This study is to determine the support mechanism of pre-stressed expandable props for the stope roof in room- and-pillar mining, which is crucial for maintaining stability and preventing roof collapse in mines. Utiliz...This study is to determine the support mechanism of pre-stressed expandable props for the stope roof in room- and-pillar mining, which is crucial for maintaining stability and preventing roof collapse in mines. Utilizing an engineering case from a gold mine in Dandong, China, a laboratory-based similar test is conducted to extract the actual roof characteristic curve. This test continues until the mining stope collapses due to a U-shaped failure. Concurrently, a semi-theoretical method for obtaining the roof characteristic curve is proposed and verified against the actual curve. The semi-theoretical method calculated that the support force and vertical displacement at the demarcation point between the elastic and plastic zones of the roof characteristic curve are 5.0 MPa and 8.20 mm, respectively, corroborating well with the laboratory-based similar test results of 0.22 MPa and 0.730 mm. The weakening factor for the plastic zone in the roof characteristic curve was semi-theoretically estimated to be 0.75. The intersection between the actual roof characteristic curve and the support characteristic curves of expandable props, natural pillars, and concrete props indicates that the expandable prop is the most effective “yielding support” for the stope roof in room-and-pillar mining. That is, the deformation and failure of the stope roof can be effectively controlled with proper release of roof stress. This study provides practical insights for optimizing support strategies in room-and-pillar mining, enhancing the safety and efficiency of mining operations.展开更多
This paper aims to determine the load bearing capacity of pre-stressed expandable props with different geometries and load eccentricities for flexible support in underground mining or excavation.It is deduced that the...This paper aims to determine the load bearing capacity of pre-stressed expandable props with different geometries and load eccentricities for flexible support in underground mining or excavation.It is deduced that the expandable device could have much higher strength(>89 MPa)by laboratory tests,and the load bearing capacity of the expandable prop may depend on the stability of the supporting steel pipe structure.A good agreement was found between the laboratory test and numerical results in terms of the load bearing capacity and the final macro-bending failure pattern for expandable props with heights of 1.5 and 2.7 m,and the theoretical calculation for the strength of traditional steel structures is not directly suitable for the expandable props.Moreover,additional numerical simulations were performed for the expandable props with different normalized slenderness ratiosλ_(n)and loading eccentric distances e.The variation of stability coefficient of the expandable prop is in line with the Perry-Robertson equation and its correlation coefficients are fitted as a of 0.979 and b of 0.314.For estimating the load bearing capacity of the expandable props,the strength equation for traditional steel structures is improved by introducing a bending magnification factor and by modifying the normalized slenderness ratio to a converted slenderness ratio.Based on the underground field monitoring for the strength of expandable props with different heights,the empirical eccentric distances were back calculated,and a safety factor is introduced to obtain the designed strength of the expandable prop.In addition,a four-step design procedure is proposed for the expandable prop.展开更多
Are you tred of regular selfies?Try a self-photo studio!The lights and camera are ready for you.At the studio,you can fix your hair.There are clothes and props.You can use those and take fun photos.Bring your friends ...Are you tred of regular selfies?Try a self-photo studio!The lights and camera are ready for you.At the studio,you can fix your hair.There are clothes and props.You can use those and take fun photos.Bring your friends with you.Then you can take photos together.Pose in silly ways and have fun!You can take the photos home and remember your good time.展开更多
