Using cemented rockfill to replace coal pillars offers an effective solution for reducing solid waste while ensuring the safety of gob-side entries.However,achieving the balance among low cost,high waste recycling rat...Using cemented rockfill to replace coal pillars offers an effective solution for reducing solid waste while ensuring the safety of gob-side entries.However,achieving the balance among low cost,high waste recycling rates,and adequate strength remains a significant challenge for cemented rockfill.This study used a composite alkali activator to activate gangue cemented rockfill.The compressive strength,scanning electron microscopy,energy dispersive spectrometer,mercury intrusion porosimetry,X-ray diffraction,and thermogra-vimetric tests were carried out to investigate the effect of the composite alkali activator proportion on the compressive strength,micro-structure,and composition of the cemented rockfill.The calcium silicate hydrate(C–S–H)molecular model of cemented rockfill was con-structed to explore the fracture evolution of the nucleated molecular structure under tension.The results show that compressive strength initially increased and then decreased with the activator proportion,the optimal activator proportion of 1:2 resulted in a 31.25%increase in strength at 3 d.This reasonable activator proportion strengthens the pozzolanic effect of gangue,and consumes more calcium hydroxide to inhibit its agglomeration,ultimately achieving the densification of microstructure.The activator proportion inevitably substitutes calcium ions with sodium ions in the C–S–H molecular model.The 12%substitution of calcium ions increases the adhesion between silicon chain layers,which is beneficial to the interlayer stress transfer.This work proposes a method for preparing low-cost cemented rockfill from al-kali-activated gangue,which can be used for solid waste recycling and reducing cement consumption to achieve low-carbon goals.展开更多
The mechanical behavior of cemented gangue backfill materials(CGBMs)is closely related to particle size distribution(PSD)of aggregates and properties of cementitious materials.Consequently,the true triaxial compressio...The mechanical behavior of cemented gangue backfill materials(CGBMs)is closely related to particle size distribution(PSD)of aggregates and properties of cementitious materials.Consequently,the true triaxial compression tests,CT scanning,SEM,and EDS tests were conducted on cemented gangue backfill samples(CGBSs)with various carbon nanotube concentrations(P_(CNT))that satisfied fractal theory for the PSD of aggregates.The mechanical properties,energy dissipations,and failure mechanisms of the CGBSs under true triaxial compression were systematically analyzed.The results indicate that appropriate carbon nanotubes(CNTs)effectively enhance the mechanical properties and energy dissipations of CGBSs through micropore filling and microcrack bridging,and the optimal effect appears at P_(CNT)of 0.08wt%.Taking PSD fractal dimension(D)of 2.500 as an example,compared to that of CGBS without CNT,the peak strength(σ_(p)),axial peak strain(ε_(1,p)),elastic strain energy(Ue),and dissipated energy(U_(d))increased by 12.76%,29.60%,19.05%,and90.39%,respectively.However,excessive CNTs can reduce the mechanical properties of CGBSs due to CNT agglomeration,manifesting a decrease inρ_(p),ε_(1,p),and the volumetric strain increment(Δε_(v))when P_(CNT)increases from 0.08wt%to 0.12wt%.Moreover,the addition of CNTs improved the integrity of CGBS after macroscopic failure,and crack extension in CGBSs appeared in two modes:detour and pass through the aggregates.Theσ_(p)and U_(d)firstly increase and then decrease with increasing D,and porosity shows the opposite trend.Theε_(1,p)andΔε_(v)are negatively correlated with D,and CGBS with D=2.150 has the maximum deformation parameters(ε_(1,p)=0.05079,Δε_(v)=0.01990)due to the frictional slip effect caused by coarse aggregates.With increasing D,the failure modes of CGBSs are sequentially manifested as oblique shear failure,"Y-shaped"shear failure,and conjugate shear failure.展开更多
