The successful completion of the Zhengzhou-Xi＇an high-speed railway project has greatly improved the construction level of China＇s large-section loess tunnels, and has resulted in significant progress being made in ...The successful completion of the Zhengzhou-Xi＇an high-speed railway project has greatly improved the construction level of China＇s large-section loess tunnels, and has resulted in significant progress being made in both design theory and construction technology. This paper systematically summarizes the tech- nical characteristics and main problems of the large-section loess tunnels on China＇s high-speed railway, including classification of the surrounding rock, design of the supporting structure, surface settlement and cracking control, and safe and rapid construction methods. On this basis, the key construction tech- niques of loess tunnels with large sections for high-speed railway are expounded from the aspects of design and construction. The research results show that the classification of loess strata surrounding large tunnels should be based on the geological age of the loess, and be determined by combining the plastic index and the water content. In addition, the influence of the buried depth should be considered. During tunnel excavation disturbance, if the tensile stress exceeds the soil tensile or shear strength, the surface part of the sliding trend plane can be damaged, and visible cracks can form. The pressure of the surrounding rock of a large-section loess tunnel should be calculated according to the buried depth, using the corresponding formula. A three-bench seven-step excavation method of construction was used as the core technology system to ensure the safe and rapid construction of a large-section loess tunnel, following a field test to optimize the construction parameters and determine the engineering measures to stabilize the tunnel face. The conclusions and methods presented here are of great significance in revealing the strata and supporting mechanics of large-section loess tunnels, and in optimizing the supporting structure design and the technical parameters for construction.展开更多
It has been a focus of debate for a large time on construction methods for large-span loess tunnel.Reasonable construction method has much effect on stability of tunnel and construction schedule.Deformation and failur...It has been a focus of debate for a large time on construction methods for large-span loess tunnel.Reasonable construction method has much effect on stability of tunnel and construction schedule.Deformation and failure of surrounding rock are quite complex.Associating with the large-span loess tunnel of Zhengzhou- Xi'an high-speed passenger rail line in China,large scale model test with geometric proportion 1:20 is applied to study on dynamic mechanical behavior of various construction methods.They include full-face excavation with support and no support,and benching method with support.It is found that pre-deformation and stress accumulation take place ahead of working face.The effects of three construction methods are further studied,particularly in terms of tunnel displacement and stress changes.It is revealed that benching method transfers load to an unexcavated area,limits horizontal deformation,reduces stress concentration effectively,lengthens the distance between location of peak for stress concentration and working face,and consequently increases stability.The model test results not only supply theoretical foundation for determination of reasonable construction method,but also can act as reference for similar tunnel and underground engineering construction.展开更多
Loess tunnels are widely used in transportation engineering and are irreplaceable parts of transportation infrastructure. In this paper, a dynamic finite element method is used to analyze the coupled effects of a trai...Loess tunnels are widely used in transportation engineering and are irreplaceable parts of transportation infrastructure. In this paper, a dynamic finite element method is used to analyze the coupled effects of a train vibration load and rainfall seepage. By calculating the variation in the safety factor of a loess tunnel because of the effects of various factors, such as different rainfall intensities and soil thicknesses, the dynamic stability of the loess tunnel is studied under the condition of a near-field pulse-like earthquake. The results show that the security and stability of the tunnel decrease gradually with decreasing burial depth. In addition, the plastic strain of the tunnel is mainly distributed on both sides of the vault and the feet, and the maximum value of the critical strain occurs on both sides of the arch feet. Because of the effects of the train vibration load and rainfall seepage, the safety factor of the loess tunnel structure decreases to a certain degree. Moreover, the range and maximum value of the plastic strain increase to various degrees.展开更多
文摘The successful completion of the Zhengzhou-Xi＇an high-speed railway project has greatly improved the construction level of China＇s large-section loess tunnels, and has resulted in significant progress being made in both design theory and construction technology. This paper systematically summarizes the tech- nical characteristics and main problems of the large-section loess tunnels on China＇s high-speed railway, including classification of the surrounding rock, design of the supporting structure, surface settlement and cracking control, and safe and rapid construction methods. On this basis, the key construction tech- niques of loess tunnels with large sections for high-speed railway are expounded from the aspects of design and construction. The research results show that the classification of loess strata surrounding large tunnels should be based on the geological age of the loess, and be determined by combining the plastic index and the water content. In addition, the influence of the buried depth should be considered. During tunnel excavation disturbance, if the tensile stress exceeds the soil tensile or shear strength, the surface part of the sliding trend plane can be damaged, and visible cracks can form. The pressure of the surrounding rock of a large-section loess tunnel should be calculated according to the buried depth, using the corresponding formula. A three-bench seven-step excavation method of construction was used as the core technology system to ensure the safe and rapid construction of a large-section loess tunnel, following a field test to optimize the construction parameters and determine the engineering measures to stabilize the tunnel face. The conclusions and methods presented here are of great significance in revealing the strata and supporting mechanics of large-section loess tunnels, and in optimizing the supporting structure design and the technical parameters for construction.
基金the National Natural Science Foundation of China(Nos. 50978172 and 51078318)the New Century Excellent Talents in University(No. 10-0667)
文摘It has been a focus of debate for a large time on construction methods for large-span loess tunnel.Reasonable construction method has much effect on stability of tunnel and construction schedule.Deformation and failure of surrounding rock are quite complex.Associating with the large-span loess tunnel of Zhengzhou- Xi'an high-speed passenger rail line in China,large scale model test with geometric proportion 1:20 is applied to study on dynamic mechanical behavior of various construction methods.They include full-face excavation with support and no support,and benching method with support.It is found that pre-deformation and stress accumulation take place ahead of working face.The effects of three construction methods are further studied,particularly in terms of tunnel displacement and stress changes.It is revealed that benching method transfers load to an unexcavated area,limits horizontal deformation,reduces stress concentration effectively,lengthens the distance between location of peak for stress concentration and working face,and consequently increases stability.The model test results not only supply theoretical foundation for determination of reasonable construction method,but also can act as reference for similar tunnel and underground engineering construction.
基金supported in part by the National Natural Science Foundation of China(Grant No.51478212)the Education Ministry Doctoral Tutor Foundation of China(Grant No.20136201110003)
文摘Loess tunnels are widely used in transportation engineering and are irreplaceable parts of transportation infrastructure. In this paper, a dynamic finite element method is used to analyze the coupled effects of a train vibration load and rainfall seepage. By calculating the variation in the safety factor of a loess tunnel because of the effects of various factors, such as different rainfall intensities and soil thicknesses, the dynamic stability of the loess tunnel is studied under the condition of a near-field pulse-like earthquake. The results show that the security and stability of the tunnel decrease gradually with decreasing burial depth. In addition, the plastic strain of the tunnel is mainly distributed on both sides of the vault and the feet, and the maximum value of the critical strain occurs on both sides of the arch feet. Because of the effects of the train vibration load and rainfall seepage, the safety factor of the loess tunnel structure decreases to a certain degree. Moreover, the range and maximum value of the plastic strain increase to various degrees.
基金Projects(52208392,52068044)supported by the National Natural Science Foundation of ChinaProject(2021M693843)supported by the China Postdoctoral Science Foundation+1 种基金Project(21RJ7RA309)supported by Natural Science Foundation of Gansu Province,ChinaProject(1520260306)supported by Tianyou Youth Talent Lift Program of Lanzhou Jiaotong University,China。
