Dynamic Responses of Soils around a One-Hole Double-Track Tunnel with the Metro Train Meeting

The single-hole double-track shield tunnel with a large diameter has been one of the optimized schemes for those Metro meeting tunnels crossing long water areas. Compared with single-hole single-track tunnels, train-meeting scenarios occur in single-hole double-track tunnels, which results in a greater dynamic loading and a longer action time. By far, the thorough understanding of the dynamic response and liquefiability of the soils around the single-hole double-track tunnels, when crossing liquefiable soil layers, is still lacked. In this paper, a typical profile of Nanjing Metro Line 10, of the crossing-river section near Jiangxinzhou Station, is taken as an example. Based on the multibody dynamics, we established the train-rail coupling model to obtain the train dynamic load. Subsequently, in view of the single running scenario and four typical meeting scenarios, the train-tunnel-soil FEM model is developed to analyse the dynamical responses of the soils around the tunnel. The results indicate the vertical acceleration of the tunnel substrata exhibits an exponential attenuation trend with an increase of the distance; the horizontal acceleration of the ground surface exhibits an enlarged area within 10–25 m from the tunnel centerline. Also, the displacement of the soil layer under the tunnel increases cyclically in the period of the Metro train passing and rebounds slowly after the train passes. When the wheels of two Metro trains act simultaneously, the peak compression strain increases superimposedly; when the act is out of sync, the peak compression strain occurs concentrated and significant increase does not occur. Moreover, the larger the vibration amplitude the Metro train causes, the greater the excess pore water pressure occurs. Beyond a certain depth range, the influence of the vibration vanishes. The ratio of the maximal pore water pressure to the total stress is less than 1, suggesting that liquefaction does not occur in the silty-fine sand soil layer beneath the tunnel. The research results can be used to estimate the longitudinal differential settlement under long-term operation conditions and be helpful in regulating running speed of the Metro trains and planning the maintenance measures for the track flatness of the tunnel.

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