To address the dual challenges of resource utilization of mining solid waste(e.g.,coal gangue)and performance enhancement of cemented rockfill,this study systematically investigates the mechanisms of ultrasonic disper...To address the dual challenges of resource utilization of mining solid waste(e.g.,coal gangue)and performance enhancement of cemented rockfill,this study systematically investigates the mechanisms of ultrasonic dispersion time and polycarboxylate superplasti-cizer(PCE)on the properties of cellulose nanofiber(CNF)-modified cemented rockfill.A series of comparative experiments were de-signed with varying ultrasonic dispersion times(0-60 min)and PCE dosages(0.1wt%-0.4wt%).Through mechanical testing,hydration product analysis,and microstructural characterization,the study revealed the advantages of PCE in promoting CNF dispersion to enhance the engineering applicability of cemented rockfill.The results demonstrate that:(1)Ultrasonic dispersion for 30 min increases the com-pressive strength by 37.7%compared to the untreated group;however,excessive ultrasonication(60 min)induces hydrolysis of CNF,re-leasing reducing sugars that retard hydration.(2)PCE facilitates CNF dispersion,achieving a 29.1%increase in compressive strength at a dosage of 0.4wt%,while simultaneously improving hydration products and microstructural development.(3)While ultrasonic dispersion yields slightly higher strength improvements,PCE demonstrates superior cost-effectiveness and operational convenience,rendering it more viable for industrial adoption.This study provides a theoretical foundation for the nano-enhanced modification of cemented rockfill,offering new insights into the recycling of solid waste and the development of high-performance materials.展开更多
Massive fracturing fluid injection in reservoir stimulation can alter the fluid pressure field,potentially inducing the faults to slip in an aseismic or seismic phenomenon.In this work,laboratory friction experiments ...Massive fracturing fluid injection in reservoir stimulation can alter the fluid pressure field,potentially inducing the faults to slip in an aseismic or seismic phenomenon.In this work,laboratory friction experiments were performed on split-cutting granite fracture to investigate the effect of fluid pressure on injection-induced slip behavior.The injection experiments spanned a fluid pressure range of 1-20 MPa,which was up to half of the confining pressure.The laboratory results demonstrated that an increase in confining pressure led to a marginal reduction in the friction coefficient,decreasing from a range of 0.70-0.80 at 10 MPa to 0.71-0.75 at 40 MPa.Friction constitutive parameters in experiments with fluid pressure above 10 MPa exhibited a transition from velocity-strengthening to velocity-weakening behavior,while remaining consistently velocity-strengthening below this threshold.Similarly,measurements of dilatancy and critical slip distance exhibited a similar evolution,first increasing and then becoming approximately constant,independent of fluid pressure.The observed microstructural evolution of the split-cutting fractures during slip testing supported these mechanical responses.Post-shear slip,a decrease in the fracture roughness and asperity distribution of the split-cutting fracture was noted,with the decrease in amplitude being more pronounced at high confining pressure.Research may provide a prospect on slip-on faults with fluid pressure.展开更多
Gaomiaozi(GMZ)bentonite is a potential buffer/backfill material for a deep geological disposal of highlevel radioactive waste.It has a wide pore size distribution(PSD)with sizes ranging from several nanometers to more...Gaomiaozi(GMZ)bentonite is a potential buffer/backfill material for a deep geological disposal of highlevel radioactive waste.It has a wide pore size distribution(PSD)with sizes ranging from several nanometers to more than one hundred microns.Thus,properly characterizing the pore structures of GMZ bentonite is a challenging issue.In this study,pressure-controlled porosimetry(PCP),ratecontrolled porosimetry(RCP),and scanning electron microscopy(SEM)were used to investigate the PSD of GMZ bentonite,The results indicate that each method has its limitation,and a combined use of PCP and RCP is suitable to obtain the full-scale PSD of GMZ bentonite.Moreover,we also compared the full-scale PSD with nuclear magnetic resonance(NMR)result.It is found that there is no significant difference in the range of PSD characterization between NMR and mercury intrusion method(PCP and RCP).However,in a ce rtain range,the detection accuracy of NMR is higher than that of mercury injection method.Finally,permeability prediction based on PCP and SEM data was conducted,and both of the two methods were found to be able to predict the permeability.The combined method is effective to obtain the full-scale PSD of GMZ bentonite,which is the key to estimation of the sealing ability of bentonite buffer.展开更多
