近年來，潛盾隧道的施工地點通常位於地狹人稠的都市，且施工過程地盤應力改變會造成鄰近地盤變位，所以在既存隧道旁邊新挖隧道時，可能對既存隧道之結構體產生影響。因此，分析新挖隧道對既存隧道所造成之襯砌彎矩、軸力及剪力之變化以及周圍地盤變位是值得探討之課題。 本研究利用有限元素程式ABAQUS進行隧道開挖模擬。在初始應力平衡後，先進行單隧道開挖模擬，探討單隧道在不同土壤漏失量時的地盤變位及對襯砌之影響。再利用單隧道作為既存隧道，繼續進行新挖隧道開挖之模擬。探討不同深徑比、寬徑比及當既存隧道在不同土壤漏失量時加入襯砌後，新挖隧道開挖對既存隧道之襯砌所產生之影響及探討既存隧道的位移。 單隧道之數值模擬分析結果顯示，在相同土壤漏失量時，深徑比愈大，則地表沉陷槽愈寬，且其襯砌彎矩值、軸力值及剪力值均隨著深徑比愈大而愈大。新挖隧道對既存隧道的影響之數值模擬分析結果顯示，當隧道間距愈小時，既存隧道之襯砌彎矩會愈大，且負彎矩最大值會產生在兩隧道最接近的位置。襯砌軸力的最大值均出現在頂拱的位置，但隧道間距的大小對於襯砌的軸力影響不大。新隧道開挖時，地表沉陷槽漸漸往新挖隧道的上方移動，且當兩隧道間距愈小時，最大地表沉陷量愈大。另外利用數值分析結果與離心模行試驗結果進行比較，可得知新挖隧道對既存隧道之襯砌彎矩發生變化的趨勢大致相同。 Shield tunneling used in the construction of MRT system is increasing recently. The changes of ground stress due to tunneling process would cause the soil displacement around a tunnel. New tunneling near an existing tunnel may cause damages on the tunnel liner. The analyses of the moment, axial force and shear force on the tunnel liner for the existing tunnel and of its displacement are necessary during new tunneling close to an existing tunnel. A finite element program-ABAQUS is used to perform the numerical analysis in the study. First of all, the in-situ stresses are initialized, and then the elements representing the excavated soil in the tunnel were nulled to simulate the excavation process of single tunnel. Secondly, the liner was added to support the earth pressures at various ground losses and the moment, axial force and shear force on the tunnel liner were calculated. Finally a new tunnel close to the existing tunnel with various distances (d/D ratios) was excavated. The impact on the liner of the existing tunnel due to new tunneling was investigated in detail. The results of numerical analysis show that the deeper tunneling produces the wider surface settlement trough. The moment, axial force and shear force of the liner on an existing tunnel increased with the increase of C/D ratio. Tunneling with the smaller d/D ratio develops the larger moment on the liner in the existing tunnel and the maximum negative moment takes place on the portion near to the new tunnel. The maximum axial force takes place on the top of the tunnel liner. The surface settlement trough moves to the side of the new driving tunnel. Beside, the result calculated from the numerical model is considerably consistent with that derived from the centrifuge model tests.
