Numerical analysis and application of the construction method for the small interval tunnel in the turn line of metro

Abstract

The surrounding rock may become unstable or even fall down and the initial support may crack and be destroyed when the construction method of the underground excavation tunnel is not properly selected in the turn line of metro. . A section of the Santunbei turn line of Urumqi Metro Line 1# was taken as the engineering background. The proposed construction method was analyzed by numerical simulation. Numerical analysis shows that the final surface settlement caused by the proposed construction method is 3.0 mm and the horizontal convergence is 3.2 mm. It also turns out that the proposed construction method causes less deformation, and the method can be applied to the construction of the small interval tunnel in the Santunbei turn line of metro. The rationality of the method and numerical model was further verified by comparison between the monitored data of surface settlement, horizontal convergence and vault sinking, and numerical simulation results. Finally, the deformation and stress of the six construction methods were compared. The deformation and stress caused by the six construction methods are almost the same. It indicates that the construction spacing between the left and right tunnels does not affect the safety of tunnel construction. Therefore, the appropriate construction spacing could be selected according to the resource configuration, instead of deformation and stress.

Optimization of Construction Parameters and Deformation Characteristics of Large‐Section Loess Tunnel: A Case Study from Xi’an Metro

“…e supporting structure of vault is mainly concentrated in tensile stress, and the maximum tensile stress is 4.44∼4.76 MPa. erefore, during the construction process, it is necessary to strengthen the deformation monitoring of connection between steel supporting and initial supporting [33,34,36,38], thus improving the load strength of supporting structure and resistance ability of deformation of surrounding rock. Figure 14(e) shows the relationship between the maximum principal stress of the supporting structure of the CK9 + 462 section and the excavation face distance (L 3 ).…”

“…Based on the Code for Monitoring Measurement of Urban Rail Transit Engineering (GB50911-2013) [33] and the actual situation on the site, the monitoring level of the research section of this tunnel is determined to be Class II. Setting up the monitoring sections at 100 m intervals in the direction perpendicular to the tunnel axis, there are 11 monitoring points for each monitoring section.…”

“…e settlement of tunnel vault is an important indicator for monitoring the longitudinal deformation, controlling the stable state of surrounding rock, and ensuring the safe construction of the tunnel, especially in shallow-buried loess tunnel [33,38]. In order to directly reflect the vault deformation by testing the time-history curve of vault settlement, monitoring points 1, 2, and 3 are, respectively, set on the tunnel vault to monitor the vault settlement characteristics.…”

“…Cording [29] monitored the surface settlement data of a double-hole tunnel subway in Washington and found that the asymmetric settlement trough on the surface after the completion of subsequent tunnel excavation was related to the excavation effect of the previous tunnel. According to the above analysis, because the urban subway tunnel is subjected to complex underground traffic network and buildings [30][31][32][33], the tunnel excavation process only depends on construction experience and later monitoring data to ensure the construction safety and tunnel stability have certain blindness. erefore, it is of great significance to effectively control the excavation spacing of different caverns to guide the safe construction of large-section and neighborhood tunnels.…”

A Theoretical Calculation Method of the Unsupported Span for the Shallow Tunnel in the Soft Stratum

“…Apart from the surrounding rock classification, tunnel depth, excavation method, and construction method, the unsupported span is also an essential factor affecting the three issues above. For a specific project, surrounding rock classification, tunnel depth, excavation method, and construction method are determined, so the unsupported span is particularly important [12][13][14]. Especially in construction of tunnels in shallow buried soft stratum, oversizing the unsupported span and reduced stability of soft stratum may cause tunnel face instability and excessive ground surface settlement, which may further cause the arch crown collapse.…”