It has become an inevitable trend of human development to seek resources from the deep underground.However,rock encountered in deep underground engineering is usually in an anisotropic stress state(σ_(1)>σ>σ_...It has become an inevitable trend of human development to seek resources from the deep underground.However,rock encountered in deep underground engineering is usually in an anisotropic stress state(σ_(1)>σ>σ_(3))due to the influences of geological structures and engineering disturbances.It is therefore essential to study the mechanical,seepage,and dynamic disaster behaviors of deep rock under true triaxial stress to ensure the safe operation of deep rock engineering and the efficient exploitation of deep resources.In recent years,experimental techniques and research on true triaxial rock mechanics have achieved fruitful results that have promoted the rapid development of deep rock mechanics;thus,it is necessary to systematically review and summarize these developments.This work first introduced several typical true triaxial testing apparatus and then reviewed the corresponding research progress on rock deformation,strength,failure mode,brittleness,and energy as well as the 3D volumetric fracturing(dynamic disaster)properties of deep rocks under true triaxial stress.Then,several commonly used true triaxial rock strength criteria and their applicability,the permeability characteristics and mathematical models of deep reservoir rocks,and the disaster-causing processes and mechanisms of disturbed volumetric fracturing(rockburst,compound dynamic disasters)in deep rock engineering were described.This work may provide an essential reference for addressing the true triaxial rock mechanics issues involved in deep rock engineering,especially regarding the stability of surrounding rock at depth,disaster prevention and control,and oil and gas exploitation.展开更多
Precisely understanding the dynamic mechanical properties and failure modes of rocks subjected to true triaxial stress state(σ1>σ2>σ3,whereσ1,σ2,andσ3 are the major principal stress,intermediate principal ...Precisely understanding the dynamic mechanical properties and failure modes of rocks subjected to true triaxial stress state(σ1>σ2>σ3,whereσ1,σ2,andσ3 are the major principal stress,intermediate principal stress,and minor principal stress,respectively)is essential to the safety of underground engineering.However,in the laboratory,it is difficult to maintain the constant true triaxial stress state of rocks during the dynamic testing process.Herein,a numerical servo triaxial Hopkinson bar(NSTHB)was developed to study the dynamic responses of rocks confronted with a true triaxial stress state,in which lateral stresses can maintain constant.The results indicate that the dynamic strength and elastic modulus of rocks increase with the rise of intermediate principal stressσ2,while the dynamic elastic modulus is independent of the dynamic strain rate.Simulated acoustic emission distributions indicate that the intermediate principal stressσ2 dramatically affects dynamic failure modes of triaxial confined rocks.Asσ2 increases,the failure pattern switches from a single diagonal shear zone into two parallel shear zones with a small slant.Moreover,a recent triaxial Hopkinson bar experimental system using three bar pairs is also numerically established,and the measuring discrepancies are identified between the two numerical bar systems.The proposed NSTHB system provides a controllable tool for studying the dynamic triaxial behavior of rocks.展开更多
As main part of underground rock mass,the three-dimensional(3D)morphology of natural fractures plays an important role in rock mass stability.Based on previous studies on 3D morphology,this study probes into the law a...As main part of underground rock mass,the three-dimensional(3D)morphology of natural fractures plays an important role in rock mass stability.Based on previous studies on 3D morphology,this study probes into the law and mechanism regarding the influence of the confining pressure constraints on 3D morphological features of natural fractures.First,fracture surfaces were obtained by true triaxial compression test and 3D laser scanning.Then 3D morphological parameters of fractures were calculated by using Grasselli’s model.The results show that the failure mode of granites developed by true triaxial stress can be categorized into tension failure and shear failure.Based on the spatial position of fractures,they can be divided into tension fracture surface,S-1 shear fracture surface,and S-2 shear fracture surface.Micro-failure of the tension fracture surface is dominated by mainly intergranular fracture;the maximum height of asperities on the fracture surface and the 3D roughness of fracture surfaces are influenced by σ_(3) only and they are greater than those