Shale gas is an important component of unconventional oil and gas resources.Studying the imbibition behavior is helpful to optimize flowback parameters and enhance gas recovery.Recent imbibition studies have focused o...Shale gas is an important component of unconventional oil and gas resources.Studying the imbibition behavior is helpful to optimize flowback parameters and enhance gas recovery.Recent imbibition studies have focused on shale matrix,and the pressure conditions discussed were mostly atmospheric.The initial imbibition behavior begins from propped fractures to matrix,but there are few studies working on explaining the imbibition behavior in propped fractures or the phenomenon of many shale wells exhibit higher productivity after a“soaking”period.Therefore,propped fracture samples were designed for imbibition and migration experiments.In order to accurately study the mechanism and main influencing factors of fracturing fluid imbibition and migration in propped and unpropped shale fractures under high temperature and high pressure,a series of experiments based on nuclear magnetic resonance(NMR)were carried out.Results showed that NMR T_(2) spectra of all samples exhibited a bimodal distribution.The final imbibition volume of fracturing fluid was positively related to pressure and fracture width.The imbibition effect of fracturing fluid was more evident in matrix pores under high pressure.In the migration during soaking stage,the fracturing fluid gradually migrated from large pores to small pores and gradually displaced the shale gas from the matrix,thus allowing the water blocking in propped fractures to self-unlock to some extent.Gas permeability decreased in the imbibition stage,while it recovered in the migration stage to some extent.展开更多
The Self-Propping Phase-transition Fracturing Technology(SPFT)represents a novel and environmentally friendly approach for a cost-effective and efficient development of the world’s abundant unconventional resources,e...The Self-Propping Phase-transition Fracturing Technology(SPFT)represents a novel and environmentally friendly approach for a cost-effective and efficient development of the world’s abundant unconventional resources,especially in the context of a carbon-constrained sustainable future.SPFT involves the coupling of Thermal,Hydraulic,Mechanical,and Chemical(THMC)fields,which makes it challenging to understand the mechanism and path of hydraulic fracture propagation.This study addresses these challenges by developing a set of THMC multifield coupling models based on SPFT parameters and the physical/chemical characteristics of the Phase-transition Fracturing Fluid System(PFFS).An algorithm,integrating the Finite Element Method,Discretized Virtual Internal Bonds,and Element Partition Method(FEM-DVIB-EPM),is proposed and validated through a case study.The results demonstrate that the FEM-DVIB-EPM coupling algorithm reduces complexity and enhances solving efficiency.The length of the hydraulic fracture increases with the quantity and displacement of PFFS,and excessive displacement may result in uncontrolled fracture height.Within the parameters considered,a minimal difference in fracture length is observed when the PFFS amount exceeds 130 m^(3),that means the fracture length tends to stabilize.This study contributes to understanding the hydraulic fracture propagation mechanism induced by SPFT,offering insights for optimizing hydraulic fracturing technology and treatment parameters.展开更多
This paper will discuss the question about how to sustain and promote learners＇ motivation in TEFL. A framework is proposed, which provides some suggestions to English teacher about how they could do better and what ...This paper will discuss the question about how to sustain and promote learners＇ motivation in TEFL. A framework is proposed, which provides some suggestions to English teacher about how they could do better and what they should pay more attention to. This paper is indicated in the following five parts.展开更多
With the continuous improvement of the educational environment, the teaching resources of primary school Chinese are becoming more and more abundant. In the hybrid teaching of online and offline combination, various i...With the continuous improvement of the educational environment, the teaching resources of primary school Chinese are becoming more and more abundant. In the hybrid teaching of online and offline combination, various information-based teaching equipment and software, as well as offline teaching equipment and teaching resources, make the teaching resources of Chinese course sufficient and diverse. In this context, how to make good use of the teaching resources around to teach Chinese well has become an important problem faced by primary school Chinese teachers. Based on this, this study has a positive significance. Using the teaching resources around to teach Chinese well can be carried out from two aspects: The use of information teaching resources and the use of physical equipment resources. This paper discusses the specific application strategies in detail.展开更多
