Analysis of impact of new railway tunnel over-crossing construction on existing railway tunnels
The MIDAS finite element software was used to simulate the construction process of the new railway tunnel passing through the existing tunnel above when the spacing between the two tunnels was 2.76,4.76 and 6.76 m.The displacement and stress changes of the existing tunnel were compared and analyzed,and verified with the on-site monitoring data.Results show that under three different spacings,with the excavation of the new tunnel,the vertical displacement of the existing tunnel rises upward;the horizontal displacement is offset to the left in front of the intersection of the two tunnels,and to the right after the intersection of the two tun-nels;the vertical displacement of the cross-section of the existing tunnel is greater than the horizontal one;the stress change trend of the existing tunnel is bounded by the intersection of the two tunnels,with the fluctuation increasing first and then decreasing,and the maximum tensile stress is located at the left wall of the existing tunnel.The displacement and stress changes of the existing tunnels were inversely proportional to the spacing between the two tunnels:taking the spacing between the two tunnels as the benchmark,for each 2 m increase in the spacing,the maximum vertical displacement of the existing tunnels decreased by 21%and 36%,the maximum horizontal displacement decreased by 57%and 53%,and the maximum tensile stress decreased by 11%and 21%in turn.Based on the displacement results of existing tunnels,the displacement prediction for-mula of key parts of existing tunnels at different spacings was summarized,and the numerical simulation results of existing tunnel displacement and surrounding rock stress at a spacing of 2.76 m were close to the measured data on site.
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