of shear fracture surfaces,a lower overall uniformity than tension fracture surface.S-1 shear fracture surface and S-2 shear fracture surface are dominated by intragranular and intergranular coupling fracture.The maximum height of asperities on the fracture surface and 3D roughness of fracture surface are affected by σ_(1),σ_(2),and σ_(3).With the increase of σ_(2) or σ_(3),the cutting off of asperities on the fracture surface becomes more common,the maximum height of asperities and 3D roughness of fracture surface further decrease,and the overall uniformity gets further improved.The experimental results are favorable for selecting technical parameters of enhanced geothermal development and the safety of underground mine engineering.展开更多
As P-wave velocity is sensitive to the variations in coal reservoir parameters,it is possible to monitor the injected CO_(2)through P-wave velocity during CO_(2)sequestration in coal.However,the effects of CO_(2)on th...As P-wave velocity is sensitive to the variations in coal reservoir parameters,it is possible to monitor the injected CO_(2)through P-wave velocity during CO_(2)sequestration in coal.However,the effects of CO_(2)on the coal P-wave velocity under triaxial stress are not clearly discerned.In the present study,different boundary conditions and gases were utilised to investigate the factors affecting the P-wave velocity after the interaction of coal with CO_(2).Experiments with helium indicated that the pore pressure primarily affected the P-wave velocity by altering the effective stress.Experiments with CH4 and CO_(2)indicated that matrix swelling induced-cleats porosity decline significantly promoted P-wave velocity.Moreover,CO_(2)caused a wider scale and severe weakening of coal matrix than CH4,thereby significantly decreasing the P-wave velocity,and the decline in P-wave velocity increases with vitrinite content.Furthermore,experiments under different boundary conditions showed that with the boundary condition having more constraints,the decrement of pore pressure on P-wave velocity is more weaken,whereas the improvement of matrix swelling on P-wave velocity is more evident.This study contributes to understanding the mechanism of effect of CO_(2)on P-wave velocity under triaxial stress condition and provides guidance for monitoring CO_(2)sequestration in coal.展开更多
To more accurately describe the coal damage and fracture evolution law during liquid nitrogen(LN_(2))fracturing under true triaxial stress,a thermal-hydraulic-mechanical-damage(THMD)coupling model for LN_(2) fracturin...To more accurately describe the coal damage and fracture evolution law during liquid nitrogen(LN_(2))fracturing under true triaxial stress,a thermal-hydraulic-mechanical-damage(THMD)coupling model for LN_(2) fracturing coal was developed,considering the coal heterogeneity and thermophysical parameters of nitrogen.The accuracy and applicability of model were verified by comparing with LN_(2) injection pre-cooling and fracturing experimental data.The effects of different pre-cooling times and horizontal stress ratios on coal damage evolution,permeability,temperature distribution,and fracture characteristics were analyzed.The results show that the permeability and damage of the coal increase exponentially,while the temperature decreases exponentially during the fracturing process.As the pre-cooling time increases,the damage range of the coal expands,and the fracture propagation becomes more pronounced.The initiation pressure and rupture pressure decrease and tend to stabilize with longer precooling times.As the horizontal stress ratio increases,fractures preferentially extend along the direction of maximum horizontal principal stress,leading to a significant decrease in both initiation and rupture pressures.At a horizontal stress ratio of 3,the initiation pressure drops by 48.07%,and the rupture pressure decreases by 41.36%.The results provide a theoretical basis for optimizing LN_(2) fracturing techniques and improving coal seam modification.展开更多
Both bulk stress(σ_(i i))and stress path(SP)significantly affect the transportation characteristics of deep gas during reservoir pressure depletion.Therefore,the experimental study of horizontal stress unloading on s...Both bulk stress(σ_(i i))and stress path(SP)significantly affect the transportation characteristics of deep gas during reservoir pressure depletion.Therefore,the experimental study of horizontal stress unloading on seepage behavior of gas-bearing coal under constantσi i-constraints is performed.The results show that coal permeability is affected by horizontal stress anisotropy(σ_(H)≠σh),and the contribution of minor horizontal stress to permeability is related to the differential response of horizontal strain.The slippage phenomenon is prominent in deep high-stress regime,especially in low reservoir pressure.