Rock bursts signify extreme behavior in coal mine strata and severely threaten the safety of the lives of miners, as well as the effectiveness and productivity of miners. In our study, an elastic-plastic-brittle model...Rock bursts signify extreme behavior in coal mine strata and severely threaten the safety of the lives of miners, as well as the effectiveness and productivity of miners. In our study, an elastic-plastic-brittle model for the deformation and failure of coal/rock was established through theoretical analyses, laboratory experiments and field testing, simulation and other means, which perfectly predict sudden and delayed rock bursts. Based on electromagnetic emission (EME), acoustic emission (AE) and microseism (MS) effects in the process from deformation until impact rupture of coal-rock combination samples, a multi-parameter identification of premonitory technology was formed, largely depending on these three forms of emission. Thus a system of classification for forecasting rock bursts in space and time was established. We have presented the intensity weakening theory for rock bursts and a strong-soft-strong (3S) structural model for controlling the impact on rock surrounding roadways, with the objective of laying a theoretical foundation and establishing references for parameters for the weakening control of rock bursts. For the purpose of prevention, key technical parameters of directional hydraulic fracturing are revealed. Based on these results, as well as those from deep-hole controlled blasting in coal seams and rock, integrated control techniques were established and anti-impact hydraulic props, suitable for roadways subject to hazards from rockbursts have also been developed. These technologies have been widely used in most coal mines in China, subject to these hazards and have achieved remarkable economic and social benefits.展开更多
The effect of rare earth on the microstructures, mechanical properties and inclu sions in low sulphur Nb-Ti-bearing steel were investigated. It is shown that t h e transverse yield point, the traverse tensile strength...The effect of rare earth on the microstructures, mechanical properties and inclu sions in low sulphur Nb-Ti-bearing steel were investigated. It is shown that t h e transverse yield point, the traverse tensile strength and elongation of testin g steels decrease initially and then rise with increasing content of rare earth. The impact energy values of the testing steels exhibit a contrary trend. Proper amount of rare earth in the steels can improve the anisotropy of impact toughne ss above -20 ℃ and it does not affect the type of microstructures which ar e st ill composed of ferrites and pearlites, but the pearlite amount increases. On one hand, rare earth cleans the molten steel and reduces the amount of inclusions; on the other hand, rare earth makes the inclusions spheroidizd, refi ned and dispersed, and thus improves the distribution of inclusions.展开更多
In order to optimize gob-side entry in fully-mechanized working face in moderate-thick-coal seams, we adopt a new attempt to pack roadside by pumping ordinary concrete, which is very important for the development of g...In order to optimize gob-side entry in fully-mechanized working face in moderate-thick-coal seams, we adopt a new attempt to pack roadside by pumping ordinary concrete, which is very important for the development of gob-side entry technology. The concrete has a long initial setting time and a low initial strength. So it is difficult to control the surrounding rock. In this paper, we analyze the effect of using roadside cable to reinforce supporting in gob-side entry surrounding rock controlling based on elas-tic-plastic and material mechanics knowledge. And then we propose a scheme that cable is used to reinforce roadside supporting and a single hydraulic prop is used as the temporary supporting in gob side. Using the numerical simulation software FLAC2D, we numerically simulated supporting scheme. Results of both the 2D modeling and the industrial test on No.3117 face in Jingang Mine prove that the scheme is feasible. The results show that the technology of protecting the roadway in gob-entry retained efficiently make up the deficiency of roadside packing with ordinary concrete, effectively control the roof strata and acquire a good result of retaining roadway.展开更多
The Mg-4.58Gd-0.45Y-0.01 Er alloys with different volume fractions of columnar crystals in hard orientation(orientation factor ofbasal plane slip system is less than 0.2)were prepared by changing the pulling rate to r...The Mg-4.58Gd-0.45Y-0.01 Er alloys with different volume fractions of columnar crystals in hard orientation(orientation factor ofbasal plane slip system is less than 0.2)were prepared by changing the pulling rate to regulate the crystal growth orientation.Tensile tests were performed on the Mg-4.58Gd-0.45Y-0.01 Er alloy at room temperature,and the structure after deformation was investigated by electron backscatter diffraction(EBSD).Subsequently,the strengthening mechanism of columnar crystals in hard orientation was explored.The results show if orientation factors ofbasal plane slip system of columnar crystals are all greater than 0.4(soft orientation),the alloy has low yield strength σ_(s)(64 MPa),but great work hardening ability,and ultimate tensile strength σ_(b) and elongationδare 114 MPa and 37.3%,respectively.If orientation factors ofbasal plane slip system of columnar crystals are all less than 0.2(hard orientation),the alloy has high strength(σ_(s),125 MPa),but poor plasticity(δ,6.32%).If the"hard orientation"and the"soft orientation"columnar crystals are arranged alternately along the direction perpendicular to the crystal growth,the alloy has both superior strength(σ_(s),102 MPa)and excellent plasticity(δ,22.5%)at room temperature.The improved comprehensive mechanical property can be attributed to two factors.On the one hand,the"hard orientation"columnar crystals can prevent the"soft orientation"crystals deforming,so the strength is improved.On the other hand,the"hard orientation"columnar crystals themselves can withstand a certain amount of deformation to retain appropriate plasticity.展开更多