Bulking characteristics of gangue are of great significance for the stability of goafs in mining overburden in the caving zones.In this paper,a particle discrete element method with clusters to represent gangue was ad...Bulking characteristics of gangue are of great significance for the stability of goafs in mining overburden in the caving zones.In this paper,a particle discrete element method with clusters to represent gangue was adopted to explore the bulking coefficient time effect of the broken rock in the caving zone under three-dimensional triaxial compression condition.The phenomena of stress corrosion,deformation,and failure of rock blocks were simulated in the numerical model.Meanwhile,a new criterion of rock fragments damage was put forward.It was found that the broken rock has obvious viscoelastic properties.A new equation based on the Burgers creep model was proposed to predict the bulking coefficient of broken rock.A deformation characteristic parameter of the prediction equation was analyzed,which can be set as a fixed value in the mid-and long-term prediction of the bulking coefficient.There are quadratic function relationships between the deformation characteristic parameter value and Talbot gradation index,axial pressure and confining pressure.展开更多
The interaction mechanism between coal and rock masses with supporting materials is significant in roadway control, especially in deep underground mining situations where dynamic hazards frequently happened due to hig...The interaction mechanism between coal and rock masses with supporting materials is significant in roadway control, especially in deep underground mining situations where dynamic hazards frequently happened due to high geo-stress and strong disturbed effects. This paper is to investigate the strain energy evolution in the interaction between coal and rock masses with self-designed energy-absorbing props and rock bolts by numerical modeling with the finite difference method. The interaction between rock and rock bolt/prop is accomplished by the cables element and the interface between the inner and outer props. Roadway excavation and coal extraction conditions in deep mining are numerically employed to investigate deformation, plastic zone ranges, strain energy input, accumulation, dissipation,and release. The effect on strain energy input, accumulation, dissipation, and release with rock deformation, and the plastic zone is addressed. A ratio of strain energy accumulation, dissipation, and release with energy input a, β, γ is to assess the dynamic hazards. The effects on roadway excavation and coal extraction steps of a, β, γ are discussed. The results show that:(1) In deep high geo-stress roadways, the energyabsorbing support system plays a dual role in resisting deformation and reducing the scope of plastic zones in surrounding rock, as well as absorbing energy release in the surrounding rock, especially in the coal extraction state to mitigate disturbed effects.(2) The strain energy input, accumulation is dependent on roadway deformation, the strain energy dissipation is relied on plastic zone area and disturbed effects, and strain energy release density is the difference among the three. The function of energyabsorbing rock bolts and props play a key role to mitigate strain energy release density and amount, especially in coal extraction condition, with a peak density value from 4×10^(4) to 1×10^(4)J/m^(3), and amount value from 3.57×10^(8) to 1.90×10^(6)J.(3) When mining is advanced in small steps, the strain energy accumulation is dominated. While in a large step, the released energy is dominant, thus a more dynamic hazards proneness. The energy-absorbing rock bolt and prop can reduce three times strain energy release amount, thus reducing the dynamic hazards. The results suggest that energy-absorbing props and rock bolts can effectively reduce the strain energy in the coal and rock masses, and prevent rock bursts and other hazards.The numerical model developed in this study can also be used to optimize the design of energyabsorbing props and rock bolts for specific mining conditions.展开更多
Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted r...Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted regarding various initial normal stresses(1e7 MPa)and numbers of shearing cycles(1 e5).The peak shear stress of fractures decreased with shear cycles due to progressively smooth surface morphologies,while increased with both JRC and initial normal stress and could be verified using the nonlinear Barton-Bandis failure criterion.The joint friction angle of fractures exponentially increased by 62.22%e64.87%with JRC while decreased by 22.1%e24.85%with shearing cycles.After unloading normal stress,the sliding initiation time of fractures increased with both JRC and initial normal stress due to more tortuous fracture morphologies and enhanced shearing resistance capacity.The surface resistance index(SRI)of fractures decreased by 4.35%e32.02%with increasing shearing cycles due to a more significant reduction of sliding initiation shear stress than that for sliding initiation normal stress,but increased by a factor of 0.41e1.64 with JRC.After sliding initiation,the shear displacement of fractures showed an increase in power function.By defining a sliding rate threshold of 5105 m/s,transition from“quasi-static”to“dynamic”sliding of fractures was identified,and the increase of sliding acceleration steepened with JRC while slowed down with shearing cycles.The normal displacement experienced a slight increase before shear sliding due to deformation recovery as the unloading stress was unloaded,and then enhanced shear dilation after sliding initiation due to climbing effects of surface asperities.Dilation was positively related to the shear sliding velocity of fractures.Wear characteristics of the fracture surfaces after shearing failure were evaluated using binary calculation,indicating an increasing shear area ratio by 45.24%e91.02%with normal stress.展开更多
Underground pumped storage power plant(UPSP)is an innovative concept for space recycling of abandoned mines.Its realization requires better understanding of the dynamic performance and durability of reservoir rock.Thi...Underground pumped storage power plant(UPSP)is an innovative concept for space recycling of abandoned mines.Its realization requires better understanding of the dynamic performance and durability of reservoir rock.This paper conducted ultrasonic detection,split Hopkinson pressure bar(SHPB)impact,mercury intrusion porosimetry(MIP),and backscatter electron observation(BSE)tests to investigate the dynamical behaviour and microstructure of sandstone with cyclical dry-wet damage.A coupling FEM-DEM model was constructed for reappearing mesoscopic structure damage.The results show that dry-wet cycles decrease the dynamic compressive strength(DCS)with a maximum reduction of 39.40%,the elastic limit strength is reduced from 41.75 to 25.62 MPa.The sieved fragments obtain the highest crack growth rate during the 23rd dry-wet cycle with a predictable life of 25 cycles for each rock particle.The pore fractal features of the macropores and micro-meso pores show great differences between the early and late cycles,which verifies the computational statistics analysis of particle deterioration.The numerical results show that the failure patterns are governed by the strain in pre-peak stage and the shear cracks are dominant.The dry-wet cycles reduce the energy transfer efficiency and lead to the discretization of force chain and crack fields.展开更多
The sealing performance of a bentonite barrier is highly dependent on its seepage characteristics, which are directly related to the characteristics of its pore structure. Based on scanning electron microscopy(SEM) an...The sealing performance of a bentonite barrier is highly dependent on its seepage characteristics, which are directly related to the characteristics of its pore structure. Based on scanning electron microscopy(SEM) and focused ion beam-SEM(FIB-SEM), the pore structure of bentonite was characterized at different scales. First, a reasonable gray threshold was determined through back analysis, and the image was binarized based on the threshold. In addition, binary images were used to analyze bentonite’s pore structure(porosity and pore size distribution). Furthermore, the effects of different algorithms on the pore structure characterization were evaluated. Then, permeability calculations were performed based on the previous pore structure characteristics and a modified permeability prediction model. For permeability prediction based on the three-dimensional model, the effect of pore tortuosity was also considered. Finally, the accuracy of numerical calculations was verified by conducting macroscopic gas and alcohol permeability experiments. This approach provides a better understanding of the microscale mechanism of gas transport in bentonite and the importance of pore structures at different scales in determining its seepage characteristics.展开更多