σ_(i i)and SP jointly determine the manifestation of slippage effect and the strength of stress sensitivity(γ)of permeability.Deep reservoir implies an incremental percentage of slip-based permeability,and SP weakens the slippage effect by changing the elastic–plastic state of coal.However,γis negatively correlated with slippage effect.From the Walsh model,narrow(low aspect-ratio)fractures within the coal under unloading SP became the main channel for gas seepage,and bring the effective stress coefficient of permeability(χ)less than 1 for both low-stress elastic and high-stress damaged coal.With the raise of the effective stress,the effect of pore-lined clay particles on permeability was enhanced,inducing an increase inχfor highstress elastic coal.展开更多
针对西安某地铁车站基坑Q3原状黄土,开展偏应力恒定的循环球应力加/卸载试验,对不同固结应力与不同动应力幅值条件下原状黄土的轴向变形与体应变发展规律进行分析。结果表明:循环球应力作用下,黄土会产生一定的不可逆塑性变形与可逆弹...针对西安某地铁车站基坑Q3原状黄土,开展偏应力恒定的循环球应力加/卸载试验,对不同固结应力与不同动应力幅值条件下原状黄土的轴向变形与体应变发展规律进行分析。结果表明:循环球应力作用下,黄土会产生一定的不可逆塑性变形与可逆弹性变形,其变形增长规律与偏压程度和动应力幅值成正比,与固结应力成反比;轴向变形规律符合Monismith C L幂函数模型,且其模型参数与固结应力条件具有显著的相关性;原状黄土在加载初期体应变累积较明显,之后逐渐趋于稳定;固结应力比对体应变影响较小,固结球应力对体应变发展具有抑制作用,表明浅层土体更容易产生压缩变形。展开更多
基金This research was supported by the National Natural Science Foundation of China(No.52104209)the Postdoctoral Research Foundation of China(No.2021M692192)+1 种基金the National Natural Science Foundation of China(Nos.51827901 and 52174082)the Program for Guangdong Introducing Innovative and Entrepre-neurial Teams(No.2019ZT08G315).
文摘It has become an inevitable trend of human development to seek resources from the deep underground.However,rock encountered in deep underground engineering is usually in an anisotropic stress state(σ_(1)>σ>σ_(3))due to the influences of geological structures and engineering disturbances.It is therefore essential to study the mechanical,seepage,and dynamic disaster behaviors of deep rock under true triaxial stress to ensure the safe operation of deep rock engineering and the efficient exploitation of deep resources.In recent years,experimental techniques and research on true triaxial rock mechanics have achieved fruitful results that have promoted the rapid development of deep rock mechanics;thus,it is necessary to systematically review and summarize these developments.This work first introduced several typical true triaxial testing apparatus and then reviewed the corresponding research progress on rock deformation,strength,failure mode,brittleness,and energy as well as the 3D volumetric fracturing(dynamic disaster)properties of deep rocks under true triaxial stress.Then,several commonly used true triaxial rock strength criteria and their applicability,the permeability characteristics and mathematical models of deep reservoir rocks,and the disaster-causing processes and mechanisms of disturbed volumetric fracturing(rockburst,compound dynamic disasters)in deep rock engineering were described.This work may provide an essential reference for addressing the true triaxial rock mechanics issues involved in deep rock engineering,especially regarding the stability of surrounding rock at depth,disaster prevention and control,and oil and gas exploitation.
基金the financial support from the National Natural Science Foundation of China(Nos.52039007 and 52009086)the Sichuan Province Youth Science and Technology Innovation Team(No.2020JDTD0001)。
文摘Precisely understanding the dynamic mechanical properties and failure modes of rocks subjected to true triaxial stress state(σ1>σ2>σ3,whereσ1,σ2,andσ3 are the major principal stress,intermediate principal stress,and minor principal stress,respectively)is essential to the safety of underground engineering.However,in the laboratory,it is difficult to maintain the constant true triaxial stress state of rocks during the dynamic testing process.Herein,a numerical servo triaxial Hopkinson bar(NSTHB)was developed to study the dynamic responses of rocks confronted with a true triaxial stress state,in which lateral stresses can maintain constant.The results indicate that the dynamic strength and elastic modulus of rocks increase with the rise of intermediate principal stressσ2,while the dynamic elastic modulus is independent of the dynamic strain rate.Simulated acoustic emission distributions indicate that the intermediate principal stressσ2 dramatically affects dynamic failure modes of triaxial confined rocks.Asσ2 increases,the failure pattern switches from a single diagonal shear zone into two parallel shear zones with a small slant.Moreover,a recent triaxial Hopkinson bar experimental system using three bar pairs is also numerically established,and the measuring discrepancies are identified between the two numerical bar systems.The proposed NSTHB system provides a controllable tool for studying the dynamic triaxial behavior of rocks.