基金Project(2022YFC2903801) supported by the National Key Research and Development Program of ChinaProjects(52374117, 52274115) supported by the National Natural Science Foundation of China。
文摘This study is to determine the support mechanism of pre-stressed expandable props for the stope roof in room- and-pillar mining, which is crucial for maintaining stability and preventing roof collapse in mines. Utilizing an engineering case from a gold mine in Dandong, China, a laboratory-based similar test is conducted to extract the actual roof characteristic curve. This test continues until the mining stope collapses due to a U-shaped failure. Concurrently, a semi-theoretical method for obtaining the roof characteristic curve is proposed and verified against the actual curve. The semi-theoretical method calculated that the support force and vertical displacement at the demarcation point between the elastic and plastic zones of the roof characteristic curve are 5.0 MPa and 8.20 mm, respectively, corroborating well with the laboratory-based similar test results of 0.22 MPa and 0.730 mm. The weakening factor for the plastic zone in the roof characteristic curve was semi-theoretically estimated to be 0.75. The intersection between the actual roof characteristic curve and the support characteristic curves of expandable props, natural pillars, and concrete props indicates that the expandable prop is the most effective “yielding support” for the stope roof in room-and-pillar mining. That is, the deformation and failure of the stope roof can be effectively controlled with proper release of roof stress. This study provides practical insights for optimizing support strategies in room-and-pillar mining, enhancing the safety and efficiency of mining operations.
基金This work was financially supported by the National Key Research and Development Program of China(No.2022YFC2903804)the National Natural Science Foundation of China(Nos.52004054,52274115,51874068 and 52074062).
文摘This paper aims to determine the load bearing capacity of pre-stressed expandable props with different geometries and load eccentricities for flexible support in underground mining or excavation.It is deduced that the expandable device could have much higher strength(>89 MPa)by laboratory tests,and the load bearing capacity of the expandable prop may depend on the stability of the supporting steel pipe structure.A good agreement was found between the laboratory test and numerical results in terms of the load bearing capacity and the final macro-bending failure pattern for expandable props with heights of 1.5 and 2.7 m,and the theoretical calculation for the strength of traditional steel structures is not directly suitable for the expandable props.Moreover,additional numerical simulations were performed for the expandable props with different normalized slenderness ratiosλ_(n)and loading eccentric distances e.The variation of stability coefficient of the expandable prop is in line with the Perry-Robertson equation and its correlation coefficients are fitted as a of 0.979 and b of 0.314.For estimating the load bearing capacity of the expandable props,the strength equation for traditional steel structures is improved by introducing a bending magnification factor and by modifying the normalized slenderness ratio to a converted slenderness ratio.Based on the underground field monitoring for the strength of expandable props with different heights,the empirical eccentric distances were back calculated,and a safety factor is introduced to obtain the designed strength of the expandable prop.In addition,a four-step design procedure is proposed for the expandable prop.
文摘Are you tred of regular selfies?Try a self-photo studio!The lights and camera are ready for you.At the studio,you can fix your hair.There are clothes and props.You can use those and take fun photos.Bring your friends with you.Then you can take photos together.Pose in silly ways and have fun!You can take the photos home and remember your good time.
基金The authors gratefully acknowledge the support of the National Natural Science Foundation of China(Grant Nos.52174036,51774243,51904257,51874251)the Sichuan Province Science and Technology Program(Grant Nos.2021YJ0345,2022JDJQ0009,2022NSFSC0186).
