lead to the formation of burst pits and typical V-shaped damage zones near the free face of the specimens,within which tensile cracks dominate.Additionally,the distribution of AE AFRA values indicates that the proportion of tensile cracks increases with the rise of unloading stress level,suggesting that transient unloading under high stress levels significantly promotes tensile fracture.It is anticipated that this study will provide further elucidation on the mechanism of rockburst kinetic energy generation,thereby establishing a foundation for the design of rockburst support measures in engineering applications. 展开更多
关键词 Rockburst True triaxial unloading Excess energy Rock fragmentation Acoustic emission(AE)
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