Purpose-This study aims to research the large cross-section tunnel stability evaluation method corrected after considering the thickness-span ratio.Design/methodology/approach-First,taking the Liuyuan Tunnel of Huangg...Purpose-This study aims to research the large cross-section tunnel stability evaluation method corrected after considering the thickness-span ratio.Design/methodology/approach-First,taking the Liuyuan Tunnel of Huanggang-Huangmei High-Speed Railway as an example and taking deflection of the third principal stress of the surrounding rock at a vault after tunnel excavation as the criterion,the critical buried depth of the large section tunnel was determined.Then,the strength reduction method was employed to calculate the tunnel safety factor under different rock classes and thickness-span ratios,and mathematical statistics was conducted to identify the relationships of the tunnel safety factor with the thickness-span ratio and the basic quality(BQ)index of the rock for different rock classes.Finally,the influences of thickness-span ratio,groundwater,initial stress of rock and structural attitude factors were considered to obtain the corrected BQ,based on which the stability of a large cross-section tunnel with a depth of more than 100 m during mechanized operation was analyzed.This evaluation method was then applied to Liuyuan Tunnel and Cimushan No.2 Tunnel of Chongqing Urban Expressway for verification.Findings-This study shows that under different rock classes,the tunnel safety factor is a strict power function of the thickness-span ratio,while a linear function of the BQ to some extent.It is more suitable to use the corrected BQ as a quantitative index to evaluate tunnel stability according to the actual conditions of the site.Originality/value-The existing industry standards do not consider the influence of buried depth and span in the evaluation of tunnel stability.The stability evaluation method of large section tunnel considering the correction of overburden span ratio proposed in this paper achieves higher accuracy for the stability evaluation of surrounding rock in a full or large-section mechanized excavation of double line high-speed railway tunnels.展开更多
Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration(VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation(LE...Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration(VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation(LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters.展开更多
Deep large span cut holes are difficult to stabilize. The 7801 cut hole in the Lu'an Wuyang Mine was used as this project's background. The main factors affecting large span cut hole stability are analyzed. Pr...Deep large span cut holes are difficult to stabilize. The 7801 cut hole in the Lu'an Wuyang Mine was used as this project's background. The main factors affecting large span cut hole stability are analyzed. Pre- stressed bolting theory was used to design a roof control method for a large span roadway. By reducing the span and applying equal strength coordinated supports the rock could be stabilized. The control prin- ciples and methods are given herein along with the analysis. A double micro arch cross section roadway is defined and its use in solving the current problem is described. Beam arch theory was used to build a model of the double micro arch cross section roadway. A support reverse force model for the arch foot intersection was also derived. A support method based upon reducing the width of the large span in the cut hole is presented. These results show that the reduced span of the roadway roof plus the use of cable anchors and single supports gives an effective way to control the large span cut hole. On site monitoring showed that the reduced span support from the double micro arch cross section roadway design had a significant effect. The roadway surface displacement was small and harmful deformation of the cut hole was effectively controlled. This will ensure its long term stability.展开更多
The binding energy and the photon energy dependence of the photoionization cross-section are calculated for a hydrogenic impurity in GaAs/Ga 1-xAl xAs quantum well wires.The correlation between confined and non-co...The binding energy and the photon energy dependence of the photoionization cross-section are calculated for a hydrogenic impurity in GaAs/Ga 1-xAl xAs quantum well wires.The correlation between confined and non-confined direction of the wire in the variational wave function is taken into account.The results show that the photoionization cross-sections are affected by the width of the wire and that their magnitudes are larger than those in infinite potential quantum well wires.In comparison with previous's results,the variational wave function improves the binding energy and decreases the value of photoionization cross-sections of the hydrogenic impurities,which makes the results more reasonable.展开更多