文摘Shale gas is an important component of unconventional oil and gas resources.Studying the imbibition behavior is helpful to optimize flowback parameters and enhance gas recovery.Recent imbibition studies have focused on shale matrix,and the pressure conditions discussed were mostly atmospheric.The initial imbibition behavior begins from propped fractures to matrix,but there are few studies working on explaining the imbibition behavior in propped fractures or the phenomenon of many shale wells exhibit higher productivity after a“soaking”period.Therefore,propped fracture samples were designed for imbibition and migration experiments.In order to accurately study the mechanism and main influencing factors of fracturing fluid imbibition and migration in propped and unpropped shale fractures under high temperature and high pressure,a series of experiments based on nuclear magnetic resonance(NMR)were carried out.Results showed that NMR T_(2) spectra of all samples exhibited a bimodal distribution.The final imbibition volume of fracturing fluid was positively related to pressure and fracture width.The imbibition effect of fracturing fluid was more evident in matrix pores under high pressure.In the migration during soaking stage,the fracturing fluid gradually migrated from large pores to small pores and gradually displaced the shale gas from the matrix,thus allowing the water blocking in propped fractures to self-unlock to some extent.Gas permeability decreased in the imbibition stage,while it recovered in the migration stage to some extent.
基金supported by the National Natural Science Foundation of China(52179112)the Open Fund of National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Southwest Petroleum University)(PLN2023-02)Fundamental Research Funds for the Central Universities(2021FZZX001-14).
文摘The Self-Propping Phase-transition Fracturing Technology(SPFT)represents a novel and environmentally friendly approach for a cost-effective and efficient development of the world’s abundant unconventional resources,especially in the context of a carbon-constrained sustainable future.SPFT involves the coupling of Thermal,Hydraulic,Mechanical,and Chemical(THMC)fields,which makes it challenging to understand the mechanism and path of hydraulic fracture propagation.This study addresses these challenges by developing a set of THMC multifield coupling models based on SPFT parameters and the physical/chemical characteristics of the Phase-transition Fracturing Fluid System(PFFS).An algorithm,integrating the Finite Element Method,Discretized Virtual Internal Bonds,and Element Partition Method(FEM-DVIB-EPM),is proposed and validated through a case study.The results demonstrate that the FEM-DVIB-EPM coupling algorithm reduces complexity and enhances solving efficiency.The length of the hydraulic fracture increases with the quantity and displacement of PFFS,and excessive displacement may result in uncontrolled fracture height.Within the parameters considered,a minimal difference in fracture length is observed when the PFFS amount exceeds 130 m^(3),that means the fracture length tends to stabilize.This study contributes to understanding the hydraulic fracture propagation mechanism induced by SPFT,offering insights for optimizing hydraulic fracturing technology and treatment parameters.
文摘This paper will discuss the question about how to sustain and promote learners＇ motivation in TEFL. A framework is proposed, which provides some suggestions to English teacher about how they could do better and what they should pay more attention to. This paper is indicated in the following five parts.
文摘With the continuous improvement of the educational environment, the teaching resources of primary school Chinese are becoming more and more abundant. In the hybrid teaching of online and offline combination, various information-based teaching equipment and software, as well as offline teaching equipment and teaching resources, make the teaching resources of Chinese course sufficient and diverse. In this context, how to make good use of the teaching resources around to teach Chinese well has become an important problem faced by primary school Chinese teachers. Based on this, this study has a positive significance. Using the teaching resources around to teach Chinese well can be carried out from two aspects: The use of information teaching resources and the use of physical equipment resources. This paper discusses the specific application strategies in detail.
基金Project 2010CB226805 supported by the National Natural Science Foundation of Chinaprovided by the National Basic Research Program of China (2010CB226805)+1 种基金the National Eleventh Five-Year Key Science & Technology Project (2006BAK04B02, 2006BAK04B06)the National Natural Science Foundation of China (50474068), are gratefully acknowledged
文摘Rock bursts signify extreme behavior in coal mine strata and severely threaten the safety of the lives of miners, as well as the effectiveness and productivity of miners. In our study, an elastic-plastic-brittle model for the deformation and failure of coal/rock was established through theoretical analyses, laboratory experiments and field testing, simulation and other means, which perfectly predict sudden and delayed rock bursts. Based on electromagnetic emission (EME), acoustic emission (AE) and microseism (MS) effects in the process from deformation until impact rupture of coal-rock combination samples, a multi-parameter identification of premonitory technology was formed, largely depending on these three forms of emission. Thus a system of classification for forecasting rock bursts in space and time was established. We have presented the intensity weakening theory for rock bursts and a strong-soft-strong (3S) structural model for controlling the impact on rock surrounding roadways, with the objective of laying a theoretical foundation and establishing references for parameters for the weakening control of rock bursts. For the purpose of prevention, key technical parameters of directional hydraulic fracturing are revealed. Based on these results, as well as those from deep-hole controlled blasting in coal seams and rock, integrated control techniques were established and anti-impact hydraulic props, suitable for roadways subject to hazards from rockbursts have also been developed. These technologies have been widely used in most coal mines in China, subject to these hazards and have achieved remarkable economic and social benefits.
