The Experts below are selected from a list of 144 Experts worldwide ranked by ideXlab platform

Jianxun Chen - One of the best experts on this subject based on the ideXlab platform.

  • Performance of Super-Large-Span Tunnel Portal Excavated by Upper Bench CD Method Based on Field Monitoring and Numerical Modeling
    Advances in Civil Engineering, 2020
    Co-Authors: Jianxun Chen, Yao Li, Shaoqiang Zhang, Lijun Chen
    Abstract:

    The number of super-large-span tunnels is increasing in both new construction and reconstruction projects in China recently. In super-large-span tunneling engineering, the deformation properties and mechanical behaviors of tunnel portal structure are more complex than those of common tunnel due to the flatter shape and larger construction span. The mechanical behaviors of rock mass change in response to different sequential excavation methods and supporting parameters. The upper bench CD method has been gradually applied in the construction of super-large-span tunnels in China. In this paper, the design parameters for the supporting structure of super-large-span tunnel were studied by the field monitoring and numerical modeling in a case study of Laohushan tunnel. It was found that the crown settlement was larger than the clearance convergence, and the stress of arch was greater than that of the side wall in tunnel portal section. The invert structure was flat with small curvature. Therefore, the shotcrete was mainly subjected to tensile stress. The use of H200 × 200 Steel Rib with spacing of 60 cm and C25 shotcrete with thickness of 30 cm is recommended. The results of this paper provide basis for the development of design specifications and construction standards for super-large-span tunnels and provide reference for similar projects in the future.

  • Mechanical and Deformation Characteristics and Optimization of Support Parameters for Superlarge-Span Tunnel: A Case Study from Laohushan Tunnel
    Advances in Civil Engineering, 2020
    Co-Authors: Jianxun Chen, Shaoqiang Zhang, Yao Li
    Abstract:

    In the new construction or reconstruction of expressway projects, the number of highway twin tunnels with eight lanes is increasing. However, there are no corresponding design support parameters and measures in the current technical specifications for tunnel design and construction in China. In Laohushan superlarge-span highway tunnel with single hole and four lanes, the deformation behavior and mechanical characteristics of support structures are measured and analyzed. The monitoring results indicated that the deformation of tunnel structure mainly experienced three stages: rapid deformation, slow deformation, and stable deformation, and finally reached a relatively stable state; the structure stress of primary support and secondary lining increases sharply at first and then tends to be stable gradually with the gradual construction of each excavation part in the tunnel; the stress of each measuring point at the Steel Rib is less than the yield limit of Steel Rib (235 MPa), and the support structure is safe and stable in the process of tunnel construction. Then, the structure safety of primary support under different support parameters is simulated and calculated by numerical simulation with Grade IV rock mass, and the reasonable support parameters for Laohushan highway tunnel are studied considering the structural safety and engineering economy. It is suggested to use the H175-type Steel sets with a distance of 80 cm and C25 shotcrete with a thickness of 26 cm. The results could provide reference for similar tunnel projects and provide a basis for the design specification and construction standards for superlarge-span tunnels.

  • Study of Deformation Behaviors and Mechanical Properties of Central Diaphragm in a Large-Span Loess Tunnel by the Upper Bench CD Method
    Advances in Civil Engineering, 2020
    Co-Authors: Jianxun Chen, Yao Li, Yunfei Wu
    Abstract:

    The central diaphragm is often used to reduce the span to maintain the stability and safety of structure in the construction of large-span loess tunnel due to the structure complexities. In this paper, relying on the field monitoring and measurement for Wangcun tunnel in Huangling-Yan’an expressway expansion project, the crown settlement and horizontal convergence of primary support Steel Rib and central diaphragm Steel Rib during the construction are analyzed by the upper bench CD method. According to the internal force transfer, deformation coordination, and arch foot displacement between the two structures, the support system is regarded as the arch-beam fixed structure with three times of statically indeterminate and movable abutment under the loads, and the mechanical calculation model of sidewall Steel Rib and the central diaphragm structure bearing loads and deformation together is established. Finally, through the mechanical model mentioned above, the deformation characteristics of central diaphragm structure and the horizontal convergence in the upper bench of tunnel are calculated and analyzed. The research shows the following: (1) the accumulated settlement of sidewall Steel Rib in Part I is greater than that of the sidewall Steel Rib in Part II, and the accumulated settlement of each part at the support structure during the tunnel excavation is less than the reserved deformation of 150 mm specified in the tunnel excavation; (2) the settlement located at the waist and maximum excavation line position of central diaphragm is mainly affected by the excavation of Parts I and II in upper bench; (3) during the whole excavation process, the excavation of Part I and Part II has the greatest influence on the convergence at arch waist and the maximum excavation line position in Part I, and the convergence at the above two positions all experienced four stages of “convergence-expansion-convergence-gradual stability”; and (4) the errors between the horizontal convergence and the deformation of central diaphragm obtained by the mechanical model and the field monitoring data are between 12.7% and 27.5%. The calculated results are in good agreement with the actual situation. The research can provide a theoretical basis for the study of deformation and mechanical properties for support structure in the construction of large-span loess tunnel by the upper bench CD method.

