大台北地區曾發生深開挖造成鄰近捷運隧道損壞之案例，而過去在這方面的數值模擬研究也僅限於二維的靜力分開挖分析，因此，本研究採用三維有限元素法除分析深開挖造成鄰近捷運隧道的變位外，並探討在深開挖過程中如果發生地震時深開挖對於鄰近捷運隧道所產生的影響。一般捷運隧道可分為明挖覆蓋隧道及潛盾隧道，因此本研究亦分別對這兩種隧道做討論。結果顯示(1)無論是靜力或動力分析，深開挖對於隧道的傾斜及下沉影響是比較小的，尤其對埋置深度較深的潛盾隧道，其影響更小。(2)明挖覆蓋隧道，因為位置較淺，在較大地震力作用時，所產生的瞬間水平位移大於埋置深度較深的潛盾隧道所產生者。(3)明挖覆蓋隧道受地震力作用後，所產生額外的位移增量，隨地震力的增加而增加。而潛盾隧道則必需受較大的地震力作用才會產生較明顯的位移增量。(4)隧道於靜力分析時，隧道位移不應太接近規範容許值，否則受地震力作用，將很容易超出規範要求。 In Taipei area there has been reports that the deep excavation performed near the tunnel of Mass Rapid Transit (MRT) System caused the damages to that tunnel. Only two-dimensional static numerical procedure was conducted to investigate such a situation in the past. In this study a three-dimensional finite element procedure is adopted to analyze the displacement of MRT tunnel due to near-by deep excavation and then for each excavation stage the effect of deep excavation on the seismic response of tunnel is investigated. Tunnels studied are open-cut type and shield tunnel. From the parametric studies, it is found that (1) the effect of deep excavation on the settlement and rotation of tunnel is small in static and seismic analyses, especially for the shield tunnel which is in a deeper location;(2) Open-cut tunnel, due to its shallow embedment depth, undergoes larger seismic response than the shield tunnel; (3) The seismic response of open-cut tunnel increases as the depth of excavation increases, while the shield tunnel will have significant increase in displacement only when the earthquake is larger; (4)To avoid the displacement exceeding the safety requirement, it is suggested that the displacement induced by the deep excavation by static analysis should not be very close to the specified value.
