| 摘要: | 本研究利用離心模型試驗，探討於飽和砂土層中進行隧道開挖引致之地盤沉陷與破壞機制及對既存基樁之影響。共進行四部分之研究，分別為單隧道開挖試驗、單隧道開挖周圍土壓力試驗、單隧道開挖對鄰旁既存單樁、群樁之影響試驗。分別探討(1)單隧道開挖引致之地盤沉陷、破壞機制與隧道穩定性；(2)不同隧道土壤漏失量下，隧道周圍地盤之土壓力變化；(3)不同的固定土壤漏失量下，於鄰近隧道旁之單樁進行樁載重試驗，探討因隧道開挖產生土壤漏失量時，單樁之荷重傳遞行為；(4)改變單樁距隧道中心之水平距離與不同樁頭工作荷載，由於隧道開挖引致周圍地盤移動，對鄰近單樁力學行為之影響；(5)改變不同樁長之群樁基礎，進行群樁載重試驗；(6)改變短群樁距隧道中心之水平距離與不同大小工作荷載，探討隧道開挖引致周圍地盤移動，對緊鄰短群樁力學行為之影響；(7)改變不同隧道深徑比與不同長群樁距隧道中心之水平距離，探討因隧道開挖引致周圍地盤移動，對鄰近既存長群樁基礎之影響。
根據研究結果，可於離心模型試驗得知飽和砂土層中隧道開挖周圍地盤變位之情況，地表沉陷量與載重因子有關，當載重因子達0.7時，地表沉陷量會急遽增加。可利用本研究推得之沉陷槽寬度參數與隧道深度之關係式，預測飽和砂土層中之地表沉陷槽寬度值大小，及可利用本研究推得之最大地表沉陷量與隧道直徑比，隨隧道深徑比與土壤漏失量之關係式，在不同隧道深徑比及不同土壤漏失量下，預估地表最大沉陷量。本研究提出了新的隧道破壞機制並與試驗結果驗證，提出隧道有效支撐壓力之評估方法，可有效的評估隧道開挖時維持隧道穩定之臨界支撐壓力與隧道頂拱上方之垂直土壓力。土壤漏失量為VL=1%與2%時，隧道周圍的有效垂直土壓力受到隧道開挖之影響，影響範圍為距隧道中心約1D之處。本研究利用離心模型試驗模擬當隧道產生土壤漏失量時對鄰近基樁進行載重試驗，試驗過程中均可使其達破壞階段，可清楚釐清基樁與隧道之互制關係，進而得到其破壞機制。通隧對鄰近既存樁基礎之影響，主要影響因素為基樁之工作載重比、基樁距離隧道中心的遠近、隧道深徑比及土壤漏失量大小。
;In this study, a series of centrifuge model tests were performed to assess tunneling-induced ground deformations, tunnel stability and their effects on adjacent pile foundations in saturated sandy ground. Four topics have been investigated in this study, the tests of single tunneling, the redistribution of earth pressure induced by single tunneling, and the pile responses caused by single tunneling, respectively. The following topics are discussed: (1) the free-field ground deformations and tunnel stability induced by single tunneling. (2) the distribution of earth pressure around the tunnel induced by single tunneling. (3) the pile loading tests has been analyzed in the different conditions, including the ground loss and the distance between the pile and the tunnel center. (4) the load transfer mechanism of the piles has been analyzed in the different conditions, including ground losses, the load on the pile head, and the distance between the pile and the tunnel center. (5) the pile loading tests has been analyzed in the different piles length. (6) the load transfer mechanism of the short grouped piles has been analyzed in the different conditions, including ground losses, the load on the pile head, and the distance between the pile and the tunnel center. (7) the load transfer mechanism of the long grouped piles has been analyzed in the different conditions, including ground losses, the load on the pile head, and the distance between the pile and the tunnel center.
According to the test results, the ground movement behavior around tunnels embedded in sandy soils below the ground water table was investigated in a series of model tunnel tests in a centrifuge. The degree of ground movement was closely related to the load factor and increased dramatically when the load factor exceeded 0.7. The relation between i and the ratio C/D was derived by regression of the centrifuge model test data; this relation can be used to estimate the width of the surface settlement trough for a tunnel of a particular depth. The maximum surface settlement can be evaluated using the proposed relations of Smax/D and C/D ratio at various ground loss. Importantly, the proposed relations are simple and easy to use in engineering practice. A new failure mechanism was also proposed and validated by comparison with the test results. The proposed failure mechanism enables accurate prediction of two of the key quantities in the design of linings for tunnels embedded in sandy soils, namely the minimum supporting pressure needed to retain tunnel stability and the vertical soil pressure acting on the tunnel crown. When the ground loss reached 1% or 2%, the effect vertical earth pressure around the tunnel due to tunneling, the range of influence from tunnel center about 1D. A series of centrifuge model tests were performed to assess tunneling-induced ground losses and their effects on adjacent pile loading test. The testing process would simulate to failure situation, could clearly clarify the interaction relation between the piles and the tunnel, and then get the load transfer mechanism. The responses of piles caused by nearby tunneling depend mainly on the following factors such as the working load on the pile head, the horizontal distance between the pile and the center of tunnel, the cover-to-diameter of tunnel, and ground loss caused by tunneling. |