  • Vertical Load and Settlement at the Foot of Steel Rib with the Support of Feet-Lock Pipe in Soft Ground Tunnel
    Advances in Civil Engineering, 2019
    Co-Authors: Lijun Chen, Jianxun Chen, Yao Li, Taotao Hu
    Abstract:

    In soft ground tunnels, feet-lock pipes have been widely used to decrease the concentration of load and settlement at the foot of Steel Ribs. This paper presents an analytical method to predict the vertical load and settlement at the foot of Steel Ribs with the support of the feet-lock pipe. First, the mechanical model of a Steel Rib and feet-lock pipe combined structure involving the ground reaction at the foot was proposed. In this model, the deformation compatibility among the Steel Rib, the feet-lock pipe, and the ground at the tunnel foot were considered, and an elastic foundation beam model with double parameter for the feet-lock pipe was proposed. Then, based on the proposed mechanical model, the analytical equations for predicting the vertical load and settlement at the foot of the Steel Rib were derived using structural analysis and beam theory on elastic foundation. The predicted vertical loads and settlements were validated by comparing with the results of field measurements and the Winkler foundation beam model for the feet-lock pipe, and the results show that the feet-lock pipe can effectively reduce the load acting on the ground, where the Steel Rib was installed, and finally improve the stability of the tunnel structure.

Yao Li - One of the best experts on this subject based on the ideXlab platform.

  • Performance of Super-Large-Span Tunnel Portal Excavated by Upper Bench CD Method Based on Field Monitoring and Numerical Modeling
    Advances in Civil Engineering, 2020
    Co-Authors: Jianxun Chen, Yao Li, Shaoqiang Zhang, Lijun Chen
    Abstract:

    The number of super-large-span tunnels is increasing in both new construction and reconstruction projects in China recently. In super-large-span tunneling engineering, the deformation properties and mechanical behaviors of tunnel portal structure are more complex than those of common tunnel due to the flatter shape and larger construction span. The mechanical behaviors of rock mass change in response to different sequential excavation methods and supporting parameters. The upper bench CD method has been gradually applied in the construction of super-large-span tunnels in China. In this paper, the design parameters for the supporting structure of super-large-span tunnel were studied by the field monitoring and numerical modeling in a case study of Laohushan tunnel. It was found that the crown settlement was larger than the clearance convergence, and the stress of arch was greater than that of the side wall in tunnel portal section. The invert structure was flat with small curvature. Therefore, the shotcrete was mainly subjected to tensile stress. The use of H200 × 200 Steel Rib with spacing of 60 cm and C25 shotcrete with thickness of 30 cm is recommended. The results of this paper provide basis for the development of design specifications and construction standards for super-large-span tunnels and provide reference for similar projects in the future.

  • Mechanical and Deformation Characteristics and Optimization of Support Parameters for Superlarge-Span Tunnel: A Case Study from Laohushan Tunnel
    Advances in Civil Engineering, 2020
    Co-Authors: Jianxun Chen, Shaoqiang Zhang, Yao Li
    Abstract:

    In the new construction or reconstruction of expressway projects, the number of highway twin tunnels with eight lanes is increasing. However, there are no corresponding design support parameters and measures in the current technical specifications for tunnel design and construction in China. In Laohushan superlarge-span highway tunnel with single hole and four lanes, the deformation behavior and mechanical characteristics of support structures are measured and analyzed. The monitoring results indicated that the deformation of tunnel structure mainly experienced three stages: rapid deformation, slow deformation, and stable deformation, and finally reached a relatively stable state; the structure stress of primary support and secondary lining increases sharply at first and then tends to be stable gradually with the gradual construction of each excavation part in the tunnel; the stress of each measuring point at the Steel Rib is less than the yield limit of Steel Rib (235 MPa), and the support structure is safe and stable in the process of tunnel construction. Then, the structure safety of primary support under different support parameters is simulated and calculated by numerical simulation with Grade IV rock mass, and the reasonable support parameters for Laohushan highway tunnel are studied considering the structural safety and engineering economy. It is suggested to use the H175-type Steel sets with a distance of 80 cm and C25 shotcrete with a thickness of 26 cm. The results could provide reference for similar tunnel projects and provide a basis for the design specification and construction standards for superlarge-span tunnels.