文摘The effect of rare earth on the microstructures, mechanical properties and inclu sions in low sulphur Nb-Ti-bearing steel were investigated. It is shown that t h e transverse yield point, the traverse tensile strength and elongation of testin g steels decrease initially and then rise with increasing content of rare earth. The impact energy values of the testing steels exhibit a contrary trend. Proper amount of rare earth in the steels can improve the anisotropy of impact toughne ss above -20 ℃ and it does not affect the type of microstructures which ar e st ill composed of ferrites and pearlites, but the pearlite amount increases. On one hand, rare earth cleans the molten steel and reduces the amount of inclusions; on the other hand, rare earth makes the inclusions spheroidizd, refi ned and dispersed, and thus improves the distribution of inclusions.
基金support from the National Nature Science Foundation of China (No50874124)
文摘In order to optimize gob-side entry in fully-mechanized working face in moderate-thick-coal seams, we adopt a new attempt to pack roadside by pumping ordinary concrete, which is very important for the development of gob-side entry technology. The concrete has a long initial setting time and a low initial strength. So it is difficult to control the surrounding rock. In this paper, we analyze the effect of using roadside cable to reinforce supporting in gob-side entry surrounding rock controlling based on elas-tic-plastic and material mechanics knowledge. And then we propose a scheme that cable is used to reinforce roadside supporting and a single hydraulic prop is used as the temporary supporting in gob side. Using the numerical simulation software FLAC2D, we numerically simulated supporting scheme. Results of both the 2D modeling and the industrial test on No.3117 face in Jingang Mine prove that the scheme is feasible. The results show that the technology of protecting the roadway in gob-entry retained efficiently make up the deficiency of roadside packing with ordinary concrete, effectively control the roof strata and acquire a good result of retaining roadway.
基金the National Natural Science Foundation of China(Nos.51775099 and 51675092)the Natural Science Foundation of Hebei Province(E2018501032 and E2018501033)。
文摘The Mg-4.58Gd-0.45Y-0.01 Er alloys with different volume fractions of columnar crystals in hard orientation(orientation factor ofbasal plane slip system is less than 0.2)were prepared by changing the pulling rate to regulate the crystal growth orientation.Tensile tests were performed on the Mg-4.58Gd-0.45Y-0.01 Er alloy at room temperature,and the structure after deformation was investigated by electron backscatter diffraction(EBSD).Subsequently,the strengthening mechanism of columnar crystals in hard orientation was explored.The results show if orientation factors ofbasal plane slip system of columnar crystals are all greater than 0.4(soft orientation),the alloy has low yield strength σ_(s)(64 MPa),but great work hardening ability,and ultimate tensile strength σ_(b) and elongationδare 114 MPa and 37.3%,respectively.If orientation factors ofbasal plane slip system of columnar crystals are all less than 0.2(hard orientation),the alloy has high strength(σ_(s),125 MPa),but poor plasticity(δ,6.32%).If the"hard orientation"and the"soft orientation"columnar crystals are arranged alternately along the direction perpendicular to the crystal growth,the alloy has both superior strength(σ_(s),102 MPa)and excellent plasticity(δ,22.5%)at room temperature.The improved comprehensive mechanical property can be attributed to two factors.On the one hand,the"hard orientation"columnar crystals can prevent the"soft orientation"crystals deforming,so the strength is improved.On the other hand,the"hard orientation"columnar crystals themselves can withstand a certain amount of deformation to retain appropriate plasticity.
