Abstract
Based on the Zaosheng No. 3 tunnel of the Yinchuan-Xi’an high-speed railway, the surrounding rock pressure, contact pressure of the primary support, and secondary lining and internal force of the secondary lining concrete are systematically tested using a vibrating wire sensor, and the correlation between the advance construction distance and the surrounding rock release rate is studied with finite element software. The results show that the pressure on the surrounding rock is low when the deeply buried soil tunnel is excavated and can be divided into three stages: rapid growth, slow growth, and flattening with time. It is more reasonable to calculate the surrounding rock pressure by using tunnel planning calculations. For the contact pressure, although the value of each measuring point in the inverted arch changes a little, the arch pressure obviously has the characteristics of rapid growth and a sharp rebound. Most of the test points of the second lining concrete show a compression state, which is far less than the ultimate compressive strength. At the same time, the initial support of the tunnel bears a large load, while the secondary lining bears a relatively small force, and the load sharing ratio of the two ranges between 0.1 and 0.7; with the progress of the excavation section, the surrounding rock deformation (deformation release rate) increases gradually. When the excavation face is close to the monitoring section, the deformation (deformation release rate) is the most severe. With the increase in the distance between the excavation section and the monitoring section, the deformation (deformation release rate) tends to be flat.
Highlights
Based on the Zaosheng No 3 tunnel of the Yinchuan-Xi’an high-speed railway, the surrounding rock pressure, contact pressure of the primary support, and secondary lining and internal force of the secondary lining concrete are systematically tested using a vibrating wire sensor, and the correlation between the advance construction distance and the surrounding rock release rate is studied with finite element software. e results show that the pressure on the surrounding rock is low when the deeply buried soil tunnel is excavated and can be divided into three stages: rapid growth, slow growth, and flattening with time
Introduction e space-time effect of tunnel refers to the active mobilization of two types of self-bearing constraints on the surrounding rock, namely, the “semicircular dome” constraint in the axial direction and the “circular” constraint in the cross-sectional direction during tunnel excavation [1]. ese constraints are supported by dynamic adjustments to achieve a steady state in the tunnel. e step method is often used by designers of large-section railway tunnels because of its flexibility, applicability, and high stability of the excavation surface, while utilizing the tunnel space-time effect
Field Test e tunnel is greatly affected by the cross-section form, excavation method, and other factors. e “three benches and seven steps” excavation method divides the tunnel section into seven small sections and excavates them in different procedures. erefore, the construction steps are divided into nine phases: excavation of upper stage ⟶ left of middle step ⟶ right of middle step ⟶ left of lower step ⟶ right of lower step ⟶ excavation of inverted arch ⟶ construction of secondary lining inverted arch ⟶ construction of circumferential second lining ⟶ monitoring end. ese steps are used to explore the influence law of each process on the tunnel surrounding rock pressure. e nine steps are marked, as shown in Figures 5 and 6
Summary
Received 10 March 2021; Revised 12 April 2021; Accepted 24 April 2021; Published 7 May 2021. The initial support of the tunnel bears a large load, while the secondary lining bears a relatively small force, and the load sharing ratio of the two ranges between 0.1 and 0.7; with the progress of the excavation section, the surrounding rock deformation (deformation release rate) increases gradually. E step method is often used by designers of large-section railway tunnels because of its flexibility, applicability, and high stability of the excavation surface, while utilizing the tunnel space-time effect. In addition to the design of the tunnel itself, the type of surrounding rock, the characteristics of the lining, and the type of load, the constructional state is the leading cause of the stress distribution in the surrounding rock and the mechanical characteristics of the supporting structure based on the experience in long-term engineering practice. Tunnel Excavation Parameters. e tunnel was excavated with the “three benches and seven steps to reserve core soil” method. is method divides the palm surface into seven excavation surfaces, and the steps are staggered and advanced in parallel along the tunnel longitudinally. is method has a small exposed area for a single excavation and a relatively stable working surface. e process can be
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