摘 要 位於軟弱土層中的隧道，由於盾尾間隙閉合引起應力釋放，會導致主應力方向旋轉產生地拱效應，使得隧道周圍土壓力分布改變。隧道周圍土壓力分布關係到隧道襯砌設計以及鄰近結構物之安全。因此，必須探討隧道開挖時隧道周圍之土壓力分布。 本研究利用離心模型試驗，探討砂土層中進行隧道鑽掘導致之土壓力分布的改變。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）探討隧道崩垮所導致之地拱效應，對於隧道周圍土壓力之影響，主要在釐清不同隧道土壤漏失量隧道周圍之土壓力分布型態。並且針對隧道側壁上方之水平土壓力進行研究，探討與隧道穩定性的關係。 研究結果顯示，隧道深徑比C/D=3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0.67D（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布，以距隧道中心水平距離1.17D?2D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，而拱效應主要影響區為隧道兩側距隧道中心2.5D範圍內。當隧道破壞之後，塑性區與拱效應主要影響區即不再向外擴展。而隧道側壁上方之有效水平土壓力，由於受到拱效應造成之影響，使得深度小於2.5D處皆增加；而深度大於2.5D則因為土壤進入塑性而降低。因此，造成隧道周圍土壤之側向土壓力係數隨深度而遞減，並非為一常數，因而於評估隧道穩定性時必須加以考慮地拱效應之影響。 The stress relaxation due to the closure of tail voids on tunnels in soft soils may cause the ground deformations. The soil deformations induced by tunneling will cause the stress rotations and changes on the distribution of earth pressure. The distribution of earth pressure around tunnel is essential for the design of tunnel lining and the safety of nearby structure. The variation of earth pressure around tunnel when tunneling are considerably complex and need to be studied in detail. A series of centrifuge model tests were performed to assess tunneling-induced ground deformations in sandy ground and the variations of the distribution of earth pressure. Two topics were investigated by modeling the ground loss with the way of volume control in this study. First of all, the evolution of collapse of tunnel was analyzed in the cases of various ground losses. Secondly, the influence of the earth pressure on the arching effect was investigated to realize the earth pressure distributions in various ground losses. Furthermore, the horizontal earth pressures above the side walls of tunnel were analyzed to comprehend the stability of tunnel. According to the result in the research, for the tunnel with the cover-to-diameter ratio of 3, the soil settlement zone grows from the tunnel axis level toward the ground surface and the half-width of settlement zone is about 0.67D (D=diameter of tunnel) away from tunnel central line. The extent of major arching zone is 2.5D from the tunnel central line. Moreover, the plastic zone grows from the tunnel axis level toward the ground surface and the plastic zone and major arching zone do not extend further even after the tunnel collapse. The arching effect causes the effective horizontal earth pressure above the tunnel side walls to decrease on the condition that the depth z is larger than 2.5D and to increase for z being smaller than 2.5D.