基金supported by the Key Research and Development Special Tasks of Xinjiang,China (No.2022B01051-2)the National Natural Science Foundation of China (Nos.U23B2091,42372328,and 52478253)+1 种基金the Natural Science Foundation of Jiangsu Province,China (No.BK20240209)the Science and Technology Program Special Fund of Jiangsu Province (Frontier Leading Technology Basic Research) Major projects,China (No.BK 20222004)
文摘Using cemented rockfill to replace coal pillars offers an effective solution for reducing solid waste while ensuring the safety of gob-side entries.However,achieving the balance among low cost,high waste recycling rates,and adequate strength remains a significant challenge for cemented rockfill.This study used a composite alkali activator to activate gangue cemented rockfill.The compressive strength,scanning electron microscopy,energy dispersive spectrometer,mercury intrusion porosimetry,X-ray diffraction,and thermogra-vimetric tests were carried out to investigate the effect of the composite alkali activator proportion on the compressive strength,micro-structure,and composition of the cemented rockfill.The calcium silicate hydrate(C–S–H)molecular model of cemented rockfill was con-structed to explore the fracture evolution of the nucleated molecular structure under tension.The results show that compressive strength initially increased and then decreased with the activator proportion,the optimal activator proportion of 1:2 resulted in a 31.25%increase in strength at 3 d.This reasonable activator proportion strengthens the pozzolanic effect of gangue,and consumes more calcium hydroxide to inhibit its agglomeration,ultimately achieving the densification of microstructure.The activator proportion inevitably substitutes calcium ions with sodium ions in the C–S–H molecular model.The 12%substitution of calcium ions increases the adhesion between silicon chain layers,which is beneficial to the interlayer stress transfer.This work proposes a method for preparing low-cost cemented rockfill from al-kali-activated gangue,which can be used for solid waste recycling and reducing cement consumption to achieve low-carbon goals.
基金financially supported by the National Natural Science Foundation of China(Nos.52174092,51904290,and 52374147)the Natural Science Foundation of Jiangsu Province,China(No.BK20220157)+2 种基金the Fundamental Research Funds for the Central Universities,China(No.2022YCPY0202)the National Key Research and Development Program of China(No.2023YFC3804204)the Major Program of Xinjiang Uygur Autonomous Region S cience and Technology(No.2023A01002)。
文摘The mechanical behavior of cemented gangue backfill materials(CGBMs)is closely related to particle size distribution(PSD)of aggregates and properties of cementitious materials.Consequently,the true triaxial compression tests,CT scanning,SEM,and EDS tests were conducted on cemented gangue backfill samples(CGBSs)with various carbon nanotube concentrations(P_(CNT))that satisfied fractal theory for the PSD of aggregates.The mechanical properties,energy dissipations,and failure mechanisms of the CGBSs under true triaxial compression were systematically analyzed.The results indicate that appropriate carbon nanotubes(CNTs)effectively enhance the mechanical properties and energy dissipations of CGBSs through micropore filling and microcrack bridging,and the optimal effect appears at P_(CNT)of 0.08wt%.Taking PSD fractal dimension(D)of 2.500 as an example,compared to that of CGBS without CNT,the peak strength(σ_(p)),axial peak strain(ε_(1,p)),elastic strain energy(Ue),and dissipated energy(U_(d))increased by 12.76%,29.60%,19.05%,and90.39%,respectively.However,excessive CNTs can reduce the mechanical properties of CGBSs due to CNT agglomeration,manifesting a decrease inρ_(p),ε_(1,p),and the volumetric strain increment(Δε_(v))when P_(CNT)increases from 0.08wt%to 0.12wt%.Moreover,the addition of CNTs improved the integrity of CGBS after macroscopic failure,and crack extension in CGBSs appeared in two modes:detour and pass through the aggregates.Theσ_(p)and U_(d)firstly increase and then decrease with increasing D,and porosity shows the opposite trend.Theε_(1,p)andΔε_(v)are negatively correlated with D,and CGBS with D=2.150 has the maximum deformation parameters(ε_(1,p)=0.05079,Δε_(v)=0.01990)due to the frictional slip effect caused by coarse aggregates.With increasing D,the failure modes of CGBSs are sequentially manifested as oblique shear failure,"Y-shaped"shear failure,and conjugate shear failure.
基金support from the National Natural Science Foundation of China(Nos.42372328,U23B2091,52478253,and 52374147)Natural Science Foundation of Jiangsu Province,China(No.BK20240209).