To study the mechanical responses of large cross-section tunnel reinforced by pretensioned rock bolts and anchor cables, an analytical model is proposed. Considering the interaction between rock mass and bolt-cable su...To study the mechanical responses of large cross-section tunnel reinforced by pretensioned rock bolts and anchor cables, an analytical model is proposed. Considering the interaction between rock mass and bolt-cable support, the strain softening characteristic of rock mass, the elastic-plastic characteristic of bolt-cable support, and the delay effect of installation are considered in the model. To solve the different mechanical cases of tunneling reinforced by bolt-cable support, an analytical approach has been put forward to get the solutions of stress and displacement associated with tunneling. The proposed analytical model is verified by numerical simulation. Moreover, parametric analysis is performed to study the effects of pretension force,cross-section area, length, and supporting density of bolt-cable support on tunnel reinforcement, which can provide references for determining these parameters in tunnel design. Based on the analytical model, a new Ground Response Curve(GRC)considering the reinforcement of bolt-cable support is obtained, which shows the pretension forces and the timely installation are important in bolt-cable support. In addition, the proposed model is applied to the analysis of the Great Wall Station Tunnel, a high-speed railway tunnel with a super large cross-section, which shows that the analytical model of bolt-cable support was a useful tool for preliminary design of large cross-section tunnel.展开更多
Over the past decades, low-energy electron accelerators have been used worldwide for surface curing and sterilization. The beam nonuniformity is an important parameter of the low-energy electron beam with large cross-...Over the past decades, low-energy electron accelerators have been used worldwide for surface curing and sterilization. The beam nonuniformity is an important parameter of the low-energy electron beam with large cross-sections. A simple and accurate measurement system of nonuniformity for the low-energy electron beam with large cross-sections was developed. The main concept consists in the measurement of nonuniformity, which is realized by using a linear actuator to drive two scanning wires through the beam's cross-sections at a fixed speed. The beam distribution can be obtained by sending/collecting the current signals to/from the Data Acquisition (DAQ) software on a laptop by a USB DAQ card. This device is very convenient for the performance testing of a new accelerator at the manufacturer's site. The distribution of the homemade low voltage electron accelerator EBS-300-50 was measured and evaluated.展开更多
基金supported by the NSFC HSR Fundamental Research Joint Fund (Grant No.U1934213)。
文摘Purpose-This study aims to research the large cross-section tunnel stability evaluation method corrected after considering the thickness-span ratio.Design/methodology/approach-First,taking the Liuyuan Tunnel of Huanggang-Huangmei High-Speed Railway as an example and taking deflection of the third principal stress of the surrounding rock at a vault after tunnel excavation as the criterion,the critical buried depth of the large section tunnel was determined.Then,the strength reduction method was employed to calculate the tunnel safety factor under different rock classes and thickness-span ratios,and mathematical statistics was conducted to identify the relationships of the tunnel safety factor with the thickness-span ratio and the basic quality(BQ)index of the rock for different rock classes.Finally,the influences of thickness-span ratio,groundwater,initial stress of rock and structural attitude factors were considered to obtain the corrected BQ,based on which the stability of a large cross-section tunnel with a depth of more than 100 m during mechanized operation was analyzed.This evaluation method was then applied to Liuyuan Tunnel and Cimushan No.2 Tunnel of Chongqing Urban Expressway for verification.Findings-This study shows that under different rock classes,the tunnel safety factor is a strict power function of the thickness-span ratio,while a linear function of the BQ to some extent.It is more suitable to use the corrected BQ as a quantitative index to evaluate tunnel stability according to the actual conditions of the site.Originality/value-The existing industry standards do not consider the influence of buried depth and span in the evaluation of tunnel stability.The stability evaluation method of large section tunnel considering the correction of overburden span ratio proposed in this paper achieves higher accuracy for the stability evaluation of surrounding rock in a full or large-section mechanized excavation of double line high-speed railway tunnels.
基金supported by the National Natural Science Foundation of China (Nos. 51179179 and 51079136)
文摘Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration(VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation(LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters.
