震態主頻對山岳隧道變形關聯性分析:現地監測與數值模擬比較

Abstract

隧道作為基礎建設的一環，扮演著連接交通網絡、促進經濟發展及縮短城鄉距離等關鍵角色。近年來在全球多起地震事件中，有多起山岳隧道受震損害的案例，如:1999年的集集大地震，有49條隧道受到程度不一的損壞；2004年的新潟中越地震，有24條鐵路及山岳隧道受損。有鑒於此對於山岳隧道的耐震安全性逐漸受到重視，過往認為山岳隧道因受周圍岩體包覆，所受慣性力較地上結構物小，不太受到地震影響的觀點被重新檢視。 本研究旨在探討震源距離對山岳隧道受震反應之影響，透過分析案例隧道及鄰近地震測站之監測資料，探討隧道在不同地震震源距離下之動態響應與損害機制，將結果用於建立山岳隧道三維數值模擬方法。最後以數值模擬之結果對案例隧道之受震反應進行分析，並提出建議。 本研究首先回顧國內外山岳隧道受震損害的相關案例與影響因素，以及前人如何透過不同方法探討山岳隧道的受震反應。現地監測記錄分析的部分，取得臺灣東部嘉寶隧道及其鄰近地震站在2014至2016年間記錄之多筆地震資料。透過結合隧道內光纖應變計與加速度歷時分析結果。釐清不同距離震源地震的頻率組成以及隧道受不同距離震源的反應，結果顯示距離隧道較近之地震，地震波傳遞至隧道時，其高頻成分尚未隨距離完全消散，意即高頻成分能量佔比較大，對應波長較短的地動效應是導致隧道受震損壞的原因之一。 數值模擬部分，本研究透過有限元素軟體ABAQUS首先進行二維半無限域地震場動態分析，探討網格尺寸對模擬結果的影響。 後建立現地地形三維模型，並以現地監測資料對模擬結果進行驗證。最後以三維模擬結果，探討隧道不同位置的受震反應。結果顯示在隧道淺覆蓋段，會有特定頻率的振幅被放大，導致同一監測點在不同斷面上，主頻會產生交換。而在與隧道斷面同方向之震波，會因為地震波在洞口段，原先在傳遞之地震波與散射後之地震波疊加導致能量累積，因此在隧道洞口段之能量與加速度峰值會相較隧道一般段來的高。因此在工程設計上，可能須針對隧道洞口段、淺覆蓋度的受震反應進行檢核設計。另外，近源地震的影響亦需詳細分析考慮。

Tunnels, as a vital part of infrastructure, play a crucial role in connecting transportation networks, facilitating economic growth, and reducing distances between urban and rural areas. In recent years, multiple seismic events worldwide have resulted in damage to mountain tunnels. For example, in the 1999 Chi-Chi earthquake, 49 tunnels suffered varying degrees of damage, while the 2004 Niigata Chuetsu earthquake damaged 24 railway and mountain tunnels. Consequently, there is increasing emphasis on the seismic safety of mountain tunnels. The previous assumption—that mountain tunnels, protected by surrounding rock mass, experience smaller inertial forces than above-ground structures and are therefore less susceptible to earthquakes—has been re-evaluated. This study investigates the influence of source distance on the seismic response of mountain tunnels. By analyzing monitoring data from selected case-study tunnels and nearby seismic stations, the study explores the dynamic responses and damage mechanisms under varying earthquake source distances. These findings are then utilized to develop a three-dimensional numerical simulation method for mountain tunnels. Finally, numerical simulation results are analyzed to evaluate seismic responses in the case-study tunnel and provide recommendations. Initially, this research reviews domestic and international cases of seismic damage in mountain tunnels, discussing relevant influencing factors and methodologies previously used to assess tunnel seismic responses. Field monitoring analysis involves examining seismic data collected between 2014 and 2016 from the Jiabao Tunnel in eastern Taiwan and its nearby seismic stations. By integrating data from fiber-optic strain gauges within the tunnel and analyzing acceleration time histories, the study clarifies frequency compositions and tunnel responses under earthquakes originating at various distances. Results indicate that near-field seismic waves, which retain higher frequency components due to limited energy dissipation with distance, contribute significantly to tunnel damage. For the numerical simulations, this study first conducted two-dimensional half‐space dynamic seismic field analyses in ABAQUS to investigate the influence of mesh size on the results. A three‐dimensional model representing the actual terrain was then developed and validated against field monitoring data. Finally, the three‐dimensional simulation results were used to examine the seismic response at different tunnel locations. The results show that in shallow‐cover sections, amplitudes at certain frequencies are amplified, causing the dominant frequency to shift between cross sections at the same monitoring point. Moreover, seismic waves traveling parallel to the tunnel cross section exhibit energy accumulation at the portal due to superposition of incident and scattered waves, resulting in higher energy and peak accelerations at the portal than in mid‐tunnel sections. Therefore, design checks should specifically address portal and shallow‐cover responses, and the effects of near‐source earthquakes must be explicitly considered.