位於軟弱土層中的隧道，由於盾尾間隙閉合引起應力釋放，會導致隧道周圍土壤主應力方向的旋轉並進而產生地拱效應，使得隧道周圍土壓力分佈改變。隧道開挖後之地拱演化關係到隧道襯砌設計及鄰近結構物之安全，因此，必須探討隧道開挖時隧道引致之地拱演化。 本研究利用離心模型試驗，於不同的隧道埋置深度下，探討於砂土層中進行隧道鑽掘導致之土壓力分佈的改變。以體積控制方式模擬土壤漏失量，分別探討（1）隧道崩垮過程中，不同土壤漏失量之隧道崩垮型態與破壞區發展過程。（2）隧道崩垮所導致之地拱演化對於隧道周圍土壓力之影響，主要在釐清於不同的隧道埋置深度下，不同隧道土壤漏失量隧道周圍之土壓力分佈型態。並且針對隧道崩垮後上方影響區域進行研究分析，探討與隧道穩定性的關係。 研究結果顯示，隧道的破壞是由隧道頂拱附近逐漸往地表擴展，頂拱上方破壞半寬度由隧道中心軸起算約為0.8D (D為隧道直徑)。地拱效應會造成有效垂直土壓力隨深度呈非線性分佈，隧道深徑比C/D=3與C/D=4分別以距隧道中心水平距離1.17D~2D與1D~2.5D處之垂直土壓力受拱效應影響最大。並且塑性區發展趨勢為自隧道頂拱往地表擴展，但是未明顯往隧道兩側擴張。針對不同之隧道埋置深度，研究有關隧道上方破壞區域分析可發現，因隧道崩垮而造成隧道上方之破壞區寬度，並未隨隧道的埋置深度改變而改變，而拱效應之影響範圍有隨隧道埋置深度越深而越廣之趨勢。 The stress relaxation due to the closure of tail voids on tunnels in soft soils may cause ground deformation. In turn, soil deformation induced by tunneling will cause principal stress rotation and redistribution of earth pressure. The evolution of arching effect around tunnel is essential for the design of tunnel lining and the safety of nearby structure. The distribution of earth pressure around tunnel need to be studied in detail. A series of centrifuge model tests were performed to assess tunneling-induced ground deformation and the redistribution of earth pressure, when the tunnel was buried at various depths in sandy ground. Two topics were investigated by modeling the ground loss with a volume control technique in this study. First, the evolution of tunnel collapse was analyzed in the case of various ground losses. Second, the influence of the earth pressure on the evolution of arching effect was investigated to evaluate the earth pressure distributions in various ground losses. Furthermore, the deforming zone induced by tunneling was analyzed to understand the stability of tunnel. According to the test results, the following conclusions can be drawn. (1) The settlement zone not only occurred at the crown of the tunnel but gradually developed upward to the ground surface. The settlement area on the surface was symmetric to the tunnel central line and the half-width of settlement area was about 0.8D (D=diameter of tunnel). (2) The plastic zone also occurred at the crown of the tunnel. But it extended vertically to the ground surface until the collapse of tunnel. (3) The different depth of tunnel wouldn’t affect the width of settlement area caused by the collapse of tunnel. But the region of arching effect would extend more wider for a deeper tunnel.
