地下雙孔隧道受震反應分析

Abstract

隨著都市人口增加，交通堵塞問題日趨嚴重，捷運有著快速、便捷、班次密集與高載客量之特性，儼然成為各大都市高度依賴的交通工具之一。而都市土地價值高，將捷運建造於地下，不但能節省地面空間，亦能減少噪音與干擾。臺灣位於地震活動頻繁之環太平洋地震帶上，當地震發生時，有可能使行駛中之車輛出軌，抑或造成隧道破壞或坍塌。捷運系統所承載人數眾多，若發生意外，可能會造成嚴重的人員傷亡。有鑑於此，本文目的即希望藉由數值模擬分析方法，針對地下隧道受地震力作用之反應做深入之探討。 本研究根據Yang et al. (1996)提出之二維有限元素與無限元素混和模式分析法，模擬土壤-結構互制系統，並結合Zhao和Valliappan (1993)提出之地震力輸入方式，處理波散射問題，進而分析地下隧道結構受到地震力作用下，隧道與土壤間的互制行為，並與前人之研究做比較。另外，也利用實測的921集集地震資料，對單孔或不同排列方式之雙孔隧道，進行地震反應分析。接著，進一步探討土壤、隧道之幾何與材料參數，如：隧道所在深度或隧道間距等，對隧道反應產生之影響。 本研究結果顯示土壤剪力波速與隧道埋置深度，對隧道受震反應影響顯著。而隧道所在深度與排列方式，對於受震後地表反應之影響較不明顯。此外，雙孔水平隧道間交互作用，會使得隧道相鄰側主應力分布狀態改變。

With the increase of urban population, the traffic congestion problem has become more and more serious in metropolitan areas. For its instant, convenient, high frequency service and high capacity characteristics, mass rapid transit (MRT) system has become one of the major transportation tools in metropolitan areas. Owing to the limited and precious ground areas available, most MRT routes have been built as underground tunnels, which can not only save the ground space, but reduce the noise interference. Taiwan is an island located on the circum-Pacific seismic belt where a large number of earthquakes occur each year. When a major earthquake takes place, it may cause the moving MRT trains to derail, or make underground tunnels collapse, thereby resulting in tremendous casualties because of the high capacity characteristics of the system. In view of the above, the purpose of the thesis is to investigate the impact of earthquakes on the underground tunnels by using numerical simulation methods. The study simulated the soil-structure interaction system by using the 2D coupled finite/infinite element approach method proposed by Yang et al. (1996). In order to deal with the wave scattering problem and to analyze the soil-tunnel interaction behaviors subjected to earthquakes, the study also adopted Zhao and Valliappan’s (1993) technique for simulation of the earthquake, and compared the numerical results obtained with the previous studies. Besides, this study investigates the seismic responses of single tunnel and twin-tunnels by utilizing the seismic data recorded during the 921 Chi-Chi Earthquake. Furthermore, parametric studies were conducted to examine the effects of various geometric and material parameters, such as the depth of the tunnels or the space between twin-tunnels, on the tunnel response. The study results show that the soil shear wave velocity and the depth of the tunnels are important parameters with respect to the seismic responses of the tunnels; however, the depth of the tunnels and the relative position of twin-tunnels have less influence on the seismic responses of the ground. In addition, the interaction between the twin-tunnels can result in the change of the principal stresses distribution on the adjacent sides of the two tunnels.