  • Study of Deformation Behaviors and Mechanical Properties of Central Diaphragm in a Large-Span Loess Tunnel by the Upper Bench CD Method
    Advances in Civil Engineering, 2020
    Co-Authors: Jianxun Chen, Yao Li, Yunfei Wu
    Abstract:

    The central diaphragm is often used to reduce the span to maintain the stability and safety of structure in the construction of large-span loess tunnel due to the structure complexities. In this paper, relying on the field monitoring and measurement for Wangcun tunnel in Huangling-Yan’an expressway expansion project, the crown settlement and horizontal convergence of primary support Steel Rib and central diaphragm Steel Rib during the construction are analyzed by the upper bench CD method. According to the internal force transfer, deformation coordination, and arch foot displacement between the two structures, the support system is regarded as the arch-beam fixed structure with three times of statically indeterminate and movable abutment under the loads, and the mechanical calculation model of sidewall Steel Rib and the central diaphragm structure bearing loads and deformation together is established. Finally, through the mechanical model mentioned above, the deformation characteristics of central diaphragm structure and the horizontal convergence in the upper bench of tunnel are calculated and analyzed. The research shows the following: (1) the accumulated settlement of sidewall Steel Rib in Part I is greater than that of the sidewall Steel Rib in Part II, and the accumulated settlement of each part at the support structure during the tunnel excavation is less than the reserved deformation of 150 mm specified in the tunnel excavation; (2) the settlement located at the waist and maximum excavation line position of central diaphragm is mainly affected by the excavation of Parts I and II in upper bench; (3) during the whole excavation process, the excavation of Part I and Part II has the greatest influence on the convergence at arch waist and the maximum excavation line position in Part I, and the convergence at the above two positions all experienced four stages of “convergence-expansion-convergence-gradual stability”; and (4) the errors between the horizontal convergence and the deformation of central diaphragm obtained by the mechanical model and the field monitoring data are between 12.7% and 27.5%. The calculated results are in good agreement with the actual situation. The research can provide a theoretical basis for the study of deformation and mechanical properties for support structure in the construction of large-span loess tunnel by the upper bench CD method.

  • Vertical Load and Settlement at the Foot of Steel Rib with the Support of Feet-Lock Pipe in Soft Ground Tunnel
    Advances in Civil Engineering, 2019
    Co-Authors: Lijun Chen, Jianxun Chen, Yao Li, Taotao Hu
    Abstract:

    In soft ground tunnels, feet-lock pipes have been widely used to decrease the concentration of load and settlement at the foot of Steel Ribs. This paper presents an analytical method to predict the vertical load and settlement at the foot of Steel Ribs with the support of the feet-lock pipe. First, the mechanical model of a Steel Rib and feet-lock pipe combined structure involving the ground reaction at the foot was proposed. In this model, the deformation compatibility among the Steel Rib, the feet-lock pipe, and the ground at the tunnel foot were considered, and an elastic foundation beam model with double parameter for the feet-lock pipe was proposed. Then, based on the proposed mechanical model, the analytical equations for predicting the vertical load and settlement at the foot of the Steel Rib were derived using structural analysis and beam theory on elastic foundation. The predicted vertical loads and settlements were validated by comparing with the results of field measurements and the Winkler foundation beam model for the feet-lock pipe, and the results show that the feet-lock pipe can effectively reduce the load acting on the ground, where the Steel Rib was installed, and finally improve the stability of the tunnel structure.

Qingxiong Wu - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear seismic properties of the Second Saikai Bridge: A concrete filled tubular (CFT) arch bridge
    Engineering Structures, 2005
    Co-Authors: Qingxiong Wu, Mistuhiro Yoshimura, Kazuo Takahashi, Shozo Nakamura, Tadashi Nakamura
    Abstract:

    Abstract The technology of concrete filled tube (CFT) arch bridges has developed rapidly in China since 1990. More than one hundred CFT arch bridges have been built or are now under construction. However, since the weight of a CFT arch Rib is greater than that of a Steel Rib and the arch action is not effective in the out-of-plane direction, the seismic safety of CFT bridges should be evaluated. This paper examines nonlinear seismic responses of the Second Saikai Bridge, which is the first highway bridge in Japan to be a CFT arch bridge. This bridge has a main span length of 240 m. The natural vibration characteristics of this bridge are discussed using a three-dimensional FE model. A nonlinear seismic analysis is performed using the strong ground motions observed in the Hyogo-ken Nanbu Earthquake of Japan. The nonlinear seismic characteristics and seismic safety of this bridge are examined in detail by subjecting the bridge to earthquakes in the out-of-plane direction, longitudinal direction and combined out-of-plane and longitudinal directions. It is found that the analysis should consider the combined out-of-plane and longitudinal excitations.

