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Large-scale transfer nodes renovation of the existing metro hub stations involves many issues such as space stress conversion, demolition and construction scheme, and existing station protection. Relying on the comprehensive transportation hub transformation project of the Huangmugang station of Shenzhen metro, the construction difficulties and corresponding countermeasures faced in large-scale transfer nodes renovation of the existing metro stations are summarized using engineering analogy, simulation calculation, and construction verification, obtaining a complete set of key construction techniques. The research results reveal the following: (1) To ensure the normal operation and structural safety of the existing stations, a renovation principle, supporting first, then dismantling, sectional construction, and columns before beams, is established to gradually achieve force conversion. (2) A temporary support system with anti-overturning measures is arranged, and an automatic servo system is used to automatically compensate for the gap between the temporary steel column and the structural plate, successfully achieving the structural stress system conversion from temporary column to permanent column, and ensuring controllable deformation. (3) A novel multifunctional enclosure composed of steel skeleton, sound-absorbing cotton, and fire-resistant and sound-absorbing boards effectively minimize the impact of renovation construction on station operation. (4) Manual hand-held air picks are recommended to use to break down the enclosure structure, and manual breaking, diamond rope saw cutting, and high-pressure water jet crushing methods can be used for main structure according to specific requirements. (5) During construction, key measures such as anti-floating, waterproofing, and monitoring should be employed to strictly control structural deformation, uneven settlement, and differential settlement. [ABSTRACT FROM AUTHOR]

To ensure the safety and stability of the bridge during construction, construction monitoring of the bridge and its temporary support system is required. The bridge closure stage involves system conversion, and the effect of unbalanced load on the bridge during cantilever construction needs to be considered. The construction monitoring of the temporary support system of the thin-walled pier bridge based on the reconstruction of Gaozeng bridge was studied. The MIDAS model of the thin-walled pier bridge was established to simulate the cantilever construction process of the continuous beam. The safety of the thin-walled pier construction process was analyzed by combining theory and simulation. The results show that even under the most dangerous working conditions, the stresses on the thin-walled piers are within the safe range. The construction monitoring of the temporary support system ensures the safety of the whole process of bridge construction. [ABSTRACT FROM AUTHOR]

In this study, the static response of the preliminary pilot tunnels excavation to the ground, and the dynamic response of the group cavern system under seismic excitation under the use of the construction of a metro station based on the Pile-Beam-Arch approach are investigated through numerical calculation. The results suggest that the excavation sequences of "top first and then bottom" and "middle first and then both sides" can generate the minimum ground settlement. When the pilot tunnels were excavated, the horizontal PGA (peak ground acceleration) amplification coefficient tends to increase with significant nonlinear characteristics under the excitation of EI Centro wave with a horizontal acceleration of 0.15 g, and the horizontal PGA amplification coefficient reaches the maximum at the ground surface. The effect of horizontal acceleration around the upper pilot tunnels increases. Under the static load, the maximum principal stress of the lining structure after the completion of the pilot tunnels is largely concentrated at the foot of the arch of the pilot tunnel, and the maximum principal stress value is 1.124 MPa. The maximum principal stress is primarily concentrated at the foot of the arch and the foot of the upper and lower guide tunnel under seismic excitation, and the maximum principal stress value is 1.424 MPa. This study reveals that a reasonable excavation sequence can be employed when the pilot tunnels are being excavated to control the settlement. Furthermore, the support of the arch and footing of the pilot tunnels should be enhanced during the seismic design. [ABSTRACT FROM AUTHOR]

In this study, the static response of the preliminary pilot tunnels excavation to the ground, and the dynamic response of the group cavern system under seismic excitation under the use of the construction of a metro station based on the Pile-Beam-Arch approach are investigated through numerical calculation. The results suggest that the excavation sequences of “top first and then bottom” and “middle first and then both sides” can generate the minimum ground settlement. When the pilot tunnels were excavated, the horizontal PGA (peak ground acceleration) amplification coefficient tends to increase with significant nonlinear characteristics under the excitation of EI Centro wave with a horizontal acceleration of 0.15 g, and the horizontal PGA amplification coefficient reaches the maximum at the ground surface. The effect of horizontal acceleration around the upper pilot tunnels increases. Under the static load, the maximum principal stress of the lining structure after the completion of the pilot tunnels is largely concentrated at the foot of the arch of the pilot tunnel, and the maximum principal stress value is 1.124 MPa. The maximum principal stress is primarily concentrated at the foot of the arch and the foot of the upper and lower guide tunnel under seismic excitation, and the maximum principal stress value is 1.424 MPa. This study reveals that a reasonable excavation sequence can be employed when the pilot tunnels are being excavated to control the settlement. Furthermore, the support of the arch and footing of the pilot tunnels should be enhanced during the seismic design.

The long-term behavior of rock mass plays a vital role in the overall stability of underground structures. One possible long-term scenario is the degradation of the rock mass, especially in unstable clay-bearing rocks susceptible to water ingress. Lack of efficient countermeasures in extreme cases could significantly affect the physical and mechanical properties of rocks and alter the engineering behavior to some extent. In this research, we describe the case of the Golab access tunnel where it is subject to failure in a specific section containing meta-shales. The situation was considered to have occurred as a consequence of long-term deteriorating phenomenon after a 5-year period. To characterize the rock mass, point load tests were conducted on the rock samples in failure zones and values were compared with the ones obtained through primary geotechnical studies. Slake durability index (SDI) was also used to assess the vulnerability of rocks to changes in moisture content and was correlated to point load values. Additionally, GSI was measured in the failed regions, and the decreasing trend was presented in accordance with time. By taking advantage of the engineering characteristics, ground reaction curves in short-term and long-term conditions were obtained. It was deduced that the temporary support system applied to the tunnel in this section cannot provide a safe margin against long-term strains imposed by the ground. Therefore, another support system was suggested and applied to the unstable sections of tunnel to prevent further hazards. [ABSTRACT FROM AUTHOR]