潛盾隧道開挖後由於環片襯砌未能及時架設，形成潛盾機殼與襯砌間之盾尾間隙，在盾尾間隙閉合時使得隧道周圍土壓力產生變化、地盤發生變位。而隧道周圍土壓力的變化會影響襯砌上彎矩等應力的改變，盾尾間隙閉合後產生之地盤變位將影響到鄰近地表結構物產生沈陷以及相關管線之彎曲變形甚至會使鄰近隧道之樁基礎產生變形，因此分析盾尾間隙閉合後隧道環片襯砌應力與周圍地盤變位為一重要課題。 本研究利用有限差分程式FLAC 3.30版，以初始應力平衡之後，立即挖除土壤元素並於隧道底部放入模擬襯砌之樑元素的方式模擬盾尾間隙閉合，探討軟土隧道開挖後，隧道周圍應力傳遞、隧道周圍土壓力分布情形、地表變位、隧道周圍土層垂直與水平變位和襯砌應力等問題，此模擬方式之優點有三，除了可直接獲得盾尾間隙閉合引致之土壤漏失量對襯砌應力的影響，以及襯砌與周圍土層的互制關係、土層自然調節變形後應力重新分佈之變化和土層是否拱化等因素外，尚可直接得到盾尾間隙閉合後之地盤變位。另外本研究尚討論以數值程式模擬離心隧道模型試驗之結果。 潛盾隧道施工引致之盾尾間隙量會使土層產生變形，導致隧道襯砌彎矩及隧道周圍土壓力劇烈變化。當盾尾間隙量持續增加，使土壓力分布不均勻，將造成隧道襯砌彎矩大量增加。此外，依據未襯砌離心隧道模型發展出來之數值程式，應用於模擬單隧道離心模型分析，試驗與數值模擬結果均顯示隧道深徑比愈大，超載係數也會增大，但最大地表沈陷量會減小。上述研究成果可供爾後於考慮盾尾間隙閉合量之襯砌設計及隧道鄰近建物保護範圍參考。 The tail voids between liners and excavated face inevitably developed because liners were unable to be set up on time and to prevent the inward soil movements after excavation of a shield tunnel embedded in soft ground. Tail voids closure causes the stress relief of ground and the change of earth pressure around a tunnel. The different earth pressures applied on the liner induce the different bending moment and the forces. Ground deformation caused by the closure of tail voids may damage structures and lifeline systems adjacent to a tunnel. The stress analysis of the liner and evaluation of ground deformation are one of the key issues for a tunnel designer or a constructor. A finite difference program—FLAC, Version3.3 is used to perform the numerical analysis in the paper. A numerical procedure is used to simulate the effects on the liner for the different amount of the tail void closure. First of all, setting gravity on the domain initializes the in-situ stress and then removing the soil element from the domain simulates the excavation process of the tunnel. At the same time, a series of beam element to form a liner seats directly on the bottom of the tunnel. Finally, the distribution of the earth pressure, the forces in the liner, the settlement trough, vertical and horizontal displacements within the domain are calculated. In addition, the numerical simulations of centrifuge model tests are also simulated. The tail voids due to shield tunneling resulted in soil bodies to deform, and the earth pressure around the tunnel would change its distribution and its value sharply, so that caused the change of bending moments in the tunnel liner. The larger the tail voids, the more non-uniform distribution of earth pressure and the larger bending moments in the tunnel liner were induced. Besides, the overload factor increases with C/D, however, the maximum surface settlement decreases with that. The results can provide the appropriate reference materials design of the liner and the protection of countermeasure structures and foundations adjacent to the tunnel.
