Shearing behavior and failure mechanism of bolt-grout interface are of great significance for load transfer capacity and design of rock bolting system.In this paper,direct shear tests on bolt-grout interfaces under co...Shearing behavior and failure mechanism of bolt-grout interface are of great significance for load transfer capacity and design of rock bolting system.In this paper,direct shear tests on bolt-grout interfaces under constant normal load(CNL) conditions were conducted to investigate the effects of bolt profile(i.e.rib spacing and rib height) and grout mixture on the bolt-grout interface in terms of mechanical behaviors and failure modes.Test results showed that the peak shear strength and the deformation capacity of the bolt-grout interface are highly dependent on the bolt profile and grout mixture,suggesting that bolt performances can be optimized,which were unfortunately ignored in the previous studies.A new interface failure mode,i.e.'sheared-crush' mode,was proposed,which was characterized by progressive crush failure of the grout asperities between steel ribs during shearing.It was shown that the interface failure mode mainly depends on the normal stress level and rib spacing,compared with the rib height and grout mixture for the range of tested parameters in this study.展开更多
Numerical analysis of the total energy release of surrounding rocks excavated by drill-and-blast (D&B) method and tunnel boring machine (TBM) method is presented in the paper. The stability of deep tunnels during...Numerical analysis of the total energy release of surrounding rocks excavated by drill-and-blast (D&B) method and tunnel boring machine (TBM) method is presented in the paper. The stability of deep tunnels during excavation in terms of energy release is also discussed. The simulation results reveal that energy release during blasting excavation is a dynamic process. An intense dynamic effect is captured at large excavation footage. The magnitude of energy release during full-face excavation with D&B method is higher than that with TBM method under the same conditions. The energy release rate (ERR) and speed (ERS) also have similar trends. Therefore, the rockbursts in tunnels excavated by D&B method are frequently encountered and more intensive than those by TBM method. Since the space after tunnel face is occupied by the backup system of TBM, prevention and control of rockbursts are more difficult. Thus, rockbursts in tunnels excavated by TBM method with the same intensity are more harmful than those in tunnels by D&B method. Reducing tunneling rate of TBM seems to be a good means to decrease ERR and risk of rockburst. The rockbursts observed during excavation of headrace tunnels at Jinping II hydropower station in West China confirm the analytical results obtained in this paper.展开更多
Rock sampling with traditional coring method would cause initial damage to rock samples induced by in-situ stress relief during coring.To solve this problem,a damage-free coring method is proposed in this paper.The pr...Rock sampling with traditional coring method would cause initial damage to rock samples induced by in-situ stress relief during coring.To solve this problem,a damage-free coring method is proposed in this paper.The proposed coring scheme is numerically modeled first,and then it is verified by comparative laboratory tests using rock samples both obtained by conventional coring method and the proposed damage-free coring method.The result indicates that the in-situ stresses in sampling area could be reduced by 30%-50% through drilling a certain number of destressing holes around the whole sampling area.The spacing between adjacent destressing holes is about 10 cm.The average uniaxial compressive strength(UCS) of rock samples obtained by the damage-free coring method in Jinping II hydropower station with overburden depth of 1 900 m is higher than that of samples obtained by the conventional coring method with the same depth by 5%-15% and an average of 8%.In addition,the effectiveness of damage-free coring method can also be verified by acoustic emission(AE) monitoring.The AE events monitored during uniaxial compression test of damage-free coring samples is fewer than that of conventional coring samples at the primarily loading phase.展开更多
To the Editor:Injuries are an important yet neglected cause of health burden,and the millions of injuryrelated deaths that occur each year reflect large disparities in terms of gender,race,and socioeconomic status.^([...To the Editor:Injuries are an important yet neglected cause of health burden,and the millions of injuryrelated deaths that occur each year reflect large disparities in terms of gender,race,and socioeconomic status.^([1])With the progress of urbanization and the number of motor vehicles increasing,pedestrians,cyclists,and drivers are brought into close contact,increasing the risk for all.^([2])In 2019,one of the leading causes of injuryrelated disability-adjusted life-years(DALYs)for all ages was road injuries(ranked seventh).^([1])Understanding the burden of transport injuries and how they are distributed among different regions and countries worldwide is essential for policy-making.^([3])展开更多
Application of membrane filtration in sugar production is attractive because it can reduce the usage of chemicals,produce high-quality clarified juice,and obtain various high value-added products.However,some technica...Application of membrane filtration in sugar production is attractive because it can reduce the usage of chemicals,produce high-quality clarified juice,and obtain various high value-added products.However,some technical problems,such as insufficient membrane performance,high sucrose loss in membrane retentate,severe membrane fouling,and incomplete cleaning protocols,limit its industrial applications.In order to facilitate the development of membrane technology for sugar production,this review summarizes recent progress on the applications of membrane filtration in different stages of sugar production as well as the integrated membrane processes for various purposes.Moreover,some important issues including membrane fouling,membrane cleaning,economic feasibility and engineering problems of the membrane-based sugar production process are discussed.Finally,the existing challenges and future research prospects for the industrialization of this green technique are pointed out.展开更多
To the Editor:Combined nuclei stimulation may have a synergistic effect on controlling the symptoms of nervous system diseases and improving quality of life.[1]However,increasing of leads may increase costs and compli...To the Editor:Combined nuclei stimulation may have a synergistic effect on controlling the symptoms of nervous system diseases and improving quality of life.[1]However,increasing of leads may increase costs and complications.[2]Therefore,our study aims to investigate the safety and feasibility of the single curved lead,which can simultaneously reach both subthalamic nucleus(STN)and pedunculopontine nucleus(PPN).展开更多
基金supported by the Key Projects of the Yalong River Joint Fund of the National Natural Science Foundation of China(Grant No.U1865203)the National Natural Science Foundation of China(Grant No.51279201)+1 种基金Special project of the National Natural Science Foundation of China(Grant No.41941018)The partial support from the Youth Innovation Promotion Association,Chinese Academy of Sciences。
文摘Shearing behavior and failure mechanism of bolt-grout interface are of great significance for load transfer capacity and design of rock bolting system.In this paper,direct shear tests on bolt-grout interfaces under constant normal load(CNL) conditions were conducted to investigate the effects of bolt profile(i.e.rib spacing and rib height) and grout mixture on the bolt-grout interface in terms of mechanical behaviors and failure modes.Test results showed that the peak shear strength and the deformation capacity of the bolt-grout interface are highly dependent on the bolt profile and grout mixture,suggesting that bolt performances can be optimized,which were unfortunately ignored in the previous studies.A new interface failure mode,i.e.'sheared-crush' mode,was proposed,which was characterized by progressive crush failure of the grout asperities between steel ribs during shearing.It was shown that the interface failure mode mainly depends on the normal stress level and rib spacing,compared with the rib height and grout mixture for the range of tested parameters in this study.
