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.
Highlights
Along with the implementation of China’s “ e Belt and the Road” strategic plan and the rapid development of national economy and traffic construction in the western region, the number of motor vehicles has been increasing and the traffic volume has been increasingly saturated in recent years
In terms of mechanical calculation model, the mechanical model for central diaphragm structure is too simplified and rough, the deformation coordination between the sidewall steel rib and the central diaphragm steel rib as well as the displacement at the arch foot of steel rib is not considered, and the stress of structural joint and the central diaphragm is not clear, which cannot truly reflect the bearing mode and mechanism of support structure in the construction process. erefore, for the large-span loess tunnel constructed by upper bench central diaphragm method (CD) method, the mechanical and deformation characteristics of central diaphragm structure need to be further studied, and the safety and stability of structure directly affect the construction safety and cause a series of engineering problems
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. rough 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 compared with the field monitoring data. e good agreement between the two results proves that the mechanical model and the calculation method have strong applicability and high reliability for the tunnel project. e study can provide theoretical basis for the analysis of mechanical and deformation characteristics for support structure during the construction of large-span loess tunnel by the upper bench CD method
Summary
Along with the implementation of China’s “ e Belt and the Road” strategic plan and the rapid development of national economy and traffic construction in the western region, the number of motor vehicles has been increasing and the traffic volume has been increasingly saturated in recent years. The previous studies on the mechanical properties of central diaphragm mainly focused on the project construction by CD, CRD, and two-side pilot hole method, while the researches on the central diaphragm structure for large-span loess tunnel constructed by the upper bench CD method have not been studied. Erefore, for the large-span loess tunnel constructed by upper bench CD method, the mechanical and deformation characteristics of central diaphragm structure need to be further studied, and the safety and stability of structure directly affect the construction safety and cause a series of engineering problems. Based on the field monitoring of Wangcun tunnel project in Huangyan expressway, this paper analyzes and discusses the crown settlement and horizontal convergence of steel rib at sidewall and the central diaphragm structure during the construction by upper bench CD method and establishes the mechanical calculation model with the sidewall steel rib and the central diaphragm structure bearing loads and deformation together. 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. rough 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 compared with the field monitoring data. e good agreement between the two results proves that the mechanical model and the calculation method have strong applicability and high reliability for the tunnel project. e study can provide theoretical basis for the analysis of mechanical and deformation characteristics for support structure during the construction of large-span loess tunnel by the upper bench CD method
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