文摘To address the dual challenges of resource utilization of mining solid waste(e.g.,coal gangue)and performance enhancement of cemented rockfill,this study systematically investigates the mechanisms of ultrasonic dispersion time and polycarboxylate superplasti-cizer(PCE)on the properties of cellulose nanofiber(CNF)-modified cemented rockfill.A series of comparative experiments were de-signed with varying ultrasonic dispersion times(0-60 min)and PCE dosages(0.1wt%-0.4wt%).Through mechanical testing,hydration product analysis,and microstructural characterization,the study revealed the advantages of PCE in promoting CNF dispersion to enhance the engineering applicability of cemented rockfill.The results demonstrate that:(1)Ultrasonic dispersion for 30 min increases the com-pressive strength by 37.7%compared to the untreated group;however,excessive ultrasonication(60 min)induces hydrolysis of CNF,re-leasing reducing sugars that retard hydration.(2)PCE facilitates CNF dispersion,achieving a 29.1%increase in compressive strength at a dosage of 0.4wt%,while simultaneously improving hydration products and microstructural development.(3)While ultrasonic dispersion yields slightly higher strength improvements,PCE demonstrates superior cost-effectiveness and operational convenience,rendering it more viable for industrial adoption.This study provides a theoretical foundation for the nano-enhanced modification of cemented rockfill,offering new insights into the recycling of solid waste and the development of high-performance materials.
基金funded by the National Key Research and Development Program of China(Grant No.2023YFC3804205)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant No.KYCX24_2706)the Graduate Innovation Program of China University of Mining and Technology(Grant No.2024WLKXJ203).
文摘Massive fracturing fluid injection in reservoir stimulation can alter the fluid pressure field,potentially inducing the faults to slip in an aseismic or seismic phenomenon.In this work,laboratory friction experiments were performed on split-cutting granite fracture to investigate the effect of fluid pressure on injection-induced slip behavior.The injection experiments spanned a fluid pressure range of 1-20 MPa,which was up to half of the confining pressure.The laboratory results demonstrated that an increase in confining pressure led to a marginal reduction in the friction coefficient,decreasing from a range of 0.70-0.80 at 10 MPa to 0.71-0.75 at 40 MPa.Friction constitutive parameters in experiments with fluid pressure above 10 MPa exhibited a transition from velocity-strengthening to velocity-weakening behavior,while remaining consistently velocity-strengthening below this threshold.Similarly,measurements of dilatancy and critical slip distance exhibited a similar evolution,first increasing and then becoming approximately constant,independent of fluid pressure.The observed microstructural evolution of the split-cutting fractures during slip testing supported these mechanical responses.Post-shear slip,a decrease in the fracture roughness and asperity distribution of the split-cutting fracture was noted,with the decrease in amplitude being more pronounced at high confining pressure.Research may provide a prospect on slip-on faults with fluid pressure.
基金support of the National Natural Science Foundation of China(Grant Nos.51809263)the Open Fund of Key Laboratory of Deep Earth Science and Engineering(Sichuan University)(Grant Nos.DESE201906 and DESE201907)。
文摘Gaomiaozi(GMZ)bentonite is a potential buffer/backfill material for a deep geological disposal of highlevel radioactive waste.It has a wide pore size distribution(PSD)with sizes ranging from several nanometers to more than one hundred microns.Thus,properly characterizing the pore structures of GMZ bentonite is a challenging issue.In this study,pressure-controlled porosimetry(PCP),ratecontrolled porosimetry(RCP),and scanning electron microscopy(SEM)were used to investigate the PSD of GMZ bentonite,The results indicate that each method has its limitation,and a combined use of PCP and RCP is suitable to obtain the full-scale PSD of GMZ bentonite.Moreover,we also compared the full-scale PSD with nuclear magnetic resonance(NMR)result.It is found that there is no significant difference in the range of PSD characterization between NMR and mercury intrusion method(PCP and RCP).However,in a ce rtain range,the detection accuracy of NMR is higher than that of mercury injection method.Finally,permeability prediction based on PCP and SEM data was conducted,and both of the two methods were found to be able to predict the permeability.The combined method is effective to obtain the full-scale PSD of GMZ bentonite,which is the key to estimation of the sealing ability of bentonite buffer.
