隨著都市化的急速發展，於擁擠的都市地下空間中進行軟弱土層隧道開挖施工案例日益增多。現行一般多採用潛盾工法來進行隧道開挖工作，在施工過程中，由於地盤應力變化導致周邊地盤變位，亦造成地表結構物受損。此外，施工中的隧道亦可能與營運中的隧道擦身而過，因此如何加強既存隧道的保護以及新挖隧道施工過程的管理與規劃成為相當重要的課題。
針對潛盾施工問題，本研究分為兩大主題來討論：第一部份探討不同深徑比下單隧道盾尾間隙閉合後，地盤應力釋放所造成的隧道襯砌彎矩大小與分佈情況；第二部分則改變不同間徑比，在既存隧道旁開挖新隧道，探討新挖隧道潛盾機的掘進推力、盾尾間隙閉合以及背填灌漿等施工過程中，對既存隧道襯砌彎矩的影響程度。
試驗結果顯示，當隧道深徑比與間徑比都較小的情況下，潛盾推進力會對位於推進面前方的既存隧道襯砌斷面造成較大的彎矩。此外，新挖隧道盾尾間隙閉合，是影響既存隧道襯砌彎矩變化最主要的原因，因此應儘量減少新挖隧道盾尾間隙量同時儘早進行背填灌漿工作，以降低對鄰近既存隧道之影響。

In order to reduce the environmental impacts in crowded cities, new shield tunneling nearby an existing tunnel is very common recently. The change of ground stress due to tunneling processes would cause the displacement of soil around the tunnel, and that would also damage the surface structures and the nearby existing underground structures. There are key issues to strengthen the safety of the existing tunnel and to manage the processes of the new tunneling.
There are two phases in this study. Firstly, a series of single tunnel models with different cover-to-diameter ratios (C/D) in an acceleration of tests 100 g were performed to investigate the bending moments on the tunnel lining during the tail voids closure. Secondly, a new tunnel was drilled nearby the existing tunnel with various distance-to-diameter ratios (d/D), and the jacking force was applied on the tunnel face. The models were conducted to figure out the changes of bending moment on the existing tunnel lining caused by the jacking force, tail voids closure and the back grouting pressure on the new tunnel.
The test results show that the tunnel with smaller values of C/D and of d/D will suffer the larger bending moment on the existing tunnel lining caused by jacking force. A large amount of bending moment on the existing tunnel lining was induced by the tail void closure during tunneling nearby. Thus decreasing the ground loss as small as possible and performing back grouting as early as possible are of essence to prevent the existing tunnel lining from damages.

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