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<p>Major seismic events have demonstrated that underground structures, such as tunnels, can significantly alter the propagation and behavior of seismic waves as they pass through the ground. As twin tunnels are increasingly being constructed for transportation purposes, understanding their effects on ground response under seismic loading has become critical. However, current knowledge regarding the effects of twin tunnels limited to some numerical studies and no comprehensive studies have been previously performed using experimental field measurements techniques to investigate the effect of these tunnels along different excavation phases. To address this knowledge gap, the under-construction twin tunnels of Shiraz (southwest of Iran) subway provided us an opportunity to compare surface seismic response during different stage of construction. The experimental measurements include 90 single-station ambient noise recordings at two different sites, under three distinct conditions: before tunnel construction, after the excavation of a single tunnel, and following the completion of the adjacent twin tunnels. The recorded ambient noise data were analyzed using horizontal-to-vertical spectral ratios (HVSR) to identify changes in resonance frequencies and amplification patterns. Subsequently, the selected sites were modeled numerically using the finite element method, assuming linear elastic behavior and simulating vertically propagating SV and P waves. In the frequency domain, various components of the transfer function, amplification patterns, and spectral ratios were computed. Both experimental (HVSR Ratio) and numerically calculated transfer function before tunnel excavation show a clear amplification in frequencies below 1&#xa0;Hz. However, after tunnel excavation, this low frequency peak on HVSR curves disappeared for the measurements performed just above the tunnels. Outside this zone, the observed low frequency peak remains unchanged and similar to the state before tunnel excavation (free-field condition). In numerical simulations deamplification is observed for higher frequencies at the tunnel-affected zone, however any change cannot be observed in low frequencies domain due to the negligible dimension of tunnels relative to large wavelengths of incident waves.</p>

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Experimental Assessment of Ground Seismic Response Before and After Twin Tunnels Excavation and Comparison with Numerical Modeling

  • 期刊论文

  • 发表日期：

    2025年10月27日

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  • Fateme Ahmadi,
  • Ebrahim Haghshenas,
  • Mohsen Kamalian,
  • Saeed Soltani

摘要

Major seismic events have demonstrated that underground structures, such as tunnels, can significantly alter the propagation and behavior of seismic waves as they pass through the ground. As twin tunnels are increasingly being constructed for transportation purposes, understanding their effects on ground response under seismic loading has become critical. However, current knowledge regarding the effects of twin tunnels limited to some numerical studies and no comprehensive studies have been previously performed using experimental field measurements techniques to investigate the effect of these tunnels along different excavation phases. To address this knowledge gap, the under-construction twin tunnels of Shiraz (southwest of Iran) subway provided us an opportunity to compare surface seismic response during different stage of construction. The experimental measurements include 90 single-station ambient noise recordings at two different sites, under three distinct conditions: before tunnel construction, after the excavation of a single tunnel, and following the completion of the adjacent twin tunnels. The recorded ambient noise data were analyzed using horizontal-to-vertical spectral ratios (HVSR) to identify changes in resonance frequencies and amplification patterns. Subsequently, the selected sites were modeled numerically using the finite element method, assuming linear elastic behavior and simulating vertically propagating SV and P waves. In the frequency domain, various components of the transfer function, amplification patterns, and spectral ratios were computed. Both experimental (HVSR Ratio) and numerically calculated transfer function before tunnel excavation show a clear amplification in frequencies below 1 Hz. However, after tunnel excavation, this low frequency peak on HVSR curves disappeared for the measurements performed just above the tunnels. Outside this zone, the observed low frequency peak remains unchanged and similar to the state before tunnel excavation (free-field condition). In numerical simulations deamplification is observed for higher frequencies at the tunnel-affected zone, however any change cannot be observed in low frequencies domain due to the negligible dimension of tunnels relative to large wavelengths of incident waves.