基金Financial supports are from the National Natural Science Foundation of China (No. 50874104)the Scientific Research Industrialization Project of Jiangsu Universities (No. JH07-023)
文摘Deep large span cut holes are difficult to stabilize. The 7801 cut hole in the Lu'an Wuyang Mine was used as this project's background. The main factors affecting large span cut hole stability are analyzed. Pre- stressed bolting theory was used to design a roof control method for a large span roadway. By reducing the span and applying equal strength coordinated supports the rock could be stabilized. The control prin- ciples and methods are given herein along with the analysis. A double micro arch cross section roadway is defined and its use in solving the current problem is described. Beam arch theory was used to build a model of the double micro arch cross section roadway. A support reverse force model for the arch foot intersection was also derived. A support method based upon reducing the width of the large span in the cut hole is presented. These results show that the reduced span of the roadway roof plus the use of cable anchors and single supports gives an effective way to control the large span cut hole. On site monitoring showed that the reduced span support from the double micro arch cross section roadway design had a significant effect. The roadway surface displacement was small and harmful deformation of the cut hole was effectively controlled. This will ensure its long term stability.
文摘The binding energy and the photon energy dependence of the photoionization cross-section are calculated for a hydrogenic impurity in GaAs/Ga 1-xAl xAs quantum well wires.The correlation between confined and non-confined direction of the wire in the variational wave function is taken into account.The results show that the photoionization cross-sections are affected by the width of the wire and that their magnitudes are larger than those in infinite potential quantum well wires.In comparison with previous's results,the variational wave function improves the binding energy and decreases the value of photoionization cross-sections of the hydrogenic impurities,which makes the results more reasonable.
基金supported by the National Key Research and Development Program of China (Grant No. 2017YFC0805401)the National Natural Science Foundation of China (Grant No. 51738002)+1 种基金the China Railway Corporation Research and Development Program of Science and Technology (Grant No. 2014004-C)the Fundamental Research Funds for the Central Universities (Grant No. C17JB00030)。
文摘To study the mechanical responses of large cross-section tunnel reinforced by pretensioned rock bolts and anchor cables, an analytical model is proposed. Considering the interaction between rock mass and bolt-cable support, the strain softening characteristic of rock mass, the elastic-plastic characteristic of bolt-cable support, and the delay effect of installation are considered in the model. To solve the different mechanical cases of tunneling reinforced by bolt-cable support, an analytical approach has been put forward to get the solutions of stress and displacement associated with tunneling. The proposed analytical model is verified by numerical simulation. Moreover, parametric analysis is performed to study the effects of pretension force,cross-section area, length, and supporting density of bolt-cable support on tunnel reinforcement, which can provide references for determining these parameters in tunnel design. Based on the analytical model, a new Ground Response Curve(GRC)considering the reinforcement of bolt-cable support is obtained, which shows the pretension forces and the timely installation are important in bolt-cable support. In addition, the proposed model is applied to the analysis of the Great Wall Station Tunnel, a high-speed railway tunnel with a super large cross-section, which shows that the analytical model of bolt-cable support was a useful tool for preliminary design of large cross-section tunnel.
文摘Over the past decades, low-energy electron accelerators have been used worldwide for surface curing and sterilization. The beam nonuniformity is an important parameter of the low-energy electron beam with large cross-sections. A simple and accurate measurement system of nonuniformity for the low-energy electron beam with large cross-sections was developed. The main concept consists in the measurement of nonuniformity, which is realized by using a linear actuator to drive two scanning wires through the beam's cross-sections at a fixed speed. The beam distribution can be obtained by sending/collecting the current signals to/from the Data Acquisition (DAQ) software on a laptop by a USB DAQ card. This device is very convenient for the performance testing of a new accelerator at the manufacturer's site. The distribution of the homemade low voltage electron accelerator EBS-300-50 was measured and evaluated.