基金Supported by the National Key Basic Research and Development Program of China (2010CB732003)the National Natural Science Foundation of China (51009013,50909077)
文摘Numerical analysis of the total energy release of surrounding rocks excavated by drill-and-blast (D&B) method and tunnel boring machine (TBM) method is presented in the paper. The stability of deep tunnels during excavation in terms of energy release is also discussed. The simulation results reveal that energy release during blasting excavation is a dynamic process. An intense dynamic effect is captured at large excavation footage. The magnitude of energy release during full-face excavation with D&B method is higher than that with TBM method under the same conditions. The energy release rate (ERR) and speed (ERS) also have similar trends. Therefore, the rockbursts in tunnels excavated by D&B method are frequently encountered and more intensive than those by TBM method. Since the space after tunnel face is occupied by the backup system of TBM, prevention and control of rockbursts are more difficult. Thus, rockbursts in tunnels excavated by TBM method with the same intensity are more harmful than those in tunnels by D&B method. Reducing tunneling rate of TBM seems to be a good means to decrease ERR and risk of rockburst. The rockbursts observed during excavation of headrace tunnels at Jinping II hydropower station in West China confirm the analytical results obtained in this paper.
基金Supported by the National Basic Research Program of China (973 Program) (2010CB732003)the National Natural Science Foundation of China (51009013,50909077)
文摘Rock sampling with traditional coring method would cause initial damage to rock samples induced by in-situ stress relief during coring.To solve this problem,a damage-free coring method is proposed in this paper.The proposed coring scheme is numerically modeled first,and then it is verified by comparative laboratory tests using rock samples both obtained by conventional coring method and the proposed damage-free coring method.The result indicates that the in-situ stresses in sampling area could be reduced by 30%-50% through drilling a certain number of destressing holes around the whole sampling area.The spacing between adjacent destressing holes is about 10 cm.The average uniaxial compressive strength(UCS) of rock samples obtained by the damage-free coring method in Jinping II hydropower station with overburden depth of 1 900 m is higher than that of samples obtained by the conventional coring method with the same depth by 5%-15% and an average of 8%.In addition,the effectiveness of damage-free coring method can also be verified by acoustic emission(AE) monitoring.The AE events monitored during uniaxial compression test of damage-free coring samples is fewer than that of conventional coring samples at the primarily loading phase.
基金supported by grants from the Program for Excellent Talents in the First Affiliated Hospital of Fujian Medical University(Nos.YJCRC-B-KDZ2021 and YYXQN-DCY2021).
文摘To the Editor:Injuries are an important yet neglected cause of health burden,and the millions of injuryrelated deaths that occur each year reflect large disparities in terms of gender,race,and socioeconomic status.^([1])With the progress of urbanization and the number of motor vehicles increasing,pedestrians,cyclists,and drivers are brought into close contact,increasing the risk for all.^([2])In 2019,one of the leading causes of injuryrelated disability-adjusted life-years(DALYs)for all ages was road injuries(ranked seventh).^([1])Understanding the burden of transport injuries and how they are distributed among different regions and countries worldwide is essential for policy-making.^([3])
基金the Science and Technology Service Network Program of Chinese Academy of Sciences(KFJ-STSQYZX-096)the Province Key Research and Development Program of Shandong(2019JZZY010348)Youth Innovation Promotion Association(2017069)of Chinese Academy of Sciences.
文摘Application of membrane filtration in sugar production is attractive because it can reduce the usage of chemicals,produce high-quality clarified juice,and obtain various high value-added products.However,some technical problems,such as insufficient membrane performance,high sucrose loss in membrane retentate,severe membrane fouling,and incomplete cleaning protocols,limit its industrial applications.In order to facilitate the development of membrane technology for sugar production,this review summarizes recent progress on the applications of membrane filtration in different stages of sugar production as well as the integrated membrane processes for various purposes.Moreover,some important issues including membrane fouling,membrane cleaning,economic feasibility and engineering problems of the membrane-based sugar production process are discussed.Finally,the existing challenges and future research prospects for the industrialization of this green technique are pointed out.
基金National Natural Science Foundation of China(No. 81901395)
文摘To the Editor:Combined nuclei stimulation may have a synergistic effect on controlling the symptoms of nervous system diseases and improving quality of life.[1]However,increasing of leads may increase costs and complications.[2]Therefore,our study aims to investigate the safety and feasibility of the single curved lead,which can simultaneously reach both subthalamic nucleus(STN)and pedunculopontine nucleus(PPN).