基金This work was supported by the National Natural Science Foundation of China,NSFC(Nos.U1803118 and 51974296)and the China Scholarship Council(CSC)(award to Fanfei Meng for PhD period at Kyushu University).
文摘Bulking characteristics of gangue are of great significance for the stability of goafs in mining overburden in the caving zones.In this paper,a particle discrete element method with clusters to represent gangue was adopted to explore the bulking coefficient time effect of the broken rock in the caving zone under three-dimensional triaxial compression condition.The phenomena of stress corrosion,deformation,and failure of rock blocks were simulated in the numerical model.Meanwhile,a new criterion of rock fragments damage was put forward.It was found that the broken rock has obvious viscoelastic properties.A new equation based on the Burgers creep model was proposed to predict the bulking coefficient of broken rock.A deformation characteristic parameter of the prediction equation was analyzed,which can be set as a fixed value in the mid-and long-term prediction of the bulking coefficient.There are quadratic function relationships between the deformation characteristic parameter value and Talbot gradation index,axial pressure and confining pressure.
基金the National Natural Science Foundation of China(Nos.52204114,52274145,U22A20165,and 52174089)the Natural Science Foundation of Jiangsu Province(No.BK20210522)+2 种基金the National Key Research and Development Program of China(No.2022YFE0128300)the China Postdoctoral Science Foundation(No.2023M733758)the Shandong Postdoctoral Science Foundation(No.SDCX-ZG-202302037).
文摘The interaction mechanism between coal and rock masses with supporting materials is significant in roadway control, especially in deep underground mining situations where dynamic hazards frequently happened due to high geo-stress and strong disturbed effects. This paper is to investigate the strain energy evolution in the interaction between coal and rock masses with self-designed energy-absorbing props and rock bolts by numerical modeling with the finite difference method. The interaction between rock and rock bolt/prop is accomplished by the cables element and the interface between the inner and outer props. Roadway excavation and coal extraction conditions in deep mining are numerically employed to investigate deformation, plastic zone ranges, strain energy input, accumulation, dissipation,and release. The effect on strain energy input, accumulation, dissipation, and release with rock deformation, and the plastic zone is addressed. A ratio of strain energy accumulation, dissipation, and release with energy input a, β, γ is to assess the dynamic hazards. The effects on roadway excavation and coal extraction steps of a, β, γ are discussed. The results show that:(1) In deep high geo-stress roadways, the energyabsorbing support system plays a dual role in resisting deformation and reducing the scope of plastic zones in surrounding rock, as well as absorbing energy release in the surrounding rock, especially in the coal extraction state to mitigate disturbed effects.(2) The strain energy input, accumulation is dependent on roadway deformation, the strain energy dissipation is relied on plastic zone area and disturbed effects, and strain energy release density is the difference among the three. The function of energyabsorbing rock bolts and props play a key role to mitigate strain energy release density and amount, especially in coal extraction condition, with a peak density value from 4×10^(4) to 1×10^(4)J/m^(3), and amount value from 3.57×10^(8) to 1.90×10^(6)J.(3) When mining is advanced in small steps, the strain energy accumulation is dominated. While in a large step, the released energy is dominant, thus a more dynamic hazards proneness. The energy-absorbing rock bolt and prop can reduce three times strain energy release amount, thus reducing the dynamic hazards. The results suggest that energy-absorbing props and rock bolts can effectively reduce the strain energy in the coal and rock masses, and prevent rock bursts and other hazards.The numerical model developed in this study can also be used to optimize the design of energyabsorbing props and rock bolts for specific mining conditions.
基金support from the National Natural Science Foundation of China(Grant Nos.52174092 and 52104125)the Fundamental Research Funds for the Central Universities,China(Grant No.2022YCPY0202)is gratefully acknowledged.
