本研究呈現一系列的離心模型試驗模擬隧道在液化砂土中的行為與簡易的隧道上浮位移評估方法。在過往的致災性地震中，常發現人孔、地下維生管線等因土壤液化，而造成上浮破壞的現象。對隧道而言，也存在地震引致砂層液化而造成隧道上浮的可能性。本研究使用地工離心機及振動台等試驗設備，在80 g的離心力場下，進行一系列離心模型振動台試驗，來模擬土壤液化引致的隧道上浮反應，觀察破壞模式，並進而提出評估隧道上浮量的方法。 模型試驗的結果發現，隧道於液化土層中的上浮量與其輸入振動的振幅大小、發生液化土層深度的增加而增加；並隨著土層的相對密度以及隧道埋置深度之增加而降低。隧道發生上浮破壞時，在隧道兩側壁土層中發現傾斜的滑動破壞面，而非日本道路橋設計規範所建議的垂直滑動破壞面。作用在隧道底部的超額孔隙水壓力，會隨著振動振幅的增大與基振力作用延時的增長而逐漸的增加。靜水壓與超額孔隙水壓是推動隧道上浮的主要作用力。但在隧道上浮的同時，隧道會因快速上浮的緣故與下方土層分離，此間隙會造成隧道周邊的超額孔隙水壓的下降或增量趨緩。因此在振動期間，隧道周圍的超額孔隙水壓增減與隧道上浮量，具有互為耦合的關係。受到土壤液化的影響，隧道與土壤間的互制效應不明顯，因此並不會加劇隧道上浮的程度。以地中連續壁阻隔外側土壤擠入隧道下方，可以將隧道上浮量減半。 根據離心振動台試驗結果與Sasaki 等人(2004)的試驗結果，本論文提出因土壤液化引致隧道上浮量的簡易評估方法。此方法可有效評估隧道上浮曲線的斜率、隧道上浮的起始時間與終止時間。因此透過本方法可以評估地震時，矩形隧道在液化土層中的上浮量，提供工程師評估隧道上浮量或設計防阻隧道上浮的工程對策的參考。 This dissertation presents the centrifuge modeling tests of embedded tunnels in liquefiable soil and the simplified estimation of tunnel uplift displacement. When the seismic wave is propagating through a loose saturated sand deposit, the seismic wave would disturb the loose sand and produce the excess pore pressure. In the worst scenario, the soil liquefaction happens. If a rectangular tunnel is embedded in the liquefying soil, the excess pore pressure acts on its bottom during the earthquake to drive the tunnel moving upward. In this study, a series of centrifuge modeling tests were conducted in an acceleration of 80 g to investigate the failure mechanism of tunnel uplifting. Through the tests, the tunnel uplifting failure associated with the inclined slip surface was discovered. The tunnel uplift displacement increased as the amplitude of input motion and the liquefaction depth increased. The tunnel uplift displacement decreased as the relative density of soil and the buried depth of tunnel increased. The soil-tunnel interaction was insignificant to the tunnel uplifting behavior especially in the case that the liquefaction depth was deeper than the level of tunnel bottom surface. A simplified uplift prediction of tunnel was proposed based on the observations in this study and the test results reported by Sasaki et al. (2004). The simplified uplift prediction of tunnel, SUPT, is able to determine the starting time and the ending time of tunnel uplifting as well as the slope of tunnel uplift displacement curve if the irregular earthquake motion is converted into the equivalent sinusoidal motion in advance. Thus, SUPT can be used to estimate the complete time-history of tunnel uplift displacement. The evaluated tunnel uplift displacement was consistent with the measured results especially for the cases of large shaking events. Use of cut-off walls to prevent the surrounding soil squeezing into the bottom of tunnel can effectively reduce the tunnel uplift displacement by half.