基金support from the National Natural Science Foundation of China(Nos.51974173 and 52004147)the Natural Science Foundation of Shandong Province(Nos.ZR2020QD122 and ZR2020QE129).
文摘As main part of underground rock mass,the three-dimensional(3D)morphology of natural fractures plays an important role in rock mass stability.Based on previous studies on 3D morphology,this study probes into the law and mechanism regarding the influence of the confining pressure constraints on 3D morphological features of natural fractures.First,fracture surfaces were obtained by true triaxial compression test and 3D laser scanning.Then 3D morphological parameters of fractures were calculated by using Grasselli’s model.The results show that the failure mode of granites developed by true triaxial stress can be categorized into tension failure and shear failure.Based on the spatial position of fractures,they can be divided into tension fracture surface,S-1 shear fracture surface,and S-2 shear fracture surface.Micro-failure of the tension fracture surface is dominated by mainly intergranular fracture;the maximum height of asperities on the fracture surface and the 3D roughness of fracture surfaces are influenced by σ_(3) only and they are greater than those of shear fracture surfaces,a lower overall uniformity than tension fracture surface.S-1 shear fracture surface and S-2 shear fracture surface are dominated by intragranular and intergranular coupling fracture.The maximum height of asperities on the fracture surface and 3D roughness of fracture surface are affected by σ_(1),σ_(2),and σ_(3).With the increase of σ_(2) or σ_(3),the cutting off of asperities on the fracture surface becomes more common,the maximum height of asperities and 3D roughness of fracture surface further decrease,and the overall uniformity gets further improved.The experimental results are favorable for selecting technical parameters of enhanced geothermal development and the safety of underground mine engineering.
基金supported by the National Natural Science Foundation of China(No.51974304)the Natural Science Foundation of Hebei Province(No.E2020402075)+2 种基金the 2nd Xplorer Prize sponsored by the Tencent Foundationthe Program for Changjiang Scholars and Innovative Research Team in University(No.IRT 17R103)the Qinglan Project of Jiangsu Province.
文摘As P-wave velocity is sensitive to the variations in coal reservoir parameters,it is possible to monitor the injected CO_(2)through P-wave velocity during CO_(2)sequestration in coal.However,the effects of CO_(2)on the coal P-wave velocity under triaxial stress are not clearly discerned.In the present study,different boundary conditions and gases were utilised to investigate the factors affecting the P-wave velocity after the interaction of coal with CO_(2).Experiments with helium indicated that the pore pressure primarily affected the P-wave velocity by altering the effective stress.Experiments with CH4 and CO_(2)indicated that matrix swelling induced-cleats porosity decline significantly promoted P-wave velocity.Moreover,CO_(2)caused a wider scale and severe weakening of coal matrix than CH4,thereby significantly decreasing the P-wave velocity,and the decline in P-wave velocity increases with vitrinite content.Furthermore,experiments under different boundary conditions showed that with the boundary condition having more constraints,the decrement of pore pressure on P-wave velocity is more weaken,whereas the improvement of matrix swelling on P-wave velocity is more evident.This study contributes to understanding the mechanism of effect of CO_(2)on P-wave velocity under triaxial stress condition and provides guidance for monitoring CO_(2)sequestration in coal.
基金financially supported by the National Natural Science Foundation of China(Nos.51874236 and 52174207)Shaanxi Science and Technology Innovation Team(No.2022TD02)Henan University of Science and Technology PhD Funded Projects(No.B2025-9)。
文摘To more accurately describe the coal damage and fracture evolution law during liquid nitrogen(LN_(2))fracturing under true triaxial stress,a thermal-hydraulic-mechanical-damage(THMD)coupling model for LN_(2) fracturing coal was developed,considering the coal heterogeneity and thermophysical parameters of nitrogen.The accuracy and applicability of model were verified by comparing with LN_(2) injection pre-cooling and fracturing experimental data.The effects of different pre-cooling times and horizontal stress ratios on coal damage evolution,permeability,temperature distribution,and fracture characteristics were analyzed.The results show that the permeability and damage of the coal increase exponentially,while the temperature decreases exponentially during the fracturing process.As the pre-cooling time increases,the damage range of the coal expands,and the fracture propagation becomes more pronounced.The initiation pressure and rupture pressure decrease and tend to stabilize with longer precooling times.As the horizontal stress ratio increases,fractures preferentially extend along the direction of maximum horizontal principal stress,leading to a significant decrease in both initiation and rupture pressures.At a horizontal stress ratio of 3,the initiation pressure drops by 48.07%,and the rupture pressure decreases by 41.36%.The results provide a theoretical basis for optimizing LN_(2) fracturing techniques and improving coal seam modification.