文摘Through high-precision engraving,self-affine sandstone joint surfaces with various joint roughness coefficients(JRC=3.21e12.16)were replicated and the shear sliding tests under unloading normal stress were conducted regarding various initial normal stresses(1e7 MPa)and numbers of shearing cycles(1 e5).The peak shear stress of fractures decreased with shear cycles due to progressively smooth surface morphologies,while increased with both JRC and initial normal stress and could be verified using the nonlinear Barton-Bandis failure criterion.The joint friction angle of fractures exponentially increased by 62.22%e64.87%with JRC while decreased by 22.1%e24.85%with shearing cycles.After unloading normal stress,the sliding initiation time of fractures increased with both JRC and initial normal stress due to more tortuous fracture morphologies and enhanced shearing resistance capacity.The surface resistance index(SRI)of fractures decreased by 4.35%e32.02%with increasing shearing cycles due to a more significant reduction of sliding initiation shear stress than that for sliding initiation normal stress,but increased by a factor of 0.41e1.64 with JRC.After sliding initiation,the shear displacement of fractures showed an increase in power function.By defining a sliding rate threshold of 5105 m/s,transition from“quasi-static”to“dynamic”sliding of fractures was identified,and the increase of sliding acceleration steepened with JRC while slowed down with shearing cycles.The normal displacement experienced a slight increase before shear sliding due to deformation recovery as the unloading stress was unloaded,and then enhanced shear dilation after sliding initiation due to climbing effects of surface asperities.Dilation was positively related to the shear sliding velocity of fractures.Wear characteristics of the fracture surfaces after shearing failure were evaluated using binary calculation,indicating an increasing shear area ratio by 45.24%e91.02%with normal stress.
基金the National Natural Science Foundation of China(Nos.52374147,42372328,and U23B2091)National Key Research and Development Program of China(No.2023YFC3804200)Xinjiang Uygur Autonomous Region Science and Technology Major Program(No.2023A01002).
文摘Underground pumped storage power plant(UPSP)is an innovative concept for space recycling of abandoned mines.Its realization requires better understanding of the dynamic performance and durability of reservoir rock.This paper conducted ultrasonic detection,split Hopkinson pressure bar(SHPB)impact,mercury intrusion porosimetry(MIP),and backscatter electron observation(BSE)tests to investigate the dynamical behaviour and microstructure of sandstone with cyclical dry-wet damage.A coupling FEM-DEM model was constructed for reappearing mesoscopic structure damage.The results show that dry-wet cycles decrease the dynamic compressive strength(DCS)with a maximum reduction of 39.40%,the elastic limit strength is reduced from 41.75 to 25.62 MPa.The sieved fragments obtain the highest crack growth rate during the 23rd dry-wet cycle with a predictable life of 25 cycles for each rock particle.The pore fractal features of the macropores and micro-meso pores show great differences between the early and late cycles,which verifies the computational statistics analysis of particle deterioration.The numerical results show that the failure patterns are governed by the strain in pre-peak stage and the shear cracks are dominant.The dry-wet cycles reduce the energy transfer efficiency and lead to the discretization of force chain and crack fields.
基金support of the National Natural Science Foundation of China (Grant Nos. 52174133 and 51809263)China Atomic Energy Authority。
文摘The sealing performance of a bentonite barrier is highly dependent on its seepage characteristics, which are directly related to the characteristics of its pore structure. Based on scanning electron microscopy(SEM) and focused ion beam-SEM(FIB-SEM), the pore structure of bentonite was characterized at different scales. First, a reasonable gray threshold was determined through back analysis, and the image was binarized based on the threshold. In addition, binary images were used to analyze bentonite’s pore structure(porosity and pore size distribution). Furthermore, the effects of different algorithms on the pore structure characterization were evaluated. Then, permeability calculations were performed based on the previous pore structure characteristics and a modified permeability prediction model. For permeability prediction based on the three-dimensional model, the effect of pore tortuosity was also considered. Finally, the accuracy of numerical calculations was verified by conducting macroscopic gas and alcohol permeability experiments. This approach provides a better understanding of the microscale mechanism of gas transport in bentonite and the importance of pore structures at different scales in determining its seepage characteristics.
