| dc.description.abstract | 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.
| en_US |