基金financially supported by the National Natural Science Foundation of China(Nos.52304265,52174216,and 52274145)the Natural Science Foundation of Jiangsu Province(No.BK20221121)the State Key Laboratory of Mining Disaster Prevention and Control(Shandong University of Science and Technology)and Ministry of Education(No.JMDPC202301)。
文摘Both bulk stress(σ_(i i))and stress path(SP)significantly affect the transportation characteristics of deep gas during reservoir pressure depletion.Therefore,the experimental study of horizontal stress unloading on seepage behavior of gas-bearing coal under constantσi i-constraints is performed.The results show that coal permeability is affected by horizontal stress anisotropy(σ_(H)≠σh),and the contribution of minor horizontal stress to permeability is related to the differential response of horizontal strain.The slippage phenomenon is prominent in deep high-stress regime,especially in low reservoir pressure.σ_(i i)and SP jointly determine the manifestation of slippage effect and the strength of stress sensitivity(γ)of permeability.Deep reservoir implies an incremental percentage of slip-based permeability,and SP weakens the slippage effect by changing the elastic–plastic state of coal.However,γis negatively correlated with slippage effect.From the Walsh model,narrow(low aspect-ratio)fractures within the coal under unloading SP became the main channel for gas seepage,and bring the effective stress coefficient of permeability(χ)less than 1 for both low-stress elastic and high-stress damaged coal.With the raise of the effective stress,the effect of pore-lined clay particles on permeability was enhanced,inducing an increase inχfor highstress elastic coal.
文摘煤的层理面倾角(bedding plane angle,BPA)对射流破岩的效果影响显著。为探讨真三轴应力下不同BPA煤的射流破坏机制,开展了不同BPA煤在真三轴应力下的纯水射流冲蚀试验。结果表明,当煤的BPA较低或较高时,射流冲击分别容易形成锥形破碎坑和裂缝坑,破碎坑开口随着BPA的增大由圆形逐步向椭圆形过渡,煤的破坏模式由剪切破坏主导转变为拉伸-水楔效应主导。随着BPA增至60°,破岩体积增加了154.35%。当施加三轴应力时,煤层理面对射流破煤性能的影响被抑制,不同BPA煤的破坏模式仅呈现圆孔破碎坑,水锤压力引起的剪切破坏是煤在三轴应力下破坏的主要原因,60°BPA煤样的破坏体积减少了95.60%,相比其他倾角降低幅度达到最大。BPA对煤的轴向损伤演化具有驱动作用,随着倾角增大,轴向损伤发生波动。当施加三轴应力时,三轴应力抑制了射流破煤的损伤演化,煤的轴向损伤出现收缩。煤的破碎坑壁面的扫描电子显微镜(scanning electron microscope,SEM)结果表明:当施加三轴应力时,0°BPA煤样的破碎孔壁不再出现微裂隙与脆性剪切破坏的痕迹,并且孔隙的数量与尺寸大幅减小;60°BPA煤样的破碎孔壁不再出现水楔作用导致的大量锯齿状痕迹,三轴应力下不同BPA煤的破碎孔壁面均出现明显的延性剪切破坏特征。
文摘针对西安某地铁车站基坑Q3原状黄土,开展偏应力恒定的循环球应力加/卸载试验,对不同固结应力与不同动应力幅值条件下原状黄土的轴向变形与体应变发展规律进行分析。结果表明:循环球应力作用下,黄土会产生一定的不可逆塑性变形与可逆弹性变形,其变形增长规律与偏压程度和动应力幅值成正比,与固结应力成反比;轴向变形规律符合Monismith C L幂函数模型,且其模型参数与固结应力条件具有显著的相关性;原状黄土在加载初期体应变累积较明显,之后逐渐趋于稳定;固结应力比对体应变影响较小,固结球应力对体应变发展具有抑制作用,表明浅层土体更容易产生压缩变形。
