潛盾工法常被採用在軟弱土壤中之隧道工程。由於在開挖的過 程中，鄰近地表面之隧道開挖面穩定分析是一個複雜的三向度問題。 因此，本研究以離心模型試驗探討單隧道開挖面崩潰後，所引致之 地盤沉陷分布型態、孔隙水壓變化及隧道破壞時周圍土體變位情形。 本研究採用大型壓密儀製作等強度剖面之離心模型試體。土體 經由100g 離心加速度下進行再壓密後，在1g 的情況下進行隧道開 挖，並置入6cm 直徑之模型襯砌，模擬現地6m 直徑之隧道。由於 要模擬三向度的問題，所以隧道並沒有貫穿整個土體。在不同試驗 中改變隧道開挖方向前之未襯砌長度(P)。在預定之100g 下逐步調 降支撐氣壓造成隧道變形直至開挖面崩壞。藉由不同之深徑比(C/D) 及未襯砌長度與隧道直徑比(P/D)之隧道模型試驗，對單隧道開挖面 之穩定性做探討。 研究結果顯示，在相同覆土深度時，隨著未襯砌長度之增大， 單隧道崩潰時之超載係數降低、最大地表沉陷量( max d )增大。當 P/D 5 . 0 £ 時，深徑比(C/D)越大時max d 越大；但當P/D 5 . 1 ³ 時，深徑比(C/D) 越大時max d 反而越小。另外，在相同之深徑比(C/D)之下，平面應變 試驗(P/D=¥)之max d 遠大於三維試驗(P/D=0，0.5 及1.5)之max d 。在 相同未襯砌長度時，深徑比越大時其地表沉陷槽寬度也越大。另外， 在相同深徑比下，隧道開挖面之水平位移，隨著P/D 之增大而增大。 潛盾隧道開挖面穩定分析 若己知現場土壤之剪力強度(Su)，便可推估出隧道開挖面崩潰時所 需提供的支撐氣壓。 Shield tunneling is being carried out ever more frequently for tunnel construction in soft ground. During excavation, the face stability analysis of a shallow tunnel is a complex three-dimensional problem. Therefore, a series of single tunnel centrifuge models embedded in soft soils was used to investigate the distributions of surface settlement troughs, the changes of pore water pressure and the collapse mechanisms around the tunnel. The clay beds were consolidated in a rectangular consolidometer. Then the clay bed was reconsolidated in a centrifugal acceleration of 100g. A horizontal hole with 6cm in diameter was carefully cut and a model liner with 6cm in diameter was carefully put inside the hole in 1g to model a liner. The model tested in a centrifuge gravity field of 100g can model a prototype tunnel with 6m in diameter. The tunnel was not penetrated through the whole clay bed in order to simulate a threedimensional problem. After centrifuge acceleration was increased to 100g, the tunnel collapse tests were performed by gradually reducing the air pressure. Model tests with different cover-to-diameter ratio (C/D) and unlined length-to-diameter ratio (P/D) were conducted to investigate the face stability during tunneling in soft ground. For the tunnel having the same cover, the test results show that collapse (OF)c decreases and maximum surface settlement ( max d ) increases with increasing of the unlined length. If the P/D ratio is less than or equal to 0.5, the measured max d increases as the C/D ratio 潛盾隧道開挖面穩定分析 -IVincreases. On the other hand, if the P/D ratio is large than or equal to 1.5, the measured max d decreases as the C/D ratio increases. The values of max d obtained from plane strain tests (P/D=¥) are larger than those obtained from 3D tests (P/D=0,0.5,1.5). For the same P/D ratio, the width of settlement trough increases as the C/D ratio increases. For the same C/D ratio, the horizontal displacement of the tunnel face becomes larger when the P/D ratio is greater. If the shear strength (Su) of soil in the field is known, designers can estimate the possible supporting pressure at collapse.