  • NONLINEAR SEISMIC ANALYSIS OF THE SECOND SAIKAI BRIDGE -CONCRETE FILLED TUBULAR (CFT) ARCH BRIDGE-
    2004
    Co-Authors: H. Fujita, Qingxiong Wu, Mistuhiro Yoshimura, Kazuo Takahashi, Shozo Nakamura, K. Furukawa, Nagasaki Shipyard, Machinery Works
    Abstract:

    The technology of concrete filled Steel tubes (CFT) arch bridges has developed rapidly in China since 1990. More than one hundred CFT arch bridges have been built or are now under construction. However, since the weight of a CFT arch Rib is greater than that of a Steel Rib and the arch action is not effective in the out-of-plane direction, the seismic safety of CFT bridges should be evaluated. This paper examines the free vibrations and nonlinear seismic responses of the Second Saikai Bridge. The first CFT arch bridge to be built in Japan, this bridge has a main span length of 240m. The natural vibration characteristics of this bridge are discussed using a three-dimensional FE model. A nonlinear seismic analysis is performed using the strong ground motions observed in the Hyogo-ken Nanbu Earthquake of Japan. The nonlinear seismic characteristics and seismic safety of this bridge are examined in detail by subjected the bridge to earthquakes in the out-of-plane direction. Seismic safety can be confirmed because the strains in the infilled concrete of the arch Rib do not reach to the yield strains and the curvatures of the piers are within the permitted curvatures.

Tadashi Nakamura - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear seismic properties of the Second Saikai Bridge: A concrete filled tubular (CFT) arch bridge
    Engineering Structures, 2005
    Co-Authors: Qingxiong Wu, Mistuhiro Yoshimura, Kazuo Takahashi, Shozo Nakamura, Tadashi Nakamura
    Abstract:

    Abstract The technology of concrete filled tube (CFT) arch bridges has developed rapidly in China since 1990. More than one hundred CFT arch bridges have been built or are now under construction. However, since the weight of a CFT arch Rib is greater than that of a Steel Rib and the arch action is not effective in the out-of-plane direction, the seismic safety of CFT bridges should be evaluated. This paper examines nonlinear seismic responses of the Second Saikai Bridge, which is the first highway bridge in Japan to be a CFT arch bridge. This bridge has a main span length of 240 m. The natural vibration characteristics of this bridge are discussed using a three-dimensional FE model. A nonlinear seismic analysis is performed using the strong ground motions observed in the Hyogo-ken Nanbu Earthquake of Japan. The nonlinear seismic characteristics and seismic safety of this bridge are examined in detail by subjecting the bridge to earthquakes in the out-of-plane direction, longitudinal direction and combined out-of-plane and longitudinal directions. It is found that the analysis should consider the combined out-of-plane and longitudinal excitations.

Machinery Works - One of the best experts on this subject based on the ideXlab platform.

  • NONLINEAR SEISMIC ANALYSIS OF THE SECOND SAIKAI BRIDGE -CONCRETE FILLED TUBULAR (CFT) ARCH BRIDGE-
    2004
    Co-Authors: H. Fujita, Qingxiong Wu, Mistuhiro Yoshimura, Kazuo Takahashi, Shozo Nakamura, K. Furukawa, Nagasaki Shipyard, Machinery Works
    Abstract:

    The technology of concrete filled Steel tubes (CFT) arch bridges has developed rapidly in China since 1990. More than one hundred CFT arch bridges have been built or are now under construction. However, since the weight of a CFT arch Rib is greater than that of a Steel Rib and the arch action is not effective in the out-of-plane direction, the seismic safety of CFT bridges should be evaluated. This paper examines the free vibrations and nonlinear seismic responses of the Second Saikai Bridge. The first CFT arch bridge to be built in Japan, this bridge has a main span length of 240m. The natural vibration characteristics of this bridge are discussed using a three-dimensional FE model. A nonlinear seismic analysis is performed using the strong ground motions observed in the Hyogo-ken Nanbu Earthquake of Japan. The nonlinear seismic characteristics and seismic safety of this bridge are examined in detail by subjected the bridge to earthquakes in the out-of-plane direction. Seismic safety can be confirmed because the strains in the infilled concrete of the arch Rib do not reach to the yield strains and the curvatures of the piers are within